wagtail/client/scss/components/_dismissible.scss

@keyframes pulse-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
      );
  }
}

.w-dismissible-badge {
  border-radius: theme('borderRadius.full');
  background-color: theme('colors.warning.100');
  flex-shrink: 0;
  min-width: theme('spacing.[2.5]');
  height: theme('spacing.[2.5]');

  @media (forced-colors: active) {
    border: 3px solid transparent;
    box-sizing: content-box;
  }

  &--count {
    color: theme('colors.surface-menus');
    text-align: center;
    font-size: 0.625rem;
    font-weight: theme('fontWeight.bold');
    min-width: theme('spacing.[3.5]');
    height: theme('spacing.[3.5]');
    line-height: theme('lineHeight.tight');

    @media (prefers-reduced-motion: no-preference) {
      animation: pulse-warning 5s 5;
    }
  }
}