wagtail/client/scss/components/_ping.scss

@keyframes ping-warning {
  0% {
    box-shadow: 0 0 0 0
      hsla(
        var(--w-color-warning-100-hue),
        var(--w-color-warning-100-saturation),
        var(--w-color-warning-100-lightness),
        0.7
      );
  }

  25% {
    box-shadow: 0 0 0 10px
      hsla(
        var(--w-color-warning-100-hue),
        var(--w-color-warning-100-saturation),
        var(--w-color-warning-100-lightness),
        0
      );
  }

  50% {
    box-shadow: 0 0 0 0
      hsla(
        var(--w-color-warning-100-hue),
        var(--w-color-warning-100-saturation),
        var(--w-color-warning-100-lightness),
        0
      );
  }
}

@keyframes ping-critical {
  0% {
    box-shadow: 0 0 0 0
      hsla(
        var(--w-color-critical-100-hue),
        var(--w-color-critical-100-saturation),
        var(--w-color-critical-100-lightness),
        0.7
      );
  }

  25% {
    box-shadow: 0 0 0 8px
      hsla(
        var(--w-color-critical-100-hue),
        var(--w-color-critical-100-saturation),
        var(--w-color-critical-100-lightness),
        0
      );
  }

  50% {
    box-shadow: 0 0 0 0
      hsla(
        var(--w-color-critical-100-hue),
        var(--w-color-critical-100-saturation),
        var(--w-color-critical-100-lightness),
        0
      );
  }
}

.w-ping {
  &.w-ping--critical {
    @media (prefers-reduced-motion: no-preference) {
      animation: ping-critical 5s 5;
    }
  }
}