Added styles for save button

common/lib/xmodule/xmodule/css/capa/display.scss

@@ -270,4 +270,10 @@ section.problem {
     border: 1px solid #ccc;
     padding: lh();
   }
+
+  section.action {
+    input.save {
+      @extend .blue-button;
+    }
+  }
 }