JOOMLA - Add Style Declaration

gistfile1.php

<?php if (!empty($attribs->select_banner_image)) { 
                 $style = 'html {
                 background-image: url('.$attribs->select_banner_image.') !important;
                 background-size: contain;
                 background-repeat: no-repeat;
                 background-position: center top;
             }';
             $doc->addStyleDeclaration( $style );
             } ?>