it takes a long time
You couldn't develop a good look without sharing time to it :-)
There are actually no prepared skins for miniBB. During years of development, CSS schema changed a lot and its contents, too. Since miniBB has been developed as a customized forum, I preferred to spend my time to create the basic CSS skin as simple to adjust as possible.
I've checked your forum and it looks balanced at the moment, maybe the font has to be changed to fit into white-on-dark theme. I personally do not prefer forums/websites with such themes. They are eyes-expensive, very difficult to read.
You could also post screenshots here if you'd like mention just a part of your work. Not everyone could recover tricked URLs :-) Like this would be better to show: