make volume bar gray if muted

resources/style.css

@@ -44,6 +44,10 @@ toolbarview#main {
   min-height: 15px;
 }
 
+.mute #volume-scale trough highlight {
+  background-color: oklch(from var(--accent-bg-color) l 0% h);
+}
+
 #play-queue listview {
   background-color: rgba(0,0,0,0);
 }

src/ui/window.rs

@@ -477,6 +477,12 @@ mod imp {
 
         fn set_mute(&self, mute: bool) {
             self.mpv.set_property("mute", mute).unwrap();
+
+            if mute {
+                self.obj().add_css_class("mute");
+            } else {
+                self.obj().remove_css_class("mute");
+            }
         }
 
         fn pause(&self) -> bool {