XF 2.1 Remove style choice for guests

[Jon12345]

I have a default theme and a dark theme for my forum. Is it possible to remove that choice from guest visitors? I've looked but can't work out how!

 

[Kirby]

Do you want guests to not be able to use Styles other than the default Style?
This does require custom PHP code.

Or do you just want to remove the option to choose another style?
This can be done by modifying the template or even with a CSS rule to hide the chooser.

 

[Jon12345]

I have a problem with guests being shown both dark theme and light theme due to a litespeed cache, possibly. So therefore, I was thinking if no guest has an option of the dark theme, maybe that would stop this. But I don't know. Maybe I am wrong.