Draw a circle (at mouse position), and update radius over time. CSS Houdini Paint API at its best

Code mostly from https://github.com/GoogleChromeLabs/houdini-samples

.ripple {
  --gradient: linear-gradient(to bottom right, deeppink, orangered);
  background: var(--gradient);
}
.ripple.animating {
  background: paint(ripple), var(--gradient);
}