CSS Animated Pulse Buttons using box-shadow

On-trend pulse buttons using CSS animations, @keyframes and box-shadow.
The Examples

See the Pen CSS animated pulse buttons using box shadow by Tipue () on CodePen.

How it works
It make use of CSS animations. First, create a @keyframes sequence. In this case, we're using box-shadow.
CSS
The box-shadow value spread-radius sets the expansion of the shadow effect. Then in the button CSS, invoke the animation property.
CSS
The last value in the animation property is the animation-iteration-count, which is set to infinite in Example 1. In Example 2 it's set to 3 iterations, and in example 3, a single instance.
CSS
CSS animations work with IE11, Microsoft Edge 17+, Chrome 49+, Firefox 61+, Safari 11.1+, iOS Safari 10.3+, Chrome for Android 67+ and Samsung Internet 4+.