diff --git a/CHANGELOG.md b/CHANGELOG.md
index 55e9aa7..b0dcc65 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,12 @@ expect rough edges until 1.0.
 ## [Unreleased]
 
 ### Changed
+- **The popover follows your Mac's light or dark mode.** It used to be dark all the time. On a
+  light Mac it is now light glass, with a darker green for text so it stays readable. Settings,
+  About and the other windows follow too, with the same glass or solid background. Selected chips now use dark text on the green
+  instead of white, which was hard to read. If you liked it dark, pick Dark in Settings ›
+  Appearance.
+
 - **The popover is shorter: settings below DPI collapse.** Polling rate, Lighting, Power
   Management, Buttons and Profiles are now compact cards of one row each, each showing
   its current value ("1000 Hz", "Static · 80%", the active profile). Click a row to open its
@@ -39,6 +45,12 @@ expect rough edges until 1.0.
  it reads the answers, using a fake mouse instead of hardware.
 
 ### Added
+- **Settings › Appearance.** Choose the theme for the popover and the app's windows: System
+  (the default), Dark, Light or Razer Green, a dark look with a faint green tint. The popover
+  also gets a thin green edge. Turn off "Glass effect"
+  for a solid background instead of the see-through one. It's easier to read over busy windows.
+  Changes apply straight away, even with the popover open.
+
 - **The Cobra HyperSpeed works over Bluetooth.** Battery, DPI, brightness and lighting
  colour all work with the mouse in Bluetooth mode, so you no longer need the dongle or a
  cable. The battery history carries over too, because the mouse reports the same serial on
diff --git a/Sources/MacRazer/AboutView.swift b/Sources/MacRazer/AboutView.swift
index c4628eb..a7d185c 100644
--- a/Sources/MacRazer/AboutView.swift
+++ b/Sources/MacRazer/AboutView.swift
@@ -65,7 +65,7 @@ struct AboutView: View {
                     Text("by").font(.system(size: 12)).foregroundStyle(.secondary)
                     Link("SorcRR", destination: ProjectLinks.developer)
                         .font(.system(size: 12, weight: .medium))
-                        .foregroundStyle(Color.razerGreen)
+                        .foregroundStyle(Color.razerGreenText)
                 }
                 whatsNewRow
             }
@@ -100,7 +100,7 @@ struct AboutView: View {
                 Link("PR #2583", destination: ProjectLinks.cobraHyperSpeedPR)
             }
             .font(.system(size: 11.5, weight: .medium))
-            .foregroundStyle(Color.razerGreen)
+            .foregroundStyle(Color.razerGreenText)
         }
     }
 
@@ -113,7 +113,7 @@ struct AboutView: View {
                         + "but you run it at your own risk.")
             Link("View the source", destination: ProjectLinks.repo)
                 .font(.system(size: 11.5, weight: .medium))
-                .foregroundStyle(Color.razerGreen)
+                .foregroundStyle(Color.razerGreenText)
         }
     }
 
@@ -131,7 +131,7 @@ struct AboutView: View {
                     Image(systemName: "chevron.right").font(.system(size: 8, weight: .semibold))
                 }
                 .font(.system(size: 11.5, weight: .medium))
-                .foregroundStyle(Color.razerGreen)
+                .foregroundStyle(Color.razerGreenText)
                 .contentShape(Rectangle())
             }
             .buttonStyle(.plain)
@@ -177,7 +177,7 @@ struct AboutView: View {
                 Label("Leave a Tip", systemImage: "heart")
             }
             .buttonStyle(.bordered)
-            .tint(.razerGreen)
+            .tint(.razerGreenText)
             Spacer(minLength: 0)
             Button("Done") { onDone() }
                 .keyboardShortcut(.defaultAction)
diff --git a/Sources/MacRazer/AboutWindowController.swift b/Sources/MacRazer/AboutWindowController.swift
index 50cb0e2..33f3d12 100644
--- a/Sources/MacRazer/AboutWindowController.swift
+++ b/Sources/MacRazer/AboutWindowController.swift
@@ -31,8 +31,8 @@ final class AboutWindowController: AppWindowPresenter {
             w.title = "About MacRazer"
             w.styleMask = [.titled, .closable]
             w.isReleasedWhenClosed = false
-            // Match the popover and the other windows: the green accent needs a dark ground.
-            w.appearance = NSAppearance(named: .darkAqua)
+            // Themed like the popover per Settings › Appearance, kept up to date when it changes.
+            AppearanceSettings.shared.track(w)
             w.center()
             hosting = controller
             window = w
diff --git a/Sources/MacRazer/AppDelegate.swift b/Sources/MacRazer/AppDelegate.swift
index 699fea5..064cafc 100644
--- a/Sources/MacRazer/AppDelegate.swift
+++ b/Sources/MacRazer/AppDelegate.swift
@@ -25,6 +25,9 @@ final class AppDelegate: NSObject, NSApplicationDelegate, NSPopoverDelegate, UNU
         model: DeviceTestModel(controller: controller, permissions: permissions))
     private let updateChecker = UpdateChecker()
     private let launchAtLogin = LaunchAtLogin()
+    private let appearance = AppearanceSettings.shared
+    /// The solid colour or green tint behind the popover; see `PopoverBackdropView`.
+    private let popoverBackdrop = PopoverBackdropView()
     private lazy var aboutWindow = AboutWindowController()
     /// Closing it re-asks the auto-install gate. This window opens unfocused after an
     /// automatic install and can sit unnoticed for days, and while it is open it holds back
@@ -103,13 +106,20 @@ final class AppDelegate: NSObject, NSApplicationDelegate, NSPopoverDelegate, UNU
         popover.behavior = .transient
         popover.delegate = self
         popover.animates = false // open immediately, no slide animation
-        // Force a dark popover regardless of system appearance — the Razer-green accent and
-        // logo have poor contrast on the light-mode grey material; dark is also the gaming
-        // aesthetic and makes the green pop.
-        popover.appearance = NSAppearance(named: .darkAqua)
+        // Light or dark, glass or solid, per Settings › Appearance. Re-applied whenever the
+        // setting changes or macOS switches between light and dark, including while the
+        // popover is open. The popover's appearance is always set explicitly, never left nil:
+        // a nil one would follow the menu bar, which macOS tints from the wallpaper rather
+        // than the system's light or dark mode.
+        Publishers.CombineLatest3(appearance.$theme, appearance.$glass,
+                                  NSApp.publisher(for: \.effectiveAppearance))
+            .sink { [weak self] theme, glass, system in
+                self?.applyAppearance(theme: theme, glass: glass, systemIsDark: system.isDark)
+            }
+            .store(in: &cancellables)
         let hosting = NSHostingController(rootView: PopoverView(
             controller: controller, remapper: remapper, updateChecker: updateChecker,
-            launchAtLogin: launchAtLogin,
+            launchAtLogin: launchAtLogin, appearance: appearance,
             onOpenSettings: { [weak self] in
                 // Close first: the popover is transient and would dismiss itself the moment
                 // the window takes focus, which looks like the click did two things.
@@ -367,6 +377,8 @@ final class AppDelegate: NSObject, NSApplicationDelegate, NSPopoverDelegate, UNU
             windowsBeforePopover = Set(NSApp.windows.filter(\.isVisible).map(ObjectIdentifier.init))
             // Show first (instant), then kick off the refresh so the open never waits on IO.
             popover.show(relativeTo: button.bounds, of: button, preferredEdge: .minY)
+            // The frame view the backdrop lives in only exists once the popover is shown.
+            installPopoverBackdrop()
             // Activate, not just make key. This app has no Dock icon, so clicking the menu bar
             // item does not make it the active application, and a control in an inactive app's
             // window does not respond to the first click the way it looks like it should. Every
@@ -510,6 +522,27 @@ final class AppDelegate: NSObject, NSApplicationDelegate, NSPopoverDelegate, UNU
     @objc private func openDeviceTest() { present(deviceTestWindow) }
     @objc private func quit() { NSApplication.shared.terminate(nil) }
 
