Since CSS is about the aesthetical layout of a web page, I guess it's easy to ask opinion based questions.
I guess that asking about reusability of some CSS code would not be opinion-based.
On the opposite side of the spectrum a question along the lines of is this layout nice? would be opinion based.
But I guess there are questions in the middle:
- Is this layout captivating?
- Does this layout prompt the user to continue navigate on the site?
- Does this layout attract CSS enthusiast because of its amazing tricks?
I would say that these are probably closer to be opinion-based than not.
On the other hand, making a website appearance nice is the target of CSS, so all idioms that this language uses must be based on objective, measurable properties. Better, they should be based on the measurable (at least in a statistical sense) relation between those properties/layouts that CSS allows and the reaction in the user.
And this makes me think some of those question are a little bit less opinion-based.
Is there any guidance in this sense?