.center {
    margin: 0;
    position: absolute;
    top: 25%;
    left: 50%;
    margin-right: -50%;
    transform: translate(-50%, -50%)
}

.loader {
  border: 6px solid #f3f3f3; /* Light grey */
  border-top: 6px solid #f44336; /* Blue */
  border-radius: 50%;
  width: 50px;
  height: 50px;
  animation: spin 1s linear infinite;
  position: fixed;
  left: 48%;
  top: 50%;
  transform: translate(-50%, -50%);
}

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