SOURCE

<div class="scan">
</div>

.scan {
  width: 150px;
  height: 150px;
  margin: 30px auto;
  position: relative;
  background: linear-gradient(to left, #108EE9, #108EE9) left top no-repeat, linear-gradient(to bottom, #108EE9, #108EE9) left top no-repeat, linear-gradient(to left, #108EE9, #108EE9) right top no-repeat, linear-gradient(to bottom, #108EE9, #108EE9) right top no-repeat, linear-gradient(to left, #108EE9, #108EE9) left bottom no-repeat, linear-gradient(to bottom, #108EE9, #108EE9) left bottom no-repeat, linear-gradient(to left, #108EE9, #108EE9) right bottom no-repeat, linear-gradient(to left, #108EE9, #108EE9) right bottom no-repeat;
  background-size: 3px 20px, 20px 3px, 3px 20px, 20px 3px;
}

.scan::after {
  content: '';
  width: 140px;
  border: 1px solid #BBE2FF;
  position: absolute;
  left: 5px;
  top: 2px;
  animation: myfirst 4s infinite;
}

@keyframes myfirst {
  from {
    top: 2px;
  }
  to {
    top: 144px;
  }
}