// Random background image that changes on page refresh for Front Page 1
add_action( 'wp_head', 'sk_front_page_1_background_image' );
function sk_front_page_1_background_image() {

    // abort if Soliloquy is not active
    if ( ! function_exists( 'soliloquy' ) ) {
        return;
    }

    // "display" Front Page 1 slider - i.e., get the URL of random slide image using the soliloquy_output filter used earlier and store it in a variable
    $random_slide_image_url = soliloquy( 'front-page-1', 'slug', array(), true  );

    if ( $random_slide_image_url ) { ?>
        <style type="text/css">
            .front-page-1 {
                background-image: url(<?php echo $random_slide_image_url; ?>);
            }
        </style>
    <?php }
}