.center {
    margin: 0;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-right: -50%;
    transform: translate(-50%, -50%)
    font-size: 24px;
    font-family: sans-serif;
}

.dot {
  opacity: 0;
  animation: blink 1.5s infinite;
}

.dot:nth-child(2) {
  animation-delay: 0.3s;
}

.dot:nth-child(3) {
  animation-delay: 0.6s;
}

.dot:nth-child(4) {
  animation-delay: 0.9s;
}

@keyframes blink {
  0%, 100% { opacity: 0; }
  20% { opacity: 1; }
}