.frame
  .center
    - for i in (1..20)
      div class="dot dot-#{i}" style="--index: #{i}"

.frame {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 400px;
  height: 400px;
  margin-top: -200px;
  margin-left: -200px;
  border-radius: 2px;
  box-shadow: 4px 8px 16px 0 rgba(0,0,0,0.1);
  overflow: hidden;
  background: #fff;
  color: #333;
  font-family: 'Open Sans', Helvetica, sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
    background: #4c4ba2;
}

.center {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%,-50%);

}

.center > div {
  --time: calc(60 / calc(40 + 20 - var(--index)) * 1000ms);
  height: 10px;
  width: 10px;
  background:  white;
  margin-bottom: 7px;
  border-radius: 100%;
  animation: dot var(--time) ease-in-out infinite;
}

@keyframes dot {
  0%, 100% {
    transform: translateX(50px);
  }
  50% {
    transform: translateX(-50px);
  }
}