Post the link to your NodeBB forum and rate the forum of the previous user.
You can give a score of 1. very bad to 10. the best.
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What do you think of my forum
I use a dark (black and yellow) persona theme. I removed the profile pictures and make most of the images square with round edges.
You probably need to be more specific with your rule selector (the 'a' part). If another rule is more specific, it will overwrite yours. Examples:
An 'a' tag with a class: a.someclass
An 'a' tag as the child of a 'div' tag: div > a
An 'a' tag after a tag with an id: #someid + a
If any of such rules exist, they will overwrite yours. You can see what rules are active in most browsers by right-clicking something and choosing 'Inspect'
Other things: Make sure the little checkbox 'Use Custom CSS' below is checked. Try restarting nbb and clearing your browser cache if nothing else works.