diff --git a/docs/changelog.rst b/docs/changelog.rst
index 97268e8..a1c923d 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -1,6 +1,14 @@
 Changelog
 =========
 
+Release 1.8
+-----------
+:released: unreleased
+
+* **Bugfix**: [#134] Improve support for external theme packages by using a ``get_scss_sources_path()`` convention.
+
+  - If needed, theme warnings can be suppressed via ``suppress_warnings = ["simplepdf.theme"]``.
+
 Release 1.7
 -----------
 :released: 02.12.2025
diff --git a/docs/configuration.rst b/docs/configuration.rst
index 233c40e..7cb01bd 100644
--- a/docs/configuration.rst
+++ b/docs/configuration.rst
@@ -166,7 +166,33 @@ simplepdf_theme
 ---------------
 .. versionadded:: 1.5
 
-Add custom theme for simplepdf. This overrides the default theme ``simplepdf_theme``
+Name of the theme to use for PDF output. This overrides the default theme ``simplepdf_theme``.
+The value must match both the Sphinx theme name and the importable Python module name.
+
+.. code-block:: python
+
+   simplepdf_theme = "my_custom_pdf_theme"
+
+The theme module must define a ``get_scss_sources_path()`` function that returns
+the absolute path to its SCSS sources directory. This is how the builder locates
+the SCSS files to compile into CSS for the PDF.
+
+**Minimal example:**
+
+.. code-block:: python
+
+   from os import path
+
+   def get_scss_sources_path():
+       """Return the absolute path to the SCSS sources directory."""
+       return path.join(path.abspath(path.dirname(__file__)), "static", "styles", "sources")
+
+The SCSS sources directory should contain a ``main.scss`` file as the entry point.
+You can use the bundled ``simplepdf_theme`` as a reference for the expected
+directory structure and SCSS files.
+
+.. note:: If the theme module cannot be imported or does not define ``get_scss_sources_path()``,
+   the builder falls back to the bundled ``simplepdf_theme`` SCSS sources and emits a warning.
 
 .. _theme_options:
 
diff --git a/pyproject.toml b/pyproject.toml
index e242d24..0735b33 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "flit_core.buildapi"
 
 [project]
 name = "sphinx-simplepdf"
-version = "1.7.0"
+version = "1.8.0"
 description = "An easy to use PDF Builder for Sphinx with a modern PDF-Theme."
 readme = "README.rst"
 license = "MIT"
diff --git a/sphinx_simplepdf/builders/simplepdf.py b/sphinx_simplepdf/builders/simplepdf.py
index 509b486..a88f943 100644
--- a/sphinx_simplepdf/builders/simplepdf.py
+++ b/sphinx_simplepdf/builders/simplepdf.py
@@ -1,3 +1,4 @@
+import importlib
 import os
 import re
 import subprocess
@@ -55,15 +56,7 @@ def __init__(self, *args, **kwargs):
         # Generate main.css
         logger.info("Generating css files from scss-templates")
         css_folder = os.path.join(self.app.outdir, "_static")
-        scss_folder = os.path.join(
-            os.path.dirname(__file__),
-            "..",
-            "themes",
-            "simplepdf_theme",
-            "static",
-            "styles",
-            "sources",
-        )
+        scss_folder = self._resolve_scss_folder()
         sass.compile(
             dirname=(scss_folder, css_folder),
             output_style="nested",
@@ -105,6 +98,34 @@ def get_theme_option_var(self, name, default):
             return default
         return simplepdf_theme_options[name]
 
+    def _resolve_scss_folder(self):
+        """Resolve the SCSS sources folder from the configured theme package.
+
+        Imports the theme module and calls its get_scss_sources_path(). Falls
+        back to the bundled simplepdf_theme if the theme cannot be imported or
+        does not define get_scss_sources_path().
+        """
+        theme_name = self.app.config.simplepdf_theme or "simplepdf_theme"
+        try:
+            theme_module = importlib.import_module(theme_name)
+            if hasattr(theme_module, "get_scss_sources_path"):
+                return theme_module.get_scss_sources_path()
+            logger.warning(
+                f"Theme '{theme_name}' does not define get_scss_sources_path(), "
+                "falling back to bundled simplepdf_theme",
+                type="simplepdf",
+                subtype="theme",
+            )
+        except ImportError:
+            logger.warning(
+                f"Could not import theme '{theme_name}', "
+                "falling back to bundled simplepdf_theme",
+                type="simplepdf",
+                subtype="theme",
+            )
+        from sphinx_simplepdf.themes.simplepdf_theme import get_scss_sources_path
+        return get_scss_sources_path()
+
     def finish(self) -> None:
         super().finish()
 
diff --git a/sphinx_simplepdf/themes/simplepdf_theme/__init__.py b/sphinx_simplepdf/themes/simplepdf_theme/__init__.py
index 8a873f5..bbc3bcd 100644
--- a/sphinx_simplepdf/themes/simplepdf_theme/__init__.py
+++ b/sphinx_simplepdf/themes/simplepdf_theme/__init__.py
@@ -14,6 +14,11 @@ def get_html_theme_path():
     return cur_dir
 
 
+def get_scss_sources_path():
+    """Return the absolute path to the SCSS sources directory."""
+    return path.join(path.abspath(path.dirname(__file__)), "static", "styles", "sources")
+
+
 # See http://www.sphinx-doc.org/en/stable/theming.html#distribute-your-theme-as-a-python-package
 def setup(app):
     app.add_html_theme("simplepdf_theme", path.abspath(path.dirname(__file__)))