Bug 1736437 - Port bug 1509931: Simplify titlebar buttons CSS. r=aleca

There's no need to use the media query to set the default styles of the
buttons, we only need to hide them if appropriate.

--HG--
extra : amend_source : 9b3384e4e63509de8d5ba1be1b29e95ed049335b

mail/themes/linux/mail/messenger.css

@@ -77,17 +77,9 @@
 
 /* We draw to titlebar when Gkt+ CSD is available */
 @media (-moz-gtk-csd-available) {
-  /* Some Gtk+ themes use non-rectangular toplevel windows. To fully support
-   * such themes we need to make toplevel window transparent.
-   * It may cause performanance issues so let's put it under a preference
-   * and enable it for desktop environment which do that by default.
-   * See nsWindow::TopLevelWindowUseARGBVisual() for details. */
-  @media (-moz-gtk-csd-transparent-background) {
-    :root[tabsintitlebar]:not(:-moz-lwtheme) {
-      background-color: transparent;
-      background-image: linear-gradient(transparent 25px, -moz-dialog 25px);
-      appearance: none;
-    }
+  :root[tabsintitlebar]:not(:-moz-lwtheme) {
+    background-color: transparent;
+    background-image: linear-gradient(transparent 25px, -moz-dialog 25px);
   }
 
   :root[tabsintitlebar] #titlebar:-moz-lwtheme {
@@ -153,42 +145,34 @@
   }
 
   /* Render titlebar command buttons according to system config.
-   * Use full scale icons here as the Gtk+ does.
-   */
-  @media (-moz-gtk-csd-minimize-button) {
-    #titlebar-min {
-      appearance: auto;
-      -moz-default-appearance: -moz-window-button-minimize;
-    }
+   * Use full scale icons here as the Gtk+ does. */
+  #titlebar-min {
+    appearance: auto;
+    -moz-default-appearance: -moz-window-button-minimize;
   }
+  #titlebar-max {
+    appearance: auto;
+    -moz-default-appearance: -moz-window-button-maximize;
+  }
+  :root[sizemode="maximized"] #titlebar-max {
+    appearance: auto;
+    -moz-default-appearance: -moz-window-button-restore;
+  }
+  #titlebar-close {
+    appearance: auto;
+    -moz-default-appearance: -moz-window-button-close;
+  }
+
   @media (-moz-gtk-csd-minimize-button: 0) {
     #titlebar-min {
       display: none;
     }
   }
-
-  @media (-moz-gtk-csd-maximize-button) {
-    #titlebar-max {
-      appearance: auto;
-      -moz-default-appearance: -moz-window-button-maximize;
-    }
-    :root[sizemode="maximized"] #titlebar-max {
-      appearance: auto;
-      -moz-default-appearance: -moz-window-button-restore;
-    }
-  }
   @media (-moz-gtk-csd-maximize-button: 0) {
     #titlebar-max {
       display: none;
     }
   }
-
-  @media (-moz-gtk-csd-close-button) {
-    #titlebar-close {
-      appearance: auto;
-      -moz-default-appearance: -moz-window-button-close;
-    }
-  }
   @media (-moz-gtk-csd-close-button: 0) {
     #titlebar-close {
       display: none;