<!DOCTYPE html>
<html>
<body>
<h1>The input required attribute</h1>
<p>The required attribute specifies that an input field must be filled out before submitting the form.</p>
<form action="/action_page.php">
<label for="username">Username:</label>
<input type="text" id="username" name="username" required>
<input type="submit" value="Submit">
</form>
</body>
</html>