【CSS】How to slowly animate multiple circular lines using @keyframes | Demo page

.block {
  position: relative;
  width: 540px;
  height: 540px;
  margin: 70px auto 0;
}

.block p {
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  z-index: 2;
}

.block p:before {
  display: block;
  content: '';
  position: absolute;
  left: -1.5%;
  top: -1.5%;
  width: 103%;
  height: 103%;
  border: 1px solid #2388ff;
  border-radius: 50%;
  opacity: .75;
}

.border1 {
  transform-origin: 50.5% 49.5%;
  animation: round 3.7s linear infinite;
}

.border2 {
  transform-origin: 49.5% 50.2%;
  animation: round 4.8s linear infinite .1s;
}

.border3 {
  transform-origin: 50.8% 49.7%;
  animation: round 3.5s linear infinite;
}

@keyframes round {
  100% {
  transform: rotate(360deg);
  }
}

@media screen and (max-width:640px){
  .block {
    width: 300px;
    height: 300px;
  }
}