Tags adjusted as requested by OP.

journalofavegan One idea is go to Core’s Less folder. Take the most common CSS/Less out of there. Paste into admin appearance custom CSS box. Start making small changes. Check each change often in at least two different browsers.

https://github.com/flarum/core/tree/master/less/forum

It will be very time consuming especially if you’ve never worked with CSS. But, because it is time consuming, that’s why most won’t do it for free.

    010101 Thank you. I wasn't waiting for something from the scratch, I was wondering if anyone did it already, might help me too.