Mispunt: I wanted to give a bold font to the subtitles on the menu . For that alone i had to spend more than half an hour studying how the design worked.
If the design FORCES me to spend a lot of time just to change a TINY detail, then it's flawed from the beginning.
If I understand the change you're talking about, all you did was insert some <b> tags around the static text "modules", "support", and "others".
That's not using CSS at all; rather it is very basic HTML. If you wanted to implement a CSS solution, it would have been simple enough to copy the the definition for ".pn-title", downsize the font one pixel, and rename it to ".pn-bold". In the HTML, placing a <font class="pn-bold"></font> around the appropriate text would then apply the desired effect.
Having a separate definition named that might be counter-beneficial; something along the lines of "pn-subtitle" or such probably would be more helpful.
I choose to stay with the current design and only change (by applying small patches) "the necessary", we might end up with a website that could barely be maintained (in the best case).
In my opinion, the flaws in the existing design have absolutely nothing to do with the cascading style sheet. In fact, many web designers these days would not work without them. The problem often lies in more of a ignorance of what CSS can do (and making an effective implementation), I feel.
For example, the HTML clearly shows many table definitions. Tables are quite redundant (unnecessary) if one is using CSS. Content can be organized into rectangular blocks (the same concept as tables) in CSS, but with much greater simplicity than those nested definitions that HTML tends to require.
The readibility of the internal HTML definitions would be much improved if they maximized their usage of CSS.
Also, I've noticed some PHP usage throughout the site (besides the forum, which is obviously some variant of phpBB). The sidebar links, however, seem to be statically written into each page of the site. With PHP available, this can be avoided. In the simplest case, you can use PHP to insert the shared information from a seperate file. With that method, the sidebar's content would only be written once, in a single file. Modify it just once there, and the changes automatically apply to all pages which import that same content (which literally seems to be every page).
The formatting of the actual page definitions could use some more consistent structure, though that still has part to do with the use of HTML tables.