Edit in JSFiddle

Result
HTML
CSS

<div>角丸</div>

div{
with: 300px;
height: 250px;
color: #fff;
background: #000;
text-align: center;
line-height: 250px;
-webkit-border-radius: 20px;
-moz-border-radius: 20px;
border-radius: 20px;
}