/*CSS */
b.rtop, b.rbottom{display:block;background:#fff;overflow:hidden;}
b.rtop b, b.rbottom b{display:block;height:1px;
    overflow: hidden; background: #666}
b.r1{margin: 0 5px}
b.r2{margin: 0 3px}
b.r3{margin: 0 2px}
b.rtop b.r4, b.rbottom b.r4{margin: 0 1px;height: 2px}
 
<!-- Markup -->
<div id="wrapper">
<!-- top corners -->
<b class="rtop"><b class="r1"></b><b class="r2"></b><b class="r3"></b><b class="r4"></b></b>
<!-- Content -->
<b class="rbottom"><b class="r4"></b> <b class="r3"></b> <b class="r2"></b> <b class="r1"></b></b>
<!-- bottom content -->
</div>

Requires markup, yes. Cross-Browser compatible, yes. Requires images, no.

BETTER CSS ROUNDED CORNERS

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CSS