<button>Find out more</button>

body {
  height: 100vh;
  margin: 0;
  display: grid;
  place-items: center;
}

@import url('https://fonts.googleapis.com/css2?family=Roboto&display=swap');

button {
  position: relative;
  overflow: hidden;
  transition: background 400ms;
  color: #fff;
  background-color: #6200ee;
  padding: 1rem 2rem;
  font-family: 'Roboto', sans-serif;
  font-size: 1.5rem;
  outline: 0;
  border: 0;
  border-radius: 0.25rem;
  box-shadow: 0 0 0.5rem rgba(0, 0, 0, 0.3); /* black with 30% opacity */
  cursor: pointer;
}

span.ripple {
  position: absolute;
  border-radius: 50%;
  transform: scale(0);
  animation: ripple 600ms linear;
  background-color: rgba(255, 255, 255, 0.7);
}

@keyframes ripple {
  to {
    transform: scale(4);
    opacity: 0;
  }
}

function createRipple(event) {
  const button = event.currentTarget;

  const circle = document.createElement("span");
  const diameter = Math.max(button.clientWidth, button.clientHeight);
  const radius = diameter / 2;

  circle.style.width = circle.style.height = `${diameter}px`;
  circle.style.left = `${event.clientX - button.offsetLeft - radius}px`;
  circle.style.top = `${event.clientY - button.offsetTop - radius}px`;
  circle.classList.add("ripple");

  const ripple = button.getElementsByClassName("ripple")[0];

  if (ripple) {
    ripple.remove();
  }

  button.appendChild(circle);
}

const buttons = document.getElementsByTagName("button");
for (const button of buttons) {
  button.addEventListener("click", createRipple);
}