// preload css in wordpress
// add this code in child theme function.php
add_filter( 'style_loader_tag',  'preload_css', 10, 2 );

function preload_css( $html, $handle ){

    $targetHanlde = array('zuhaus_mikado_child_style');

    if( in_array( $handle, $targetHanlde ) ){

        $html = str_replace("rel='stylesheet'", "rel='preload'", $html);
    }

    return $html;
}