Vertical scroll on tab contents: doesn't work on mobiles

I realize this plugin isn’t being supported anymore, but maybe someone can answer this anyway. I’m trying to get the contents of the tab to scroll vertically on mobile devices. I can get it to scroll on desktops by adding this to the css:
#tab_slide {overflow-y: scroll;}
But when I do this, the tab button simply vanishes from mobile devices.
You can check out my test of this here: nexus.universaltheosophy.com

I’m assuming this is some kind of problem with the “position” of the tab? i.e. position:absolute or position:fixed is perhaps screwing with the mobile display??

Anyway, any help would be hugely appreciated.

Alternately, if anyone knows of another good (free) plugin to accomplish this, please let me know. I’ve searched far and wide and all the free ones I could find were broken or unsupported etc. My main requirement is the use of widgets in the tab content area.

Thanks folks.

https://www.ads-software.com/plugins/tab-slide/