Many thanks for your help!
I thought instead of a plugin to a code that I enter there. The old code looked like this:
<style>
header, footer, #tertiary {display:none;}
#main {max-width: 1920px;}
#primary.content-area, #primary.site-content { width: 100%;}
.backButton {display:none !important;}
</style>
<script language=”JavaScript” type=”text/javascript”>
setTimeout(“location.href = ””,500000); // milliseconds, so 10 seconds = 10000ms
</script>
in the new theme, he just fades out the menu.
