spin.js/spin.css

A spinning activity indicator

@keyframes spinner-line-fade-more {
  0%, 100% {
    opacity: 0; /* minimum opacity */
  }
  1% {
    opacity: 1;
  }
}

@keyframes spinner-line-fade-quick {
  0%, 39%, 100% {
    opacity: 0.25; /* minimum opacity */
  }
  40% {
    opacity: 1;
  }
}

@keyframes spinner-line-fade-default {
  0%, 100% {
    opacity: 0.22; /* minimum opacity */
  }
  1% {
    opacity: 1;
  }
}

@keyframes spinner-line-shrink {
  0%, 25%, 100% {
    /* minimum scale and opacity */
    transform: scale(0.5);
    opacity: 0.25;
  }
  26% {
    transform: scale(1);
    opacity: 1;
  }
}