@jiangcaiyang It works if you do it right. It doesn't take LESS variables, but it does work. Odds are the less styles have higher specificity, so your custom CSS rules are not applied. Use !important or something instead. It will certainly benefit you to not be held back due to incompatibility with newer versions of NodeBB in the future.
Hmm, interestingly enough, it works on my site, you'll need to take everything in //convoe.com/vendor/convoe/_cnvo.register.js and make your own file and replace it, you don't really have to remove it completely. This is because I have hot-linking blocked as far as assets goes.