<!DOCTYPE html>
<html>
<head>
<style type='text/css'>
.round {
background: radial-gradient(circle at 0 100%, rgba(11, 111, 111, 0) 14px,#c00 15px),
radial-gradient(circle at 100% 100%, rgba(111, 0, 0, 0) 14px, #c00 15px),
radial-gradient(circle at 100% 0, rgba(1, 111, 0, 0) 14px, #c00 15px),
radial-gradient(circle at 0 0, rgba(204, 111, 0, 0) 14px, #c00 15px);
background-position: bottom left, bottom right, top right, top left;
background-size: 50% 50%;
background-repeat: no-repeat;
padding: 14px;
}
</style>
</head>
<body>
<div class="round">w3cschool.cn</div>
</body>
</html>