<div class="banner alertPulse-css">
  alertPulse-css
</div>
.alertPulse-css {
    animation: alertPulse 2s ease-out;
    animation-iteration-count: infinite;
    opacity: 1;
    background: #9A2727; /* you need this to specify a color to pulse to */
}

.banner {
  font-family: system-ui;
  margin: 1rem;
  border-radius: 100px;
  font-size: 2.2rem;
  color: white;
  text-align: center;
  padding: 1rem 3rem;
}
body {
  padding: 1rem;
  background: #222222;
}

External CSS

  1. https://s3-us-west-2.amazonaws.com/s.cdpn.io/3/infinite.css

External JavaScript

This Pen doesn't use any external JavaScript resources.