Remove Flash of Unstyled Content in WordPress using SiteOrigin Page Builder and Mega Menu

functions.php

<?php

function head_fouc_script() {
?>
<script>
document.body.style.setProperty("visibility", "hidden", "important");
</script>
<style>
#mega-menu-wrap-primary #mega-menu-primary { /* these IDs may differ depending on the name of your menu. */
  visibility: inherit; /* mega menu sets visibility visible and shows if you don't set this */
}
</style>
<?php
}
add_action( 'genesis_before', 'head_fouc_script', 1 );

function footer_fouc_script() {
?>
<script>
// loadScript(scriptUrl): checks if a script has loaded yet
function loadScript(scriptUrl) {
  const script = document.createElement('script');
  script.src = scriptUrl;
  document.body.appendChild(script);
  
  return new Promise((res, rej) => {
    script.onload = function() {
      res();
    }
    script.onerror = function () {
      rej();
    }
  });
}

var mega_menu_script = '<?php echo plugins_url() .'/megamenu/js/maxmegamenu.js'; ?>';
var siteorigin_script = '<?php echo plugins_url() .'/siteorigin-panels/js/styling.min.js' ?>';

loadScript(mega_menu_script).then(() => {
	console.log('mega menu script loaded');
	loadScript(siteorigin_script).then(() => {
		console.log('siteorigin script loaded');
		document.body.style.setProperty("visibility", "visible");
	}).catch(() => {
		console.log('error, script loading failed');
	});
}).catch(() => {
	console.log('error, script loading failed');
});


</script>
<noscript><style>body { visibility: visible !important; }</style></noscript>
<?php
}
add_action( 'admin_footer', 'footer_fouc_script', 100 );
add_action( 'wp_footer', 'footer_fouc_script', 100 );

?>