solid background for helios key binding helper

css/helios.css

@@ -536,6 +536,7 @@ body[id="helios"] .key_helper .command strong {
 body[id="helios"] .key_helper #binding-helper-main {
   display: block;
   padding: 5px;
+  background: #eee;
 }
 body[id="helios"] .key_helper .label {
   padding: 1px 4px;

css/helios.less

@@ -617,6 +617,7 @@ body[id="helios"] {
 		#binding-helper-main {
 			display: block;
 			padding: 5px;
+			background: #eee;
 		}
 
 		.label {