+    // MARK: - Appearance
+
+    private func applyAppearance(theme: PopoverTheme, glass: Bool, systemIsDark: Bool) {
+        let look = PopoverLook.resolve(theme: theme, glass: glass, systemIsDark: systemIsDark)
+        popover.appearance = NSAppearance(named: look.appearanceName)
+        popoverBackdrop.fill = look.backdropColor
+        appearance.applyToWindows(look)
+    }
+
+    /// Puts the backdrop into the popover's frame view, just under the content: above the
+    /// native material, so a solid colour hides it, and filling the arrow too. NSPopover
+    /// keeps its frame view between shows, so this only does work the first time.
+    private func installPopoverBackdrop() {
+        guard let content = popover.contentViewController?.view,
+              let frameView = content.superview,
+              popoverBackdrop.superview !== frameView else { return }
+        popoverBackdrop.frame = frameView.bounds
+        popoverBackdrop.autoresizingMask = [.width, .height]
+        frameView.addSubview(popoverBackdrop, positioned: .below, relativeTo: content)
+    }
+
     // MARK: - NSPopoverDelegate
 
     func popoverDidShow(_ notification: Notification) { controller.setPopoverVisible(true) }
diff --git a/Sources/MacRazer/ColorPickerPage.swift b/Sources/MacRazer/ColorPickerPage.swift
index e3713f5..f00df44 100644
--- a/Sources/MacRazer/ColorPickerPage.swift
+++ b/Sources/MacRazer/ColorPickerPage.swift
@@ -49,7 +49,7 @@ struct ColorPickerPage: View {
                 Text("Colour").font(.system(size: 16, weight: .semibold))
                 Spacer()
                 Circle().fill(color).frame(width: 22, height: 22)
-                    .overlay(Circle().strokeBorder(.white.opacity(0.35), lineWidth: 1))
+                    .overlay(Circle().strokeBorder(Color.primary.opacity(0.25), lineWidth: 1))
             }
             wheel
             HStack(spacing: 8) {
@@ -76,7 +76,7 @@ struct ColorPickerPage: View {
                         gradient: Gradient(colors: [.white, .white.opacity(0)]),
                         center: .center, startRadius: 0, endRadius: r)))
                     .overlay(Circle().fill(.black.opacity(1 - bri)))
-                    .overlay(Circle().strokeBorder(.white.opacity(0.15), lineWidth: 1))
+                    .overlay(Circle().strokeBorder(Color.primary.opacity(0.15), lineWidth: 1))
                     .frame(width: side, height: side)
                 Circle().stroke(.white, lineWidth: 2)
                     .frame(width: 15, height: 15)
diff --git a/Sources/MacRazer/CrashReportView.swift b/Sources/MacRazer/CrashReportView.swift
index 3ab16b6..65a0d33 100644
--- a/Sources/MacRazer/CrashReportView.swift
+++ b/Sources/MacRazer/CrashReportView.swift
@@ -78,6 +78,10 @@ struct CrashReportView: View {
                                      set: { model.comment = String($0.prefix(DeviceReportOutput.maxComment)) }))
                 .font(.system(size: 12))
                 .frame(height: 54)
+                // The editor's own opaque background would sit as a flat box on a glass or tinted
+                // window; a faint fill like the cards keeps it readable on all of them.
+                .scrollContentBackground(.hidden)
+                .background(Color.primary.opacity(0.05), in: RoundedRectangle(cornerRadius: 6))
                 .overlay(alignment: .topLeading) {
                     if model.comment.isEmpty {
                         Text("What were you doing when it quit? (optional)")
diff --git a/Sources/MacRazer/CrashReportWindowController.swift b/Sources/MacRazer/CrashReportWindowController.swift
index 0e88ed2..e5229e9 100644
--- a/Sources/MacRazer/CrashReportWindowController.swift
+++ b/Sources/MacRazer/CrashReportWindowController.swift
@@ -60,8 +60,8 @@ final class CrashReportWindowController: NSObject, AppWindowPresenter, NSWindowD
             w.title = "MacRazer Crash Report"
             w.styleMask = [.titled, .closable]
             w.isReleasedWhenClosed = false
-            // Match the other windows: the green accent needs a dark ground.
-            w.appearance = NSAppearance(named: .darkAqua)
+            // Themed like the popover per Settings › Appearance, kept up to date when it changes.
+            AppearanceSettings.shared.track(w)
             w.delegate = self
             w.center()
             window = w
diff --git a/Sources/MacRazer/DeviceTestView.swift b/Sources/MacRazer/DeviceTestView.swift
index eab58f0..7ef92e6 100644
--- a/Sources/MacRazer/DeviceTestView.swift
+++ b/Sources/MacRazer/DeviceTestView.swift
@@ -53,7 +53,7 @@ struct DeviceTestView: View {
     private var intro: some View {
         VStack(alignment: .leading, spacing: 12) {
             if model.isKnownSupported {
-                tag("Fully supported", color: .razerGreen)
+                tag("Fully supported", color: .razerGreenText)
                 title("Your \(model.deviceName) is already supported")
                 note("The test checks it really works on your mouse and firmware. Reports like this keep the supported list honest, and catch it early if a firmware update breaks something.")
             } else {
@@ -165,7 +165,7 @@ struct DeviceTestView: View {
                     VStack(spacing: 4) {
                         row("Yours", record.data?.original.map(String.init) ?? "No answer")
                         row("Test, read back", "\(record.data?.test.map(String.init) ?? "–"), \(record.data?.readBack.map(String.init) ?? "–")")
-                        row("Put back", record.data?.restored == true ? "Yes" : "No", color: record.data?.restored == true ? .razerGreen : .batteryMid)
+                        row("Put back", record.data?.restored == true ? "Yes" : "No", color: record.data?.restored == true ? .razerGreenText : .batteryMid)
                         if let stages = record.data?.stages { row("Stages", stages.map(String.init).joined(separator: " · ")) }
                         if let max = record.data?.maxProbe { row("Highest it kept", String(max)) }
                     }
@@ -195,7 +195,7 @@ struct DeviceTestView: View {
                     VStack(spacing: 4) {
                         row("Yours", record.data?.original.map { "\($0) Hz" } ?? "No answer")
                         row("Test, read back", "\(record.data?.test.map { "\($0) Hz" } ?? "–"), \(record.data?.readBack.map { "\($0) Hz" } ?? "–")")
-                        row("Put back", record.data?.restored == true ? "Yes" : "No", color: record.data?.restored == true ? .razerGreen : .batteryMid)
+                        row("Put back", record.data?.restored == true ? "Yes" : "No", color: record.data?.restored == true ? .razerGreenText : .batteryMid)
                     }
                 }
                 outcomeRow("Polling rate", record.outcome)
@@ -257,7 +257,7 @@ struct DeviceTestView: View {
                 card {
                     VStack(spacing: 4) {
                         row(report.device.name, String(format: "0x%04X", report.device.productID) + (report.identify.data?.firmware.map { ", \($0)" } ?? ""))
-                        if !verdict.passed.isEmpty { row("Worked", verdict.passed.joined(separator: ", "), color: .razerGreen) }
+                        if !verdict.passed.isEmpty { row("Worked", verdict.passed.joined(separator: ", "), color: .razerGreenText) }
                         if !verdict.failed.isEmpty { row("Didn't work", verdict.failed.joined(separator: ", "), color: .batteryMid) }
                         if !verdict.notSupported.isEmpty { row("Not on this mouse", verdict.notSupported.joined(separator: ", ")) }
                         if !verdict.skipped.isEmpty { row("Skipped", verdict.skipped.joined(separator: ", ")) }
@@ -284,6 +284,10 @@ struct DeviceTestView: View {
                                          set: { model.comment = String($0.prefix(DeviceReportOutput.maxComment)) }))
                     .font(.system(size: 12))
                     .frame(height: 54)
+                    // The editor's own opaque background would sit as a flat box on a glass or tinted
+                    // window; a faint fill like the cards keeps it readable on all of them.
+                    .scrollContentBackground(.hidden)
+                    .background(Color.primary.opacity(0.05), in: RoundedRectangle(cornerRadius: 6))
                     .overlay(alignment: .topLeading) {
                         if model.comment.isEmpty {
                             Text("Comments or feedback (optional)").font(.system(size: 12)).foregroundStyle(.tertiary)
@@ -366,7 +370,7 @@ struct DeviceTestView: View {
     private func stepTitle(_ text: String, changes: Bool) -> some View {
         HStack(spacing: 8) {
             title(text)
-            tag(changes ? "Changes, then puts back" : "Reads only", color: changes ? .batteryMid : .razerGreen)
+            tag(changes ? "Changes, then puts back" : "Reads only", color: changes ? .batteryMid : .razerGreenText)
         }
     }
 
