code: private static String getStyleClasses(AbstractNavLink link, boolean isResponsive) {
  		StringBuilder sb;
  		sb = new StringBuilder(20); // optimize int
  
  		String look = null;
  		if (link instanceof Link) {
  			look = ((Link) link).getLook();
  		} else if (link instanceof CommandLink) {
  			look = ((CommandLink) link).getLook();
  		}
  
  		if (look != null) {
  			sb.append("btn btn-").append(look);
  			if (isResponsive) {
  				sb.append(" btn-block");
  			}
  		}
  
  		return sb.toString().trim();
  	}
docs: Collects the CSS classes of the link.
  
  @return the CSS classes (separated by a space).