<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
<style>
.rescircle {
width: 20%;
border-radius: 50%;
background: #b5b5b5;
}
.rescircle:after {
content: "";
display: block;
padding-bottom: 100%;
}
</style>
</head>
<body>
<div class="rescircle"></div>
</body>
</html>