add input styling for light and dark panels (leftpanel vs room header)

src/components/structures/GroupView.js

@@ -1287,6 +1287,7 @@ export default React.createClass({
 
             const headerClasses = {
                 mx_GroupView_header: true,
+                'light-panel': true,
                 mx_GroupView_header_view: !this.state.editing,
                 mx_GroupView_header_isUserMember: this.state.isUserMember,
             };