How can the code be improved to adhere to modern HTML standards?

The code can be improved to adhere to modern HTML standards by replacing the outdated HTML attributes like align, bgcolor, and border with CSS properties. This will make the code more semantic, accessible, and easier to maintain.

<?php
echo '<div style="text-align: center; background-color: #f0f0f0; padding: 10px;">';
echo '<h1>Welcome to our website!</h1>';
echo '<p>This is a paragraph of text.</p>';
echo '</div>';
?>