HTML的DOM结构如下，用一个div层做容器，另外再用四个层，分别用来容纳四个圆角。

<div id="RdDemo" class="container">
  <div class="corner lt"></div>
  <div class="corner rt"></div>
  <div class="corner lb"></div>
  <div class="corner rb"></div>
</div>

然后我用Paint.NET换一个院直径20px,不会用PS只能用这么傻瓜式的工具，然后导入Expression Design切分成四个半圆，导出效果如下

对容器container定义如下样式

.container{
    position:relative;
    padding:10px;
    width:360px;
    margin:20px;
}

.corner{
    position:absolute;
    height:10px;
    width:10px;
}
.lt{
    left:0px;
    top:0px;
    background-image:url('img/lt.gif');
}
.rt{
       right:0px;
       top:0px;
       background-image:url('img/rt.gif');
}
.lb{
    left:0px;
    bottom:0px;
        background-image:url('img/lb.gif');
}
.rb{
    right:0px;
    bottom:0px;
    background-image:url('img/rb.gif');
}

<div id="RdDemo" class="container">
  <strong>Hello round corner</strong>
  <p>OK,let's get started</p>
  <p>I always needed time on my own<br />
     I never thought I'd need you there when I cry<br />
     And the days feel like years when I'm alone<br />
     And the bed where you lie<br />
     is made up on your side<br />
  </p>
  <div class="corner lt"></div>
  <div class="corner rt"></div>
  <div class="corner lb"></div>
  <div class="corner rb"></div>
</div>

• css
• 圆角