By using CSS3 property border-radius we can make the control border curve or circle, the below example will let you know how to do that.
Source Code:
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<div style="border-radius: 25px;height: 200px;width: 200px;margin: 10px;background: green;float:left;">
</div>
<div style="border-radius: 100px;height: 200px;width: 200px;margin: 10px;background: orange;float:left;">
</div>
</div>
</form>
</body>
</html>
Output:
