I’ve created a new vault and copied some .css from my main vault.
I’ve enabled them under appearence, made sure they are actually a .css file and compared all settings i have on my main vault.
It could be a number of things: other snippets are needed in conjunction with these two, the themes or theme settings aren’t the same between vaults, a plugin could also be helping out in the main vault, and so on. Lots of moving parts