The multi button classes are .left, .middle and .right. With their usage being self evident.
This is a simple set of pre-made but extensible CSS3 buttons available in several different colours, configurations or sizes. It's available in a .ZIP'd example download or as a minified CSS style sheet for simple page inclusion.
As you probably already know CSS3 support varies across the various browsers, because of that the buttons will not appear as best as they can in old (or bad) browsers. Listed below is a simple (and hopefully complete) list of support for these CSS3 buttons.
Note: As you can see above there isn't even full support in the latest Internet Explorer, which kind of blows so it's assume it's going to look like ass in older IE browsers.