Custom Widget Classes helps to set different css class or styles for widgets,the css class or styles can show in a dropdown list to be choosed . the list of css classes can be added from backend and also can code with theme. see the options at settings>>widget classes and add classes. If you are a theme developer you can add the classes in theme itself add this code add_filter('cWCdeveloperClasses','widgetclasses'); function widgetclasses(){ $clsses['classes']= array( array( 'class'=>'with-border', 'desc'=>'With Border' ), array( 'class'=>'white-bg', 'desc'=>'white background' ) ); return $clsses; } if you want to set a default one for all the newly added widgets,add the default class too as shown below add_filter('cWCdeveloperClasses','widgetclasses'); function widgetclasses(){ $clsses['classes']=array( array( 'class'=>'with-border', 'desc'=>'With Border' ), array( 'class'=>'white-bg', 'desc'=>'white background' ) ); $clsses['default']=array( 'class'=>'widget', 'desc'=>'Widget' ); return $clsses; }