<!DOCTYPE html>
<html>
<head>
<meta charset='utf-8'>
<meta http-equiv='X-UA-Compatible' content='IE=edge'>
<title>Rainbow Underline Effect</title>
<meta name='viewport' content='width=device-width, initial-scale=1'>
<link rel='stylesheet' type='text/css' media='screen' href='style.css'>
</head>
<body>
<a href="#">Hover this link</a>
</body>
</html>