[Dead Eddie]

create a new file in core/vb/api called apheadcheck.php

within that file, add this code:

PHP Code:

class vB_Api_Apheadcheck extends vB_Api
{

    protected $disableWhiteList = array('headcheck');
    
    /**
    * @return boolean
    **/
    public function headcheck()
    {
        //insert your code here
        //should return true/false
    }

} 


Make sure your code returns a true/false, you can then call it (as above), and use the variable to decide if you want to include your custom css or not.

(warning...untested)