$cssName

name of the widget the CSS of which you want to inherit for a custom widget

string $cssName;

Example

webix.protoUI({
    name:"myslider",
    $cssName:"slider webix_rangeslider",
    //other properties and methods
}, webix.ui.slider);
 
webix.ui({ view:"myslider"});

Details

By default, a custom widget inherits API of the widgets and mixins that are used for it, but not CSS.