how to change background color of google vr view fullscreen icon?

Question

This is an image you see a full-screen icon

window.addEventListener('load', onVrViewLoad);

      function onVrViewLoad() {
        var vrView = new VRView.Player('#vrview', {
          image: 'https://cors-anywhere.herokuapp.com/http://d305uc8ofhou21.cloudfront.net/images/vrimage/vr_kitchen.jpg',
          width:'500px',
          height:'300px'});
      }

<div id="vrview" class="view-image"></div>