Looking for slide down onclick menu html5 template

I am looking for an html5 template that functions much like this (Drupal) site: https://www.kronos.com. Specifically, I need a menu that when clicked, it opens a submenu that pushes the rest of the page content down and provides an extensive submenu area, like the Kronos page is. I’ve ran into issues hand coding and combining different code, so am hoping to find a template I can use to jump off. Does any like this exist? Thanks!

I could provide a custom work, if you’re interested in

This is a bootstrap menu customization.
I can get it done for you.
My HTML template is Stanza Store HTML template

You will not find this menu in the above template but I can get it done for you at a minimal cost.