_background-variant.scss in bootstrap-4.0.0.beta3

- old
+ new

@@ -4,10 +4,11 @@
 
 @mixin bg-variant($parent, $color) {
   #{$parent} {
     background-color: $color !important;
   }
-  a#{$parent} {
+  a#{$parent},
+  button#{$parent} {
     @include hover-focus {
       background-color: darken($color, 10%) !important;
     }
   }
 }