Move the overlay color back to the button base styles.

Author: crisbeto

src/lib/button/_button-theme.scss

@@ -80,12 +80,6 @@
     background-color: md-color($accent);
     color: md-color($accent, default-contrast);
   }
-
-  .md-button-focus-overlay {
-    @include md-high-contrast {
-      background-color: if(map_get($theme, is-dark), rgba(black, 0.5), rgba(white, 0.5));
-    }
-  }
 }
 
 

src/lib/button/button.scss

@@ -80,6 +80,13 @@
   border-radius: inherit;
   pointer-events: none;
   opacity: 0;
+
+  @include md-high-contrast {
+    // Note that IE will render this in the same way, no
+    // matter whether the theme is light or dark. This helps
+    // with the readability of focused buttons.
+    background-color: rgba(white, 0.5);
+  }
 }
 
 // For round buttons, the ripple container should clip child ripples to a circle.