wagtail/client/scss/components/_drilldown.scss

.w-drilldown__contents {
  max-height: min(480px, 70vh);
  overflow-y: auto;
}

.w-drilldown .w-drilldown__toggle {
  @apply w-label-1;
  display: flex;
  justify-content: space-between;
  padding-inline-start: theme('spacing.5');
  padding-inline-end: theme('spacing.5');
  border: 1px solid transparent;

  &:hover {
    background-color: transparent;
    border-color: theme('colors.border-button-outline-hover');
    color: theme('colors.text-link-hover');
    cursor: pointer;

    @media (forced-colors: active) {
      border-color: Highlight;
    }
  }

  .icon {
    pointer-events: none;
    width: theme('spacing.5');
    height: theme('spacing.5');
    margin-inline-end: 0;
  }
}

.w-drilldown__submenu {
  display: grid;
  grid-template-columns: min-content 1fr;
  padding-inline-end: theme('spacing.4');
}

.w-drilldown .w-drilldown__back {
  @apply w-label-1;
  position: relative;
  padding: theme('spacing.[2.5]');
  align-self: flex-start;

  .icon {
    pointer-events: none;
    margin-inline-end: 0;
  }

  &:hover {
    background-color: transparent;
    border-color: theme('colors.border-button-outline-hover');
    color: theme('colors.text-link-hover');
    cursor: pointer;

    @media (forced-colors: active) {
      border-color: Highlight;
    }
  }
}

.w-drilldown__submenu .w-field__wrapper {
  // Align the margin-top with the submenu’s back button
  // and reduce the default margin-bottom.
  margin-top: theme('spacing.2');
  margin-bottom: theme('spacing.2');
  // Force fields to stay within the width of the drilldown.
  max-width: calc(260px - theme('spacing.4'));
}

.w-drilldown__submenu .w-field__label {
  @apply w-label-1;
  margin-bottom: theme('spacing.3');
}

.w-drilldown__count {
  $badge-size: theme('spacing.4');
  width: $badge-size;
  height: $badge-size;
  line-height: 1.5;
  text-align: center;
  font-size: 0.5625rem;
  font-weight: theme('fontWeight.bold');
  border-radius: theme('borderRadius.full');
  background-color: theme('colors.info.100');
  border: 1px solid theme('colors.info.100');
  color: theme('colors.white.DEFAULT');

  // Reuse the same count component as a button badge.
  .w-filter-button & {
    position: absolute;
    top: calc(-0.5 * #{$badge-size});
    inset-inline-end: calc(-0.5 * #{$badge-size});
  }
}