It doesn't necessarily need to be Turing complete, but CSS in its current form is harder to understand, debug or make sense of than most Turing-complete languages.
Do you mean because of how its designed to cascade, and all the details of priority that requires? Or something else?
Personally I've never found the language itself hard to understand other than issues where a style somewhere else bleeds in and I have to hope browser dev tools can point me in the right direction.
> Do you mean because of how its designed to cascade, and all the details of priority that requires? Or something else?
Mainly that. But there are other parts that feel clunkier than they need to be too, e.g. media queries force you to repeat yourself a lot when most of the time you just want to write an expression, before/after gives you a whole new way to write elements that's only used for this one niche thing. The language has these weirdly powerful individual features but weak general features and no overall cohesion.
> issues where a style somewhere else bleeds in and I have to hope browser dev tools can point me in the right direction.
The converse part is even worse IMO. There's no way to do any kind of "find usages", so you can never tell whether a given style is used or not. With the result that people never refactor or delete anything, and the codebase gets worse and worse.