Gtk-4: Add initial suppport to gtk v4

gtk-4.0/widgets/_progress-bars.scss

@@ -0,0 +1,56 @@
+/*****************
+ * Progress bars *
+ *****************/
+progressbar {
+  // sizing
+  &.horizontal {
+    trough,
+    progress { min-height: 6px; }
+  }
+
+  &.vertical {
+    trough,
+    progress { min-width: 6px; }
+  }
+
+  &.horizontal progress { margin: 0;} // the progress node is positioned after the trough border
+  &.vertical progress { margin: 0; @include scale-highlight(bottom);}   // this moves it over it.
+
+
+  // FIXME: insensitive state missing and some other state should be set probably
+  font-size: smaller;
+  color: transparentize($fg_color, 0.6);
+
+  &:backdrop {
+    box-shadow: none;
+    transition: $backdrop_transition;
+  }
+
+  trough { @extend %scale_trough; }
+
+  &:backdrop trough { @extend %scale_trough:backdrop; } // looks like states are not passed to the trough component here
+
+  progress {
+    @extend %scale_highlight;
+  }
+
+  &:backdrop progress { @extend %scale_highlight:backdrop; } // states not passed here as well
+
+  &.osd { // progressbar.osd used for epiphany page loading progress
+    min-width: 3px;
+    min-height: 3px;
+    background-color: transparent;
+
+    trough {
+      border-style: none;
+      border-radius: 0;
+      background-color: transparent;
+      box-shadow: none;
+    }
+
+    progress {
+      border-style: none;
+      border-radius: 0;
+    }
+  }
+}