Altering comment layout – DarkNight 2 theme

I had a search and found various things which I’ve tried, but nothing seems to be working.

I setup a new site with the DarkNight 2.0 theme, which is working great and I’ve been able to edit to my hearts content so far, but editing the comments is proving more troublesome.

The page in question is http://www.cornwalltangsoodo.co.uk/vipersquad/

If you notice between each post there’s a nice dotted line, and I have the css for this and want to add it (possibly using the other border- attributes top, left and right) to the comments when viewing comments. If you look at a page with comments such as http://www.cornwalltangsoodo.co.uk/vipersquad/?p=10#comments the comments are hard to pick out from one another. That’s why I want to box them out in some way.

I’ve had a look at the source of the generated page, and notcied that it uses a couple of classes in the <div> declarations, the one which goes around the comment header and body of text seems to be called commentbox.

In the style.css the theme uses, there seems to be no commentbox class. I tried adding one with

#commentbox {
margin:.5em 0 1.5em;
border-top:1px dotted #444;
border-left:1px dotted #444;
border-right:1px dotted #444;
border-bottom:1px dotted #444;
padding-bottom:1.5em;
}

but nothing happens. I also tried renaming the class to commentinfo, which is what the body of the comment text uses, but to no avail. Any ideas?