tabler/scss/ui/_progress.scss

@keyframes progress-indeterminate {
  0% {
    right: 100%;
    left: -35%;
  }

  100%,
  60% {
    right: -90%;
    left: 100%;
  }
}

.progress {
  position: relative;
  width: 100%;
  line-height: $progress-height;
  appearance: none;

  &::-webkit-progress-bar {
    background: $gray-100;
  }

  &::-webkit-progress-value {
    background-color: $primary;
  }

  &::-moz-progress-bar {
    background-color: $primary;
  }

  &::-ms-fill {
    background-color: $primary;
    border: none;
  }
}

.progress-sm {
  height: .25rem;
}

.progress-bar-indeterminate {
  &::after,
  &::before {
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    content: "";
    background-color: inherit;
    will-change: left, right;
  }

  &::before {
    animation: progress-indeterminate 2.1s cubic-bezier(.65, .815, .735, .395) infinite;
  }
}