Enforce rounded corners only on Adwaita theme

Adwaita does not have rounded corners yet, but will have soon. Enforce rounded corners in the app only for Adwaita to avoid bumping min required GTK version.

css/styles.css

@@ -18,6 +18,18 @@ radio {
 .gtk402 .osd trough highlight {
   border-color: inherit;
 }
+.adwrounded.csd {
+  border-radius: 8px;
+}
+.adwrounded.fullscreen,
+.adwrounded.maximized,
+.adwrounded.tiled,
+.adwrounded.tiled-top,
+.adwrounded.tiled-left,
+.adwrounded.tiled-right,
+.adwrounded.tiled-bottom {
+  border-radius: 0px;
+}
 
 .tvmode popover box {
   text-shadow: none;

src/appBase.js

@@ -95,6 +95,12 @@ class ClapperAppBase extends Gtk.Application
         const theme = gtkSettings.gtk_theme_name;
         debug(`user selected theme: ${theme}`);
 
+        if(
+            theme.startsWith('Adwaita')
+            && !this.active_window.has_css_class('adwrounded')
+        )
+            this.active_window.add_css_class('adwrounded');
+
         if(!theme.endsWith('-dark'))
             return;