@@ -403,7 +407,7 @@ struct DeviceTestView: View {
     private func outcomeRow(_ label: String, _ outcome: DeviceReport.Outcome) -> some View {
         let (text, color): (String, Color) = {
             switch outcome {
-            case .passed: return ("Works", .razerGreen)
+            case .passed: return ("Works", .razerGreenText)
             case .failed: return ("Didn't work", .batteryMid)
             case .notSupported: return ("Not on this mouse", .secondary)
             case .skipped: return ("Skipped", .secondary)
diff --git a/Sources/MacRazer/DeviceTestWindowController.swift b/Sources/MacRazer/DeviceTestWindowController.swift
index 9ee923c..13b0a1b 100644
--- a/Sources/MacRazer/DeviceTestWindowController.swift
+++ b/Sources/MacRazer/DeviceTestWindowController.swift
@@ -21,8 +21,8 @@ final class DeviceTestWindowController: NSObject, AppWindowPresenter, NSWindowDe
             let w = NSWindow(contentViewController: hosting)
             w.styleMask = [.titled, .closable]
             w.isReleasedWhenClosed = false
-            // Match the popover's forced-dark look, like the app's other windows.
-            w.appearance = NSAppearance(named: .darkAqua)
+            // Themed like the popover per Settings › Appearance, kept up to date when it changes.
+            AppearanceSettings.shared.track(w)
             w.delegate = self
             w.center()
             window = w
diff --git a/Sources/MacRazer/PermissionsWindowController.swift b/Sources/MacRazer/PermissionsWindowController.swift
index cfd096c..c676b05 100644
--- a/Sources/MacRazer/PermissionsWindowController.swift
+++ b/Sources/MacRazer/PermissionsWindowController.swift
@@ -29,8 +29,8 @@ final class PermissionsWindowController: AppWindowPresenter {
             w.title = "MacRazer Setup"
             w.styleMask = [.titled, .closable]
             w.isReleasedWhenClosed = false
-            // Match the popover's forced-dark look so the green accent reads correctly.
-            w.appearance = NSAppearance(named: .darkAqua)
+            // Themed like the popover per Settings › Appearance, kept up to date when it changes.
+            AppearanceSettings.shared.track(w)
             w.center()
             window = w
         }
diff --git a/Sources/MacRazer/PopoverTheme.swift b/Sources/MacRazer/PopoverTheme.swift
new file mode 100644
index 0000000..c32a5ad
--- /dev/null
+++ b/Sources/MacRazer/PopoverTheme.swift
@@ -0,0 +1,212 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+// Part of MacRazer, a control app for Razer mice on macOS. See LICENSE and NOTICE.md.
+
+import AppKit
+import Combine
+
+/// The theme picked in Settings › Appearance.
+enum PopoverTheme: String, CaseIterable, Identifiable {
+    case system, dark, light, razerGreen
+
+    var id: String { rawValue }
+
+    var title: String {
+        switch self {
+        case .system: return "System"
+        case .dark: return "Dark"
+        case .light: return "Light"
+        case .razerGreen: return "Razer Green"
+        }
+    }
+}
+
+/// What the popover and the app's windows actually look like once the theme, the glass switch
+/// and the system's light or dark mode are combined. One case per mockup.
+enum PopoverLook: Equatable, CaseIterable {
+    case lightGlass, darkGlass, greenGlass
+    case solidLight, solidDark, solidGreen
+
+    /// Every combination in one place, so the popover, its arrow and the tests can't disagree.
+    /// Razer Green is always dark: a light green tint looks washed out.
+    static func resolve(theme: PopoverTheme, glass: Bool, systemIsDark: Bool) -> PopoverLook {
+        switch theme {
+        case .system: return systemIsDark ? (glass ? .darkGlass : .solidDark) : (glass ? .lightGlass : .solidLight)
+        case .dark: return glass ? .darkGlass : .solidDark
+        case .light: return glass ? .lightGlass : .solidLight
+        case .razerGreen: return glass ? .greenGlass : .solidGreen
+        }
+    }
+
+    var isDark: Bool {
+        switch self {
+        case .lightGlass, .solidLight: return false
+        case .darkGlass, .greenGlass, .solidDark, .solidGreen: return true
+        }
+    }
+
+    var isGlass: Bool {
+        switch self {
+        case .lightGlass, .darkGlass, .greenGlass: return true
+        case .solidLight, .solidDark, .solidGreen: return false
+        }
+    }
+
+    /// Whether the thin green edge goes round the popover.
+    var hasGreenEdge: Bool { self == .greenGlass }
+
+    /// What's painted over the popover's own material, arrow included. Nil leaves the native
+    /// glass as it is. Solid looks are opaque; the green glass is a faint tint.
+    var backdropColor: NSColor? {
+        switch self {
+        case .lightGlass, .darkGlass: return nil
+        case .greenGlass: return NSColor(hex: 0x103A14, alpha: 0.35)
+        case .solidLight: return NSColor(hex: 0xF5F5F7)
+        case .solidDark: return NSColor(hex: 0x1C1C1E)
+        case .solidGreen: return NSColor(hex: 0x0F1A11)
+        }
+    }
+
+    var appearanceName: NSAppearance.Name { isDark ? .darkAqua : .aqua }
+}
+
+/// The Appearance settings, stored in UserDefaults. Shared by the Settings window, which
+/// edits them, and the app delegate, which applies them to the popover and the windows.
+@MainActor
+final class AppearanceSettings: ObservableObject {
+    static let themeKey = "appearance.theme"
+    static let glassKey = "appearance.glass"
+
+    /// The app's one instance. The window controllers reach it here rather than having it
+    /// threaded through every initializer; tests make their own with a scratch defaults suite.
+    static let shared = AppearanceSettings()
+
+    private let defaults: UserDefaults
+
+    @Published var theme: PopoverTheme {
+        didSet { defaults.set(theme.rawValue, forKey: Self.themeKey) }
+    }
+    @Published var glass: Bool {
+        didSet { defaults.set(glass, forKey: Self.glassKey) }
+    }
+
+    init(defaults: UserDefaults = .standard) {
+        self.defaults = defaults
+        // An unknown stored value (a theme removed in a later version) falls back to System
+        // rather than failing.
+        theme = defaults.string(forKey: Self.themeKey).flatMap(PopoverTheme.init(rawValue:)) ?? .system
+        glass = defaults.object(forKey: Self.glassKey) as? Bool ?? true
+    }
+
+    func look(systemIsDark: Bool) -> PopoverLook {
+        PopoverLook.resolve(theme: theme, glass: glass, systemIsDark: systemIsDark)
+    }
+
+    // MARK: Windows
+
+    private let windows = NSHashTable<NSWindow>.weakObjects()
+    /// The look last given to the windows, so a window opened later matches them.
+    private var windowLook: PopoverLook?
+
+    /// Gives a window the current look (glass or solid, light, dark or green) and keeps it
+    /// updated when the setting or the system's light or dark mode changes.
+    func track(_ window: NSWindow) {
+        windows.add(window)
+        let look = windowLook ?? look(systemIsDark: NSApplication.shared.effectiveAppearance.isDark)
+        WindowBackdrop.apply(look, to: window)
+    }
+
+    /// Re-applies a look to every tracked window. Takes the look rather than working it out
+    /// from `theme`, because the owner calls this from a `$theme` subscriber, which runs before
+    /// the property itself has changed.
+    func applyToWindows(_ look: PopoverLook) {
+        windowLook = look
+        for window in windows.allObjects { WindowBackdrop.apply(look, to: window) }
+    }
+}
+
+/// Puts a `PopoverLook` on an ordinary window: the same glass, solid colour or green tint as
+/// the popover, so Settings and the other windows match it.
+///
+/// Like the popover's backdrop, the glass and the tint sit in the window's frame view, just
+/// under the content, so they also cover the title bar.
+@MainActor
+enum WindowBackdrop {
+    private static let glassID = NSUserInterfaceItemIdentifier("MacRazer.windowGlass")
+    private static let tintID = NSUserInterfaceItemIdentifier("MacRazer.windowTint")
+
+    static func apply(_ look: PopoverLook, to window: NSWindow) {
+        window.appearance = NSAppearance(named: look.appearanceName)
+        // The title bar shows whatever is behind it, so it matches the rest of the window
+        // instead of drawing its own grey strip.
+        window.titlebarAppearsTransparent = true
+        let (glass, tint) = layers(in: window)
+        if look.isGlass {
+            window.isOpaque = false
+            window.backgroundColor = .clear
+            glass?.isHidden = false
+            tint?.fill = look.backdropColor
+        } else {
+            window.isOpaque = true
+            window.backgroundColor = look.backdropColor
+            glass?.isHidden = true
+            tint?.fill = nil
+        }
+    }
+
+    /// The window's glass and tint views, added the first time.
+    private static func layers(in window: NSWindow) -> (NSVisualEffectView?, PopoverBackdropView?) {
+        guard let content = window.contentView, let frameView = content.superview else { return (nil, nil) }
+        if let glass = frameView.subviews.first(where: { $0.identifier == glassID }) as? NSVisualEffectView,
+           let tint = frameView.subviews.first(where: { $0.identifier == tintID }) as? PopoverBackdropView {
+            return (glass, tint)
+        }
+        let glass = NSVisualEffectView(frame: frameView.bounds)
+        glass.identifier = glassID
+        // The popover's own material, so a window and the popover read as the same glass.
+        glass.material = .popover
+        glass.blendingMode = .behindWindow
+        // Stay glass when the window isn't key, rather than going flat grey.
+        glass.state = .active
+        glass.autoresizingMask = [.width, .height]
+        let tint = PopoverBackdropView(frame: frameView.bounds)
+        tint.identifier = tintID
+        tint.autoresizingMask = [.width, .height]
+        frameView.addSubview(glass, positioned: .below, relativeTo: content)
+        frameView.addSubview(tint, positioned: .below, relativeTo: content)
+        return (glass, tint)
+    }
+}
+
+extension NSColor {
+    /// An sRGB colour from `0xRRGGBB`, the way the mockups and the docs write them.
+    convenience init(hex: UInt32, alpha: CGFloat = 1) {
+        self.init(srgbRed: CGFloat((hex >> 16) & 0xFF) / 255, green: CGFloat((hex >> 8) & 0xFF) / 255,
+                  blue: CGFloat(hex & 0xFF) / 255, alpha: alpha)
+    }
+}
+
+extension NSAppearance {
+    var isDark: Bool { bestMatch(from: [.aqua, .darkAqua]) == .darkAqua }
+}
+
+/// Paints the solid colour (or the green tint) behind the popover's content. `WindowBackdrop`
+/// reuses it as the green tint on the app's windows.
+///
+/// It sits in the popover's frame view rather than in SwiftUI, because the arrow is drawn by
+/// that frame view, outside the content. A SwiftUI background would leave the arrow glass
+/// while the body went solid. The frame view clips its subviews to the popover's outline,
+/// arrow included, so filling the whole bounds fills exactly the popover.
+final class PopoverBackdropView: NSView {
+    var fill: NSColor? {
+        didSet { isHidden = fill == nil; needsDisplay = true }
+    }
+
+    override func draw(_ dirtyRect: NSRect) {
+        guard let fill else { return }
+        fill.setFill()
+        dirtyRect.fill(using: .sourceOver)
+    }
+
+    /// Clicks go to the content, never to the backdrop.
+    override func hitTest(_ point: NSPoint) -> NSView? { nil }
+}
diff --git a/Sources/MacRazer/PopoverView.swift b/Sources/MacRazer/PopoverView.swift
index 32a9b4d..66114a2 100644
--- a/Sources/MacRazer/PopoverView.swift
+++ b/Sources/MacRazer/PopoverView.swift
@@ -10,14 +10,28 @@ private struct HeightKey: PreferenceKey {
     static func reduce(value: inout CGFloat, nextValue: () -> CGFloat) { value = max(value, nextValue()) }
 }
 
