$cssName

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

string $cssName;

Example

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

Details

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