I would like the animation to loop steady

[Inneedoflearning]

Hello folks, below is my code and I would like the animation to loop continuously once click

 

<div class="w3-container w3-center">
    <p id="Demo">Animation is Fun!</p>
    <button class="w3-bar-item w3-green " type="button" onclick="myFunction()" class="w3-button">Touch me</button>
</div>
                        <p>The w3-animate-top class slides in an element from the top.</p>

<script>
function myFunction() {
    var x = document.getElementById("Demo");
    if (x.className.indexOf("w3-animate-top") == -1) {
        x.className += " w3-animate-top";
    } else {
        x.className = x.className.animate(" w3-animate-top", "");
    }
}
</script>