gistfile1.txt

<?php
/**
 * Plugin Name: Custom CSS for wp-impress-js
 */
 
add_action( 'impress_head', 'mask_custom_css_for_wp_impress_js' );

function mask_custom_css_for_wp_impress_js() {
?>
<style>
header { z-index: 0 !important; }
</style>
<?php
}