.center {
    margin: 0;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-right: -50%;
    transform: translate(-50%, -50%)
}
.loader {
  border: 4px solid #607D8B;
  border-radius: 50%;
  border-top: 4px solid #0f493f;
  width: 36px;
  height: 36px;
  margin-top: 28px;
  margin-left: 78px;
  position: absolute;
  -webkit-animation: spin 1s linear infinite; /* Safari */
  animation: spin 1s linear infinite;
}

/* Safari */
@-webkit-keyframes spin {
  0% { -webkit-transform: rotate(0deg); }
  100% { -webkit-transform: rotate(360deg); }
}

@keyframes spin {
  0% { transform: rotate(0deg); }
  100% { transform: rotate(360deg); }
}