1.Make a top navbar using HTML
2.Create a form
Example:
<form action="" method="get" onSubmit="return confirm('Do you wat to close this application?');">
<button name="close">close</button>
</form>
<?php
//here I use a trick to close application using PHP & Javascript
if(isset($_GET['close'])){
echo "<script>"; echo "window.close()"; echo "</script>";
}
?>