Disable focus state borders.

Since we will be adding more interactivity, the active state will
eventually pop the menu open, so I'm not worried about accessibility of
this right now.

src/components/asset-button/asset-button.css

@@ -11,6 +11,8 @@
     border-radius: 100%;
     width: 2.75rem;
     height: 2.75rem;
+    outline: none;
+    border: none;
 }
 
 .icon {