Initial skeleton of multiple camera support.

src/scss/menu.scss

@@ -4,10 +4,15 @@
   --frigate-card-menu-button-size: 40px;
   --mdc-icon-button-size: var(--frigate-card-menu-button-size);
   --mdc-icon-size: calc(var(--mdc-icon-button-size) / 2);
-}
+  z-index: 10;
+  opacity: 0.9;
+
+  // Necessary to mitigate an apparent Chrome opacity flickering bug caused by
+  // button ripples.
+  will-change: opacity;
+ }
 
 .frigate-card-menu {
-  z-index: 1;
   /* Menu div itself does not handle click events. Without this, in overlay
      mode, the menu div prevents clicking on gallery items 'behind' the overlay.
      */
@@ -79,4 +84,4 @@
 .frigate-card-menu.full {
   width: 100%;
   background: var(--secondary-background-color);
-}
+}