This below content gives you an idea how to make cross-browser compatible rounded corners with CSS.
Example of Rounded Corners:
<!DOCTYPE html>
<html>
<head>
<style>
.roundCorner{
background: #C2C2C2;
border-radius: 25px;
border: 3px solid #C2C2C2;
padding: 15px;
width: 150px;
height: 150px;
}
</style>
</head>
<body>
<div class="roundCorner">Rounded corner div!</div>
</body>
</html>