+/// A colour with one value for light surfaces and one for dark, picked by whatever the view is
+/// drawn in. The popover and windows can be either, depending on Settings › Appearance.
+private func adaptive(light: NSColor, dark: NSColor) -> Color {
+    Color(nsColor: NSColor(name: nil) { $0.isDark ? dark : light })
+}
+
 extension Color {
-    /// Razer brand green (#44D62C) — the single accent. Budget: logo, slider, active chip/segment.
-    static let razerGreen = Color(red: 0x44 / 255, green: 0xD6 / 255, blue: 0x2C / 255)
-    /// A brighter, more vivid green for the logo so it really pops on the dark background.
-    static let razerGreenBright = Color(red: 0.42, green: 1.0, blue: 0.25)
-    /// The Bluetooth chip's colour. System blue is too dark to read on the popover's dark
-    /// background.
-    static let bluetoothBlue = Color(red: 0.47, green: 0.72, blue: 1.0)
+    /// Razer brand green (#44D62C) — the single accent, as a fill: slider, active chip/segment,
+    /// switches. The same in light and dark. For green text or icons use `razerGreenText`.
+    static let razerGreen = Color(nsColor: NSColor(hex: 0x44D62C))
+    /// Green for text and icons. The brand green is too light to read on a light background,
+    /// so light surfaces get a darker green (#23891A).
+    static let razerGreenText = adaptive(light: NSColor(hex: 0x23891A), dark: NSColor(hex: 0x44D62C))
+    /// Text and icons drawn on a `razerGreen` fill. Dark in every theme: white on #44D62C is
+    /// only about 1.9:1 contrast.
+    static let onRazerGreen = Color(nsColor: NSColor(hex: 0x0D2B07))
+    /// The logo's green: brighter than the brand green so it pops on dark, and the darker
+    /// text green on light, where a bright green washes out.
+    static let razerGreenBright = adaptive(light: NSColor(hex: 0x23891A), dark: NSColor(hex: 0x6BFF40))
+    /// The Bluetooth chip's colour. System blue is too dark to read on a dark background,
+    /// and this lighter blue too pale on a light one.
+    static let bluetoothBlue = adaptive(light: NSColor(hex: 0x0A64D6), dark: NSColor(hex: 0x78B8FF))
     // Battery *state* uses Apple system colors (meaning), never the brand green.
     static let batteryFull = Color(red: 0x34 / 255, green: 0xC7 / 255, blue: 0x59 / 255)
     static let batteryMid = Color(red: 0xFF / 255, green: 0x9F / 255, blue: 0x0A / 255)
@@ -29,6 +43,10 @@ struct PopoverView: View {
     @ObservedObject var remapper: ButtonRemapper
     @ObservedObject var updateChecker: UpdateChecker
     @ObservedObject var launchAtLogin: LaunchAtLogin
+    /// Settings › Appearance; only the Razer Green glass edge is drawn here. The rest is the
+    /// popover's appearance and backdrop, which the app delegate sets.
+    @ObservedObject var appearance: AppearanceSettings
+    @Environment(\.colorScheme) private var colorScheme
     /// Opening a window is the owner's job — the popover doesn't know about window controllers.
     /// Deliberately not defaulted: a no-op default would let a future call site forget the
     /// handler and ship a gear button that depresses and does nothing, with no compiler error.
@@ -88,6 +106,9 @@ struct PopoverView: View {
     /// Not the colour page: it's a fixed-size picker, centred, and would only gain empty space.
     private let subPageMinHeight: CGFloat = 560
     @State private var mainHeight: CGFloat = 0
+    /// The corner radius NSPopover gives its body, so the green edge sits on the outline.
+    /// Measured from a capture on macOS 26; the content view is exactly the body.
+    static let popoverCornerRadius: CGFloat = 10
 
