<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=½, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button>Open</button>

    <dialog id="modal">
        <h1>Dialog</h1>
        <p>Dialog content</p>
        <button>Close</button>
    </dialog>

    <script>
        let dialog = document.querySelector('#modal');
        let button = document.querySelector('button');
        let closeButton = dialog.querySelector('button');

        button.addEventListener('click', function() {
            dialog.showModal();
        });
        
        closeButton.addEventListener('click', function() {
            dialog.close();
        });
    </script>
</body>
</html>