CSS :optional Pseudo Class - Playground Example

<!DOCTYPE html>
<html>
<head>
<style type="text/css">
input:optional { 
   border:1px dashed green; 
} 
</style>
</head>
<body>
<p>Please enter your name and age.</p> 
<p>Name: <input name="name" required ></p> 
<p>Age: <input type="number" name="old"> (Optional)</p> 
<p><button>Submit</button></p>
</body>
</html>