     var body: some View {
         ZStack {
@@ -107,6 +128,15 @@ struct PopoverView: View {
         // main page's height instead of resizing once the transition finishes.
         .onPreferenceChange(HeightKey.self) { if $0 > 0 { mainHeight = $0 } }
         .animation(.easeInOut(duration: 0.26), value: page)
+        .overlay {
+            if appearance.look(systemIsDark: colorScheme == .dark).hasGreenEdge {
+                // Follows the body's rounded outline; the arrow above it has no edge.
+                RoundedRectangle(cornerRadius: Self.popoverCornerRadius)
+                    .strokeBorder(Color.razerGreen.opacity(0.45), lineWidth: 1)
+                    .ignoresSafeArea()
+                    .allowsHitTesting(false)
+            }
+        }
         // Closing the popover resets navigation: reopening onto a stale sub-page (whose
         // gating card may have been disabled in the meantime — e.g. Profiles after a
         // disconnect) is disorienting.
@@ -278,7 +308,7 @@ struct PopoverView: View {
                             .font(.system(size: 11, weight: .medium))
                     }
                     .buttonStyle(.borderless)
-                    .foregroundStyle(Color.razerGreen)
+                    .foregroundStyle(Color.razerGreenText)
                 } else {
                     Button {
                         controller.refreshAll()
@@ -356,7 +386,7 @@ struct PopoverView: View {
                                 Image(systemName: "arrow.right").font(.system(size: 9, weight: .semibold))
                             }
                             .font(.system(size: 11, weight: .medium))
-                            .foregroundStyle(Color.razerGreen)
+                            .foregroundStyle(Color.razerGreenText)
                         }
                         .buttonStyle(.plain)
                     }
@@ -414,7 +444,7 @@ struct PopoverView: View {
     private struct ConnectionChip {
         let symbol: String
         let label: String
-        var tint: Color = .razerGreen
+        var tint: Color = .razerGreenText
         var fillOpacity: Double = 0.15
     }
 
