Changing width of the theme is fairly simple.
In style.css
Change following:
from
table#okvir
{
background-color: #FFFFFF;
width: 790px;
}
to
table#okvir
{
background-color: #FFFFFF;
width: 100%;
}
the defs to look at in style.css which control the over all look and feel of table rows for your entire site are called:
outer
head
even
odd
tr.even td
tr.odd td
Easiest way to determine what styles are assigned to page content on your site is to copy out the source of the page. Paste that code into a visual editor like Dreamweaver or GoLive then select rows and see what's assigned. (that's how I do it)
Keeping in mind that changing these style defs effects any modules you would install, or the default ones, on your site that also use those style defs. So you would be changing the entire site not just the Forum as you desire.
I have not looked at this particular style sheet in depth but it's very similiar to the others produced by 7Dana.com... each is very good cross browser.
regards
rocket98