<!DOCTYPE html>
<html>
<head>
<style>
input:default { box-shadow: 0 0 1px 1px red;
}
</style>
</head>
<body>
<h1>The default Selector</h1>
<p>The :default selector selects the default form element in a group of related elements.</p>
<p>The "male" radio button is checked by default:</p>
<form action="">
<input type="radio" name="gender" value="male" checked> Male<br>
<input type="radio" name="gender" value="female"> Female<br>
<input type="radio" name="gender" value="other"> Other
</form>
<p>The :default selector is not supported in Internet Explorer 11 and earlier versions.</p>
</body>
</html>