@@ -493,7 +523,7 @@ struct PopoverView: View {
                 Button("Manage Profiles…") { page = .profiles }
                     .buttonStyle(.plain)
                     .font(.system(size: 11, weight: .medium))
-                    .foregroundStyle(Color.razerGreen)
+                    .foregroundStyle(Color.razerGreenText)
             }
         }
     }
@@ -512,7 +542,7 @@ struct PopoverView: View {
         }
         .buttonStyle(.plain)
         .font(.system(size: 10.5, weight: active ? .semibold : .regular))
-        .foregroundStyle(active ? .white : .secondary)
+        .foregroundStyle(active ? Color.onRazerGreen : Color.secondary)
         .frame(height: 24)
         .background(active ? Color.razerGreen : Color.primary.opacity(0.08), in: Capsule())
         .hoverHighlight(Capsule())
@@ -537,7 +567,7 @@ struct PopoverView: View {
             Image(systemName: "plus").font(.system(size: 10.5, weight: .semibold))
         }
         .buttonStyle(.plain)
-        .foregroundStyle(Color.razerGreen)
+        .foregroundStyle(Color.razerGreenText)
         .frame(width: 24, height: 24)
         .background(Color.razerGreen.opacity(0.12), in: Circle())
         .overlay(Circle().stroke(Color.razerGreen.opacity(0.55), lineWidth: 1))
@@ -579,7 +609,7 @@ struct PopoverView: View {
         VStack(alignment: .leading, spacing: 8) {
             HStack(alignment: .top, spacing: 8) {
                 Image(systemName: "arrow.down.circle.fill")
-                    .foregroundStyle(Color.razerGreen)
+                    .foregroundStyle(Color.razerGreenText)
                     .font(.system(size: 14, weight: .semibold))
                 VStack(alignment: .leading, spacing: 1) {
                     Text("Update available").font(.system(size: 12, weight: .semibold))
@@ -616,7 +646,7 @@ struct PopoverView: View {
                         Spacer(minLength: 0)
                         Image(systemName: "chevron.right").font(.system(size: 9, weight: .semibold))
                     }
-                    .foregroundStyle(Color.razerGreen)
+                    .foregroundStyle(Color.razerGreenText)
                     .contentShape(Rectangle())
                 }
                 .buttonStyle(.plain)
@@ -636,7 +666,7 @@ struct PopoverView: View {
                 }
                 .buttonStyle(.plain)
                 .font(.system(size: 11))
-                .foregroundStyle(Color.razerGreen)
+                .foregroundStyle(Color.razerGreenText)
             }
         }
         .padding(12)
@@ -701,7 +731,7 @@ struct PopoverView: View {
         VStack(alignment: .leading, spacing: 8) {
             HStack(alignment: .top, spacing: 8) {
                 Image(systemName: "checkmark.circle.fill")
-                    .foregroundStyle(Color.razerGreen)
+                    .foregroundStyle(Color.razerGreenText)
                     .font(.system(size: 14, weight: .semibold))
                 VStack(alignment: .leading, spacing: 1) {
                     Text("Updated to \(appVersion)").font(.system(size: 12, weight: .semibold))
@@ -728,7 +758,7 @@ struct PopoverView: View {
                         Spacer(minLength: 0)
                         Image(systemName: "chevron.right").font(.system(size: 9, weight: .semibold))
                     }
-                    .foregroundStyle(Color.razerGreen)
+                    .foregroundStyle(Color.razerGreenText)
                     .contentShape(Rectangle())
                 }
                 .buttonStyle(.plain)
@@ -826,7 +856,7 @@ struct PopoverView: View {
                         .font(.system(size: 11, weight: .medium))
                 }
                 .buttonStyle(.borderless)
-                .foregroundStyle(Color.razerGreen)
+                .foregroundStyle(Color.razerGreenText)
             }
         }
         }
@@ -992,7 +1022,7 @@ struct PopoverView: View {
         }
         .buttonStyle(.plain)
         .font(.system(size: 10.5, weight: active ? .semibold : .regular).monospacedDigit())
-        .foregroundStyle(active ? .white : .secondary)
+        .foregroundStyle(active ? Color.onRazerGreen : Color.secondary)
         .frame(maxWidth: .infinity)
         .frame(height: 24)
         .background(active ? Color.razerGreen : Color.primary.opacity(0.08),
@@ -1057,7 +1087,7 @@ struct PopoverView: View {
                     }
                     .buttonStyle(.plain)
                     .font(.system(size: 9.5, weight: Int(sleepTimeoutValue) == value ? .semibold : .regular).monospacedDigit())
-                    .foregroundStyle(Int(sleepTimeoutValue) == value ? .white : .secondary)
+                    .foregroundStyle(Int(sleepTimeoutValue) == value ? Color.onRazerGreen : Color.secondary)
                     .frame(maxWidth: .infinity).frame(height: 23)
                     .background(Int(sleepTimeoutValue) == value ? Color.razerGreen : Color.primary.opacity(0.08), in: RoundedRectangle(cornerRadius: 6))
                     .hoverHighlight(RoundedRectangle(cornerRadius: 6))
@@ -1103,7 +1133,7 @@ struct PopoverView: View {
         }
         .buttonStyle(.plain)
         .font(.system(size: 10.5, weight: active ? .semibold : .regular).monospacedDigit())
-        .foregroundStyle(active ? .white : Color.razerGreen)
+        .foregroundStyle(active ? Color.onRazerGreen : Color.razerGreenText)
         .frame(maxWidth: .infinity)
         .frame(height: 24)
         .background(active ? Color.razerGreen : Color.razerGreen.opacity(0.12),
@@ -1353,7 +1383,7 @@ struct PopoverView: View {
                         }
                     case .buttons:
                         Button { page = .buttons } label: {
-                            groupRowLabel(title: "Buttons", symbol: "keyboard", tint: .razerGreen,
+                            groupRowLabel(title: "Buttons", symbol: "keyboard", tint: .razerGreenText,
                                           value: buttonsSummary,
                                           valueColor: buttonsNeedAccess ? .batteryMid : .secondary,
                                           expanded: false)
@@ -1463,7 +1493,7 @@ struct PopoverView: View {
                     // Nothing at rest marks it as a link — the footer should stay quiet — so
                     // hover has to carry the whole affordance: colour and underline together,
                     // since colour alone is easy to miss at 11pt in tertiary grey.
-                    .foregroundStyle(versionHovered ? AnyShapeStyle(Color.razerGreen) : AnyShapeStyle(.tertiary))
+                    .foregroundStyle(versionHovered ? AnyShapeStyle(Color.razerGreenText) : AnyShapeStyle(.tertiary))
                     .underline(versionHovered)
             }
             .buttonStyle(.plain)
@@ -1476,7 +1506,7 @@ struct PopoverView: View {
                     .font(.system(size: 12.5))
                     // Same hover treatment as the version link beside it — a footer this
                     // quiet needs the cue, and two different ones would be noise.
-                    .foregroundStyle(gearHovered ? AnyShapeStyle(Color.razerGreen) : AnyShapeStyle(.secondary))
+                    .foregroundStyle(gearHovered ? AnyShapeStyle(Color.razerGreenText) : AnyShapeStyle(.secondary))
                     .contentShape(Rectangle())
             }
             .buttonStyle(.plain)
diff --git a/Sources/MacRazer/ProfilesView.swift b/Sources/MacRazer/ProfilesView.swift
index 2d737f9..421417e 100644
--- a/Sources/MacRazer/ProfilesView.swift
+++ b/Sources/MacRazer/ProfilesView.swift
@@ -82,7 +82,7 @@ struct ProfilesView: View {
                 Circle().fill(active ? Color.razerGreen : Color.primary.opacity(0.10))
                 if active {
                     Image(systemName: "checkmark").font(.system(size: 10, weight: .bold))
-                        .foregroundStyle(.white)
+                        .foregroundStyle(Color.onRazerGreen)
                 }
             }
             .frame(width: 20, height: 20)
diff --git a/Sources/MacRazer/RemapView.swift b/Sources/MacRazer/RemapView.swift
index 2849694..d5b2d1c 100644
--- a/Sources/MacRazer/RemapView.swift
+++ b/Sources/MacRazer/RemapView.swift
@@ -160,7 +160,7 @@ struct RemapView: View {
 
     private var detectionHint: some View {
         HStack(spacing: 8) {
-            Image(systemName: "cursorarrow.click.2").foregroundStyle(Color.razerGreen)
+            Image(systemName: "cursorarrow.click.2").foregroundStyle(Color.razerGreenText)
             if let b = remapper.lastDetectedButton {
                 Text("Detected: \(ButtonRemapper.label(for: b))")
                     .font(.system(size: 12, weight: .medium))
diff --git a/Sources/MacRazer/RemapWindowController.swift b/Sources/MacRazer/RemapWindowController.swift
index 71ed2f5..f53f4d2 100644
--- a/Sources/MacRazer/RemapWindowController.swift
+++ b/Sources/MacRazer/RemapWindowController.swift
@@ -27,6 +27,8 @@ final class RemapWindowController: AppWindowPresenter {
             w.title = "Configure Buttons"
             w.styleMask = [.titled, .closable, .miniaturizable]
             w.isReleasedWhenClosed = false
+            // Themed like the popover per Settings › Appearance, kept up to date when it changes.
+            AppearanceSettings.shared.track(w)
             w.center()
             window = w
         }
diff --git a/Sources/MacRazer/SettingsView.swift b/Sources/MacRazer/SettingsView.swift
index 4fba290..369918a 100644
--- a/Sources/MacRazer/SettingsView.swift
+++ b/Sources/MacRazer/SettingsView.swift
@@ -23,6 +23,7 @@ struct SettingsView: View {
     var onAutoInstallChanged: (() -> Void)?
     /// The crash window's "Don't Ask Again" writes the same key, so this is how to undo it.
     @AppStorage(CrashLogScanner.offerKey) private var offerCrashReports = true
+    @ObservedObject var appearance: AppearanceSettings = .shared
 
     var body: some View {
         VStack(alignment: .leading, spacing: 18) {
@@ -36,6 +37,10 @@ struct SettingsView: View {
                 // Hidden while there's nowhere to send a report; see `CrashReporting`.
                 if CrashReporting.isAvailable { crashReportsRow }
             }
+            titledSection("Appearance") {
+                themeRow
+                glassRow
+            }
             titledSection("Updates") {
                 autoInstallRow
                 versionRow
@@ -88,7 +93,7 @@ struct SettingsView: View {
             } else if launchAtLogin.needsApproval {
                 Button("Approve MacRazer in Login Items…") { launchAtLogin.openLoginItemsSettings() }
                     .buttonStyle(.plain).font(.system(size: 11))
-                    .foregroundStyle(Color.razerGreen)
+                    .foregroundStyle(Color.razerGreenText)
             }
         }
     }
@@ -111,6 +116,32 @@ struct SettingsView: View {
         )
     }
 
