wagtail/client/scss/components/_loading-mask.scss

@use 'sass:map';
// Loading mask: overlays a certain area with a loading spinner and a faded out cover to prevent interaction
.loading-mask {
  &.loading {
    position: relative;

    &:before,
    &:after {
      position: absolute;
      display: block;
    }

    &:before {
      content: '';
      top: -5px;
      inset-inline-start: -5px;
      bottom: -5px;
      inset-inline-end: -5px;
      z-index: 1;
      background-color: theme('colors.white-50');
    }

    &:after {
      content: '';
      display: block;
      width: 1.875rem;
      height: 1.875rem;
      inset-inline-start: 50%;
      top: 50%;
      animation: spin-wag 0.5s infinite linear;
      mask-image: url('#{$images-root}icons/spinner.svg');
      mask-repeat: no-repeat;
      z-index: 2;
      background: theme('colors.surface-button-default');
    }
  }
}