code: function getImageSrcCSS(token) {
  	// A stylesheet token may contain either quoted ('string') or unquoted URL
  	let urlValue = token.item(0);
  	if (urlValue && urlValue.type === 'string') {
  		urlValue = urlValue.item(0);
  	}
  
  	return urlValue && urlValue.valueOf();
  }
docs: Returns image source from given `url()` token
  @param  {Token} token
  @return {String}