+    private var themeRow: some View {
+        VStack(alignment: .leading, spacing: 4) {
+            HStack {
+                Text("Theme").font(.system(size: 12.5, weight: .medium))
+                Spacer(minLength: 12)
+                Picker("Theme", selection: $appearance.theme) {
+                    ForEach(PopoverTheme.allCases) { Text($0.title).tag($0) }
+                }
+                .pickerStyle(.segmented)
+                .labelsHidden()
+                .controlSize(.small)
+                .fixedSize()
+            }
+            sectionNote("System follows macOS. Razer Green is always dark.")
+        }
+    }
+
+    private var glassRow: some View {
+        settingRow(
+            title: "Glass effect",
+            detail: "The popover and windows let the desktop show through. Turn it off for a solid "
+                + "background, which is easier to read over busy windows.",
+            isOn: $appearance.glass
+        )
+    }
+
     private var crashReportsRow: some View {
         settingRow(
             title: "Offer to send crash reports",
diff --git a/Sources/MacRazer/SettingsWindowController.swift b/Sources/MacRazer/SettingsWindowController.swift
index 66c7488..11f4128 100644
--- a/Sources/MacRazer/SettingsWindowController.swift
+++ b/Sources/MacRazer/SettingsWindowController.swift
@@ -41,8 +41,8 @@ final class SettingsWindowController: AppWindowPresenter {
             w.title = "MacRazer Settings"
             w.styleMask = [.titled, .closable]
             w.isReleasedWhenClosed = false
-            // Match the popover's forced-dark look so the green accent reads correctly.
-            w.appearance = NSAppearance(named: .darkAqua)
+            // Themed like the popover per Settings › Appearance, kept up to date when it changes.
+            AppearanceSettings.shared.track(w)
             w.center()
             window = w
         }
diff --git a/Sources/MacRazer/UpdatedView.swift b/Sources/MacRazer/UpdatedView.swift
index 8c1f7b0..1ef60c7 100644
--- a/Sources/MacRazer/UpdatedView.swift
+++ b/Sources/MacRazer/UpdatedView.swift
@@ -71,7 +71,7 @@ struct UpdatedView: View {
         } else {
             Link("Read the release notes on GitHub", destination: ProjectLinks.latestRelease)
                 .font(.system(size: 12, weight: .medium))
-                .foregroundStyle(Color.razerGreen)
+                .foregroundStyle(Color.razerGreenText)
         }
     }
 }
diff --git a/Sources/MacRazer/UpdatedWindowController.swift b/Sources/MacRazer/UpdatedWindowController.swift
index 88852be..a2a10c5 100644
--- a/Sources/MacRazer/UpdatedWindowController.swift
+++ b/Sources/MacRazer/UpdatedWindowController.swift
@@ -38,8 +38,8 @@ final class UpdatedWindowController: NSObject, AppWindowPresenter, NSWindowDeleg
             w.title = "MacRazer Updated"
             w.styleMask = [.titled, .closable]
             w.isReleasedWhenClosed = false
-            // Match the other windows: the green accent needs a dark ground.
-            w.appearance = NSAppearance(named: .darkAqua)
+            // Themed like the popover per Settings › Appearance, kept up to date when it changes.
+            AppearanceSettings.shared.track(w)
             w.delegate = self
             w.center()
             window = w
diff --git a/Sources/MacRazer/WhatsNewPage.swift b/Sources/MacRazer/WhatsNewPage.swift
index 5e09552..a8265c6 100644
--- a/Sources/MacRazer/WhatsNewPage.swift
+++ b/Sources/MacRazer/WhatsNewPage.swift
@@ -77,14 +77,14 @@ struct ReleaseNotesList: View {
                 if releases.count > 1 {
                     Text(release.version)
                         .font(.system(size: 12, weight: .semibold))
-                        .foregroundStyle(Color.razerGreen)
+                        .foregroundStyle(Color.razerGreenText)
                         .padding(.top, release.id == releases.first?.id ? 0 : 6)
                 }
                 notesBlock(release.notes)
             }
             Link("Full release notes", destination: ProjectLinks.latestRelease)
                 .font(.system(size: 11, weight: .medium))
-                .foregroundStyle(Color.razerGreen)
+                .foregroundStyle(Color.razerGreenText)
         }
         .frame(maxWidth: .infinity, alignment: .leading)
     }
diff --git a/Sources/MacRazer/main.swift b/Sources/MacRazer/main.swift
index b9adf5c..4894619 100644
--- a/Sources/MacRazer/main.swift
+++ b/Sources/MacRazer/main.swift
@@ -72,11 +72,10 @@ func openDevice() -> HIDDevice? {
 /// Shared by the render-* commands: draw a SwiftUI view at 2x on the app's dark backdrop
 /// and write it to a PNG.
 @MainActor func writeViewPNG<V: View>(_ view: V, to path: String) {
-    // Force dark, because every surface these previews stand in for does: the popover sets
-    // `.darkAqua`, and so do the Settings, Permissions and About windows. Without it
-    // `.secondary`/`.tertiary` resolve for light mode and render as near-black text on the
-    // dark backdrop below — which made every preview look like it had a contrast bug it
-    // doesn't have.
+    // Rendered in the Dark theme, to match the dark backdrop below. The app itself follows
+    // Settings › Appearance; without this `.secondary`/`.tertiary` resolve for light mode and
+    // render as near-black text on that backdrop, which made every preview look like it had
+    // a contrast bug it doesn't have.
     let renderer = ImageRenderer(
         content: view.environment(\.colorScheme, .dark).padding(1).background(Color(white: 0.13)))
     renderer.scale = 2
@@ -229,7 +228,8 @@ case "render-ui":
         : args.contains("profiles")
         ? AnyView(ProfilesView(controller: controller, remapper: ButtonRemapper(), onBack: {}))
         : AnyView(PopoverView(controller: controller, remapper: ButtonRemapper(), updateChecker: updateChecker,
-                              launchAtLogin: launchAtLogin, onOpenSettings: {},
+                              launchAtLogin: launchAtLogin, appearance: AppearanceSettings.shared,
+                              onOpenSettings: {},
                               onOpenDeviceTest: {})) // no windows in a render
     writeViewPNG(rootView, to: path)
 
