de-emphasize display mode buttons on revision view

app/assets/stylesheets/desktop/history.scss

@@ -1,10 +1,7 @@
 // styles that apply to the popup that appears when you show the edit history of a post
 
 .modal.history-modal {
-  .btn {
-    // remove transitions on the buttons in the history modal
-    transition: none;
-  }
+
   .modal-inner-container {
     min-width: 960px;
     min-height: 500px;
@@ -21,6 +18,14 @@
   }
   #display-modes {
     text-align: right;
+    .btn {
+      background-color:inherit;
+      color: dark-light-diff($primary, $secondary, 50%, -50%);
+    }
+    .btn-primary {
+      color: $primary;
+      font-weight: bold;
+    }
   }
   #revision-details {
     padding: 5px;