Rowan, http://www.ganonbaker.com is HelloMix?
Anyway, we can’t give support for custom changes.
If you look, the theme works properly on the demo, also you can see that tabs working fine. The demo is the same file you downloaded. If you change it, we can give you some help, but no more.
If you can’t solve it by your self, we have custom service to can help you.
I wish you understand.