<div class="wrap">
  <div class="loader"></div>
</div>

body {
  background-color: #22303d;
}

.wrap {
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
  margin: auto;
  width: 150px;
  height: 150px;
  background-color: #22303d;
  border-radius: 75px;
  overflow: hidden;
  box-shadow: 0px 3px 3px rgba(0,0,0,.4);
}

@keyframes "borders" {
  0% {
    border-top-color: #4f6f8f;
    border-left-color: #46637f;
    border-bottom-color: #3d566e;
    border-right-color: #34495e;
  }

  20% {
    border-left-color: #4f6f8f;
    border-bottom-color: #46637f;
    border-right-color: #3d566e;
    border-top-color: #34495e;
  }

  40% {
    border-bottom-color: #4f6f8f;
    border-right-color: #46637f;
    border-top-color: #3d566e;
    border-left-color: #34495e;
  }

  80% {
    border-right-color: #4f6f8f;
    border-top-color: #46637f;
    border-left-color: #3d566e;
    border-bottom-color: #34495e;
  }

  100% {
    border-top-color: #4f6f8f;
    border-left-color: #46637f;
    border-bottom-color: #3d566e;
    border-right-color: #34495e;
  }
}

.loader {
  box-sizing: border-box;
  width: 150px;
  height: 150px;
  border-width: 75px;
  border-style: solid;
  animation: borders 1s linear infinite;
}