Provide a smoother experience for iOS installs

[philschatz]

See https://www.netguru.com/codestories/few-tips-that-will-make-your-pwa-on-ios-feel-like-native

specifically, something like this to make the popup point to the button in safari:

.popup-pointer {
    display: block;
    position: absolute;
    content: "";
    width: 10px;
    height: 10px;
    right: -10px;
    bottom: 10px;
    background-color: inherit;
    transform: translateX(-6px) rotate(45deg);
    pointer-events: none;
}