Bug 1974861 - Improve titlebar in Adwaita / Yaru by providing a button background. r=stransky

Differential Revision: https://phabricator.services.mozilla.com/D256181

Author: emilio

browser/themes/linux/browser.css

@@ -208,6 +208,11 @@
     height: 24px;
     /* Matches the libadwaita transition */
     transition: background-color 0.2s ease;
+
+    @media (-moz-gtk-theme-family: adwaita) or (-moz-gtk-theme-family: yaru) {
+      /* On Adwaita / Yaru, the titlebar buttons have a background by default */
+      background-color: color-mix(in srgb, currentColor 10%, transparent);
+    }
   }
 
   &:hover > .toolbarbutton-icon {

widget/gtk/nsLookAndFeel.cpp

@@ -2144,10 +2144,11 @@ void nsLookAndFeel::PerThemeData::Init() {
   mName = GetGtkTheme();
 
   mFamily = [&] {
-    if (mName.EqualsLiteral("Adwaita") || mName.EqualsLiteral("Adwaita-dark")) {
+    if (StringBeginsWith(mName, "Adw"_ns)) {
+      // This catches "Adwaita", "Adwaita-dark", and "Adw-gtk3" too.
       return ThemeFamily::Adwaita;
     }
-    if (mName.EqualsLiteral("Breeze") || mName.EqualsLiteral("Breeze-Dark")) {
+    if (StringBeginsWith(mName, "Breeze"_ns)) {
       return ThemeFamily::Breeze;
     }
     if (StringBeginsWith(mName, "Yaru"_ns)) {