Whatever you do Sektor
, please do not upgrade to crap looking phpbb latest or something like that on pic:
This old default style you use atm, is nice, it's clear, it has good colors, style etc, and it does it's job perfectly and it is good for eyes.
All the mods by Cuban-Pete is suggesting are also fine.
But just tell you, do not upgrade to it.
I my opinion, it looks horrible
Many good forums just updated their software (mostly to vBulletin new version) and they look very bad now, even some forums in Estonia, i rarely even visit them now.
They hurt eyes and are very hard to read now.
If you must, then at least leave an option for users to use old one.