yy1993

This great article by Chris Coyier should help you understand some of the differences.
 
As for the white line, it depends on the operating system, as well as browser client/version.
 
To achieve the Open Atrium look, try adding more padding, and reducing the border radius to ~5px.

Change code to this:
 

body { font-family: Helvetica Neue, Helvetica, Arial; color: #ffffff; font-size: 14px; background: #1f1f1f; } a:link, a:active, a:visited { text-decoration: none; color: #ffffff; } a:hover { text-decoration: underline; color: #ffffff; } .top-menu { width: 1260px; margin: 0 auto; } /* Navigation */ .nav { float: left; display: block; margin-top: 20px; } .nav li { display:inline; } .nav li a { color: #fffff; padding: 0px 10px; margin-right: 25px; display: block; float: left; font-size: 16px; text-align: center; } .nav li a:hover, .nav li a.selected { color: #5e5e5e; text-decoration: none; } .nav li a.selected { background: transparent; border: 1px solid #ffffff; -moz-border-radius: 10px; } #footer { clear: both; font-size: 12px; text-align: center; color: #5e5e5e; }

1. A mobile site is normally less UI based, little graphics, and the screen size is optimised for browsers so using fluid widths.
2. There is no set width / height as all mobile devices are different, just use a fluid width
3. Yes it's done via html/css
4. I would build the mobile site e.g. mobile.domain.com or domain.com/mobile then include in the header, a function that detects a mobile and directs them to the mobile site.
 
One method is via php - http://detectmobilebrowsers.mobi/

Not sure whether it's for me to say, but some people may not know how to use the rating system on the new forum, and I haven't seen any threads explaining how to do so.
 
You may have noticed that at the bottom right of every single post, there's a + and - sign, that will have a '0' in when it's first posted, if you press +, it'll go to '1', and if you press - it'll go to '-1' (assuming that nobody has pressed it), by doing this, it affects the rating of individuals in their profile, which can be viewed by clicking their username by the side of their posts, in the thread title etc.
 
How you should see it is a thanks system, similar to those on other boards powered by vBulletin, so every time you see a helpful post, you give it a +, if you see a negative, unfriendly post, give it a -, this should help to deter individuals from saying bad things or spamming, and encourage people to help, which is always the best thing for this forum.