Hi Richard,
Thank you for writing in, I just tested the tab element’s header on your page and it scrolls horizontally just fine, v2 tabs are designed that way. If you need the tabs header to stack on mobile, you can use the custom CSS provided here.
Please note that the custom CSS provided on that thread is only a guide and it would ultimately be your responsibility to take it from here.
There seems to be an issue on your Theme Options > CSS, please check it here and address the errors.
Hope it helps,
Cheers!