I have this plugin: http://mmenu.frebsite.nl/
It's implemented here: http://ultiuscorp.com/sodemo/demo/horizontal-submenus.html
The only thing I added was making the header fixed.
In iOS7/Safari or Chrome: But, when I am scrolled down and then close the menu there is a "flash" of black and I don't know how to remove it. You can't really see it on a desktop but it's painful to use it on my iPhone.
I have experimented with different z-index levels for each element (like the similar question here How can I fix the image "flashing" that occurs on my site when I open the mmenu menu?) but it was no help.
This issue even happens on the demo page for the plugin itself.
Any thoughts?