animated active tab border: apply mask-image to the background-color

This fixes #488

chrome/tab_animated_active_border.css

@@ -21,9 +21,11 @@ See the above repository for updates as well as full license text. */
     hsl(240 100% 65%) 255deg,
     hsl(300 100% 60%) 290deg,
     hsl(360 100% 70%) 360deg);
+  mask-image: url("data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciPg0KICA8cmVjdCB4PSIwIiB5PSIwIiByeD0iNCIgc3Ryb2tlPSJyZWQiIHdpZHRoPSIxMDAlIiBoZWlnaHQ9IjEwMCUiIHN0cm9rZS13aWR0aD0iMiIgZmlsbD0ibm9uZSIgdmVjdG9yLWVmZmVjdD0ibm9uLXNjYWxpbmctc3Ryb2tlIi8+DQo8L3N2Zz4");
   background-size: cover;
   background-position: center;
   animation: filter steps(30) 2s infinite;
+  
 }
 .tab-background[selected]{
   border: 1px solid transparent !important;