redo button styles

- rename .btn-bs to .btn-bd-purple
- abstract yellow masthead button into .btn-bd-yellow and use it the new
docs navbar

assets/scss/_buttons.scss

@@ -2,16 +2,28 @@
 //
 // Custom buttons for the docs.
 
-.btn-bs {
+.btn-bd-purple {
   font-weight: 500;
   color: $bd-purple-bright;
   border-color: $bd-purple-bright;
 
   &:hover,
-  &:focus,
   &:active {
     color: #fff;
     background-color: $bd-purple-bright;
     border-color: $bd-purple-bright;
   }
 }
+
+.btn-bd-yellow {
+  font-weight: 500;
+  color: $bd-yellow;
+  border-color: $bd-yellow;
+
+  &:hover,
+  &:active {
+    color: $bd-graphite;
+    background-color: $bd-yellow;
+    border-color: $bd-yellow;
+  }
+}

assets/scss/_masthead.scss

@@ -36,15 +36,6 @@
     padding: 1rem 2rem;
     font-size: 1.25rem;
     font-weight: 500;
-    color: $bd-yellow;
-    border-color: $bd-yellow;
-
-    &:hover,
-    &:focus {
-      color: $bd-graphite;
-      background-color: $bd-yellow;
-      border-color: $bd-yellow;
-    }
   }
 
   .carbonad {