纯css 圆角实现代码

<div class="curvedBox">
<span>
<span class="r1" ></span>
<span class="r2" ></span>
<span class="r3" ></span>
<span class="r4" ></span>
</span>
<div class="content">
Flex is a cross-platform development framework for creating rich Inter applications (RIAs). Flex enables you to create expressive, high-performance applications that run identically on all major browsers and operating systems.
</div>
<span>
<span class="r4" ></span>
<span class="r3" ></span>
<span class="r2" ></span>
<span class="r1" ></span>
</span>
</div>

body{background-color:#000;}
.curvedBox{width:300px;margin: 2510px auto 0;}
.curvedBox .r1,.curvedBox .r2,.curvedBox .r3,.curvedBox .r4{background-color:#fff;display:block;overflow:hidden;height:1px;font-size:1px;}
.curvedBox .r2,.curvedBox .r3,.curvedBox .r4{border-width:0 1px;border-left:1px solid #fff;border-right:1px solid #fff;}
.curvedBox .r1{margin:0 6px;}
.curvedBox .r2{margin:0 3px;}
.curvedBox .r3{margin:0 2px;}
.curvedBox .r4{margin:0 1px;height:2px;}
.curvedBox .content{background:#fff;border-left:1px solid #fff;border-right:1px solid #fff;padding:0 5px;}