feat: Answer or reject inbound calls from menu (#2620)

- For: #2587

src/scss/menu.scss

@@ -141,3 +141,19 @@ div.opposing {
 
 // Further theme related styling is dynamically applied by `menu.ts`, see
 // `_renderPerInstanceStyle`.
+
+/*****************
+ * Pulse animation
+ *****************/
+
+// Referenced by the inline `animation` on emphasized button styles in
+// `menu-button-controller` (e.g. the ringing call button).
+@keyframes pulse {
+  0%,
+  100% {
+    opacity: 1;
+  }
+  50% {
+    opacity: 0.5;
+  }
+}

src/scss/themes/base.scss

@@ -105,6 +105,11 @@
     var(--advanced-camera-card-warning-color)
   );
 
+  // The color of a positive icon in the menu (e.g. answer an inbound call).
+  --advanced-camera-card-menu-button-positive-color: var(
+    --advanced-camera-card-success-color
+  );
+
   // The background color of the button "circles" in the menu.
   --advanced-camera-card-menu-button-background: color-mix(
     in oklab,