body {
  font-size: 16px;
  font-family: Helvetica;
  line-height: 1.5;
  
  background-color: #000000;
  color: #ffffff;
}

h1 {
  position: absolute;
  top: 50%;
  left: 50%;
  font-size: 20vmin;
  transform: translate(-50%, -50%);
}

@keyframes heartbeat {
  0% { transform: translate(-50%, -50%) scale(1); }
  50% { transform: translate(-50%, -50%) scale(1.1); }
  100% { transform: translate(-50%, -50%) scale(1); }
}

div.ball {
  background-color: #ffffff;
  width: 200px;
  height: 200px;
  border-radius: 50%;
  
  position: absolute;
  top: 0;
  left: 0;
  transform: translate(-50%, -50%);
  
  mix-blend-mode: difference;
  animation: heartbeat 5s infinite;
}