code: private static String getStyleClasses(Button button, boolean isResponsive) {
  		StringBuilder sb;
  		sb = new StringBuilder(40); // optimize int
  		sb.append("btn");
  		String size = button.getSize();
  		if (size != null) {
  			sb.append(" btn-").append(size);
  		}
  
  		String look = button.getLook();
  		if (look != null) {
  			sb.append(" btn-").append(look);
  		} else {
  			sb.append(" btn-default");
  		}
  
  		if (button.isDisabled()) {
  			sb.append(" disabled");
  		}
  		if (isResponsive) {
  			sb.append(" btn-block");
  		}
  		String sclass = button.getStyleClass();
  		if (sclass != null) {
  			sb.append(" ").append(sclass);
  		}
  
  
  		return sb.toString().trim();
  	}
docs: Collects the CSS classes of the button.
  
  @return the CSS classes (separated by a space).