diff --git a/Tests/MacRazerTests/PopoverThemeTests.swift b/Tests/MacRazerTests/PopoverThemeTests.swift
new file mode 100644
index 0000000..0eac703
--- /dev/null
+++ b/Tests/MacRazerTests/PopoverThemeTests.swift
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+// Part of MacRazer, a control app for Razer mice on macOS. See LICENSE and NOTICE.md.
+
+import XCTest
+import AppKit
+@testable import MacRazer
+
+final class PopoverThemeTests: XCTestCase {
+    /// Every theme × glass × system mode, against the table the mockups were approved from.
+    func testEveryCombinationResolvesToTheApprovedLook() {
+        let expected: [(PopoverTheme, Bool, Bool, PopoverLook)] = [
+            (.system, true, false, .lightGlass),
+            (.system, true, true, .darkGlass),
+            (.system, false, false, .solidLight),
+            (.system, false, true, .solidDark),
+            (.dark, true, false, .darkGlass),
+            (.dark, true, true, .darkGlass),
+            (.dark, false, false, .solidDark),
+            (.dark, false, true, .solidDark),
+            (.light, true, false, .lightGlass),
+            (.light, true, true, .lightGlass),
+            (.light, false, false, .solidLight),
+            (.light, false, true, .solidLight),
+            // Razer Green stays dark on a light Mac.
+            (.razerGreen, true, false, .greenGlass),
+            (.razerGreen, true, true, .greenGlass),
+            (.razerGreen, false, false, .solidGreen),
+            (.razerGreen, false, true, .solidGreen),
+        ]
+        XCTAssertEqual(expected.count, PopoverTheme.allCases.count * 2 * 2)
+        for (theme, glass, systemIsDark, look) in expected {
+            XCTAssertEqual(PopoverLook.resolve(theme: theme, glass: glass, systemIsDark: systemIsDark), look,
+                           "\(theme), glass \(glass), system dark \(systemIsDark)")
+        }
+    }
+
+    func testLookProperties() {
+        for look in PopoverLook.allCases {
+            XCTAssertEqual(look.appearanceName, look.isDark ? .darkAqua : .aqua)
+            // Plain glass keeps the native material; everything else paints over it.
+            let plainGlass = look == .lightGlass || look == .darkGlass
+            XCTAssertEqual(look.backdropColor == nil, plainGlass, "\(look)")
+            // A solid look must actually be solid, or the material shows through.
+            if !look.isGlass { XCTAssertEqual(look.backdropColor?.alphaComponent, 1, "\(look)") }
+        }
+        XCTAssertEqual(PopoverLook.allCases.filter(\.hasGreenEdge), [.greenGlass])
+        XCTAssertFalse(PopoverLook.lightGlass.isDark)
+        XCTAssertFalse(PopoverLook.solidLight.isDark)
+        XCTAssertTrue(PopoverLook.solidGreen.isDark)
+    }
+
+    @MainActor
+    func testSettingsDefaultAndPersist() throws {
+        let suite = "PopoverThemeTests.\(UUID().uuidString)"
+        let defaults = try XCTUnwrap(UserDefaults(suiteName: suite))
+        defer { defaults.removePersistentDomain(forName: suite) }
+
+        let settings = AppearanceSettings(defaults: defaults)
+        XCTAssertEqual(settings.theme, .system)
+        XCTAssertTrue(settings.glass)
+
+        settings.theme = .razerGreen
+        settings.glass = false
+        let reloaded = AppearanceSettings(defaults: defaults)
+        XCTAssertEqual(reloaded.theme, .razerGreen)
+        XCTAssertFalse(reloaded.glass)
+        XCTAssertEqual(reloaded.look(systemIsDark: false), .solidGreen)
+    }
+
+    @MainActor
+    func testUnknownStoredThemeFallsBackToSystem() throws {
+        let suite = "PopoverThemeTests.\(UUID().uuidString)"
+        let defaults = try XCTUnwrap(UserDefaults(suiteName: suite))
+        defer { defaults.removePersistentDomain(forName: suite) }
+
+        defaults.set("neon", forKey: AppearanceSettings.themeKey)
+        XCTAssertEqual(AppearanceSettings(defaults: defaults).theme, .system)
+    }
+
+    @MainActor
+    func testTrackedWindowsGetTheFullLook() throws {
+        let suite = "PopoverThemeTests.\(UUID().uuidString)"
+        let defaults = try XCTUnwrap(UserDefaults(suiteName: suite))
+        defer { defaults.removePersistentDomain(forName: suite) }
+
+        let settings = AppearanceSettings(defaults: defaults)
+        settings.applyToWindows(.solidLight)
+        let window = NSWindow(contentRect: NSRect(x: 0, y: 0, width: 200, height: 100),
+                              styleMask: [.titled], backing: .buffered, defer: true)
+        window.isReleasedWhenClosed = false
+        window.contentView = NSView()
+        // A window opened later takes the look the others already have.
+        settings.track(window)
+        XCTAssertEqual(window.appearance?.name, .aqua)
+        XCTAssertTrue(window.isOpaque)
+        XCTAssertEqual(window.backgroundColor, PopoverLook.solidLight.backdropColor)
+
+        settings.applyToWindows(.greenGlass)
+        XCTAssertEqual(window.appearance?.name, .darkAqua)
+        XCTAssertFalse(window.isOpaque)
+        XCTAssertEqual(window.backgroundColor, .clear)
+        let frameView = try XCTUnwrap(window.contentView?.superview)
+        let glass = try XCTUnwrap(frameView.subviews.compactMap { $0 as? NSVisualEffectView }.first)
+        XCTAssertFalse(glass.isHidden)
+        let tint = try XCTUnwrap(frameView.subviews.compactMap { $0 as? PopoverBackdropView }.first)
+        XCTAssertEqual(tint.fill, PopoverLook.greenGlass.backdropColor)
+
+        // Applying again reuses the same views rather than stacking new ones.
+        settings.applyToWindows(.solidDark)
+        XCTAssertEqual(frameView.subviews.compactMap { $0 as? NSVisualEffectView }.count, 1)
+        XCTAssertTrue(glass.isHidden)
+        XCTAssertNil(tint.fill)
+        XCTAssertEqual(window.backgroundColor, PopoverLook.solidDark.backdropColor)
+    }
+}
diff --git a/docs/DOCUMENTATION.md b/docs/DOCUMENTATION.md
index 5a91995..dd65702 100644
--- a/docs/DOCUMENTATION.md
+++ b/docs/DOCUMENTATION.md
@@ -230,7 +230,7 @@ A fixed **320*620** navigable container with three pages and a push/pop slide an
 page is a `ScrollView` (so long content scrolls without resizing the popover):
 
 - **Main page**, Control-Center-style frosted cards, each section its own tile:
- - **Header card**: Razer logo (bright green) in a tinted tile + detected device name +
+ - **Header card**: Razer logo (green) in a tinted tile + detected device name +
  connection state + status dot. Shows "No mouse connected" when none.
  - **Battery card**: a custom proportional **battery gauge** (fill tracks the exact %,
  colored green >=40% / orange <40% / red <15%), the big % number, a state-colored level
@@ -263,6 +263,26 @@ page is a `ScrollView` (so long content scrolls without resizing the popover):
  progress, where Esc cancels that).
  - Swatches, chips and the icon buttons carry VoiceOver labels and tooltips; chips and
  rows get a hover highlight.
+- **Appearance**, `PopoverTheme.swift`: Settings › Appearance has a **Theme** (System, Dark,
+ Light, Razer Green) and a **Glass effect** switch, stored as `appearance.theme` and
+ `appearance.glass` in UserDefaults. `PopoverLook.resolve` turns theme, glass and the system's
+ light or dark mode into one of six looks (light, dark or green glass; solid light #F5F5F7,
+ dark #1C1C1E or green #0F1A11). Razer Green is always dark.
+ - `AppDelegate` re-applies the look when the setting changes or macOS switches mode, including
+ while the popover is open. The popover's appearance is always set explicitly: a nil one would
+ follow the menu bar, which macOS tints from the wallpaper.
+ - Solid colours and the green tint are painted by `PopoverBackdropView`, which sits in
+ NSPopover's frame view just under the content. That view clips to the popover's outline, so
+ the fill covers the arrow too. A SwiftUI background would leave the arrow glass. The green
+ edge is a SwiftUI overlay on the body (radius 10, measured on macOS 26).
+ - Windows get the same look (`AppearanceSettings.track`, `WindowBackdrop`): glass is an
+ `NSVisualEffectView` with the popover's material, plus the same tint view, both in the
+ window's frame view so the title bar matches; solid looks set the window's background colour.
+ The title bar is transparent in every look. Only the popover gets the green edge.
+ - Colours: `razerGreen` is the fill (the same in both modes); text and icons use
+ `razerGreenText` (#23891A on light). Anything on a green fill uses `onRazerGreen`, a dark green,
+ because white on #44D62C is only about 1.9:1. `razerGreenBright` (logo) and `bluetoothBlue`
+ also adapt.
 - **Colour page**, `ColorPickerPage.swift`: an inline **hue/saturation colour wheel** +
  brightness slider + live preview, applied to the mouse live (throttled). Replaces the old
  system `NSColorPanel`.
@@ -366,6 +386,7 @@ that path draws the content but needs an explicit size, since there is no window
 | `RazerDevices.swift` | PID to {name, supported, hasBattery} registry. |
 | `BatteryHistory.swift` | Sample log + learned discharge rate + time estimate. |
 | `PopoverView.swift` | Main popover UI + page navigation. |
+| `PopoverTheme.swift` | Settings › Appearance: theme, glass, the resolved look, the popover and window backdrops. |
 | `ColorPickerPage.swift` | Inline hue/sat colour wheel page + shared `BackButton`. |
 | `ButtonRemapper.swift` | CGEvent tap, action model, presets, persistence, Accessibility. |
 | `RemapView.swift` | Button-config UI (inline + window), key recorder. |