How to add Icon in searchWidget

altair

I just want to add an icon in my searchWidget but i dont know how to 

 

just like this 

 

 

const searchWidget = new Search({

        includeDefaultSources: false,

        view: view,

      });

 

view.ui.add(searchWidget, { position: 'top-left', index: 0 });

 

the current design is