Clip borders/ rounded corner of webpage like twitter?

I want to build a webpage like twitter or microsoft hohm. Like clipping borders, buttons, clipped text box. How can I do this in Dreamweaver? Is these things are done b开发者_运维百科y photoshop? Any tutorial or links will be very helpful. If there are any webdesign template of twitter of something like twitter please let me know.

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Its done by CSS.

<div id="wrapper">
...
</div>

<style type="text/css">
#wrapper{
      width:800px;
      margin:0 auto;
}
</style>