feat: Add richer card theme support (#1809)

src/scss/submenu.scss

@@ -7,3 +7,14 @@
 mwc-list-item {
   z-index: 20;
 }
+
+ha-icon-button {
+  // The main submenu icon is expected to follow Frigate card theming unless it
+  // is are active (in which case we want to take advantage of the whatever
+  // styling is appropriate, e.g. light icon partially lit).
+  --state-unavailable-color: var(--frigate-card-button-color);
+  --state-inactive-color: var(--frigate-card-button-color);
+
+  color: var(--frigate-card-menu-button-inactive-color);
+  background-color: var(--frigate-card-menu-button-background);
+}