Was curious if there was a .css trick to use to enable the sticky header in mobile view. Currently, it only works on the desktop view by default.
Unfortunately, not that I know of. In all honesty, I may not recommend making the mobile menu sticky as it would cover a good portion of the screen and depending on how long the menu was, it would make reading content on a mobile device really difficult. It is possible with some custom CSS I would imagine, but you would have to do quite a bit of re-working to get it looking the way you would want it to ensure a smooth user experience.