CSS animations

https://jsfiddle.net/v0vh2jug/
http://danielcwilson.com/blog/2015/07/animations-part-1/

<script src="web-animations.min.js"></script>
<div class="pulse" style="width: 150px;">Hello world!</div>
<script>
    var elem = document.querySelector('.pulse');
    var animation = elem.animate({
        opacity: [0.5, 1],
        transform: ['scale(0.5)', 'scale(1)'],
    }, {
        direction: 'alternate',
        duration: 500,
        iterations: Infinity,
    });
</script>