angular/adev/shared-docs/styles/_faceted-list.scss

@mixin faceted-list() {
  .docs-faceted-list {
    --faceted-list-border-width: 2px;
    list-style: none;
    padding: 0;
    margin: 0;
    border-inline-start: calc(var(--faceted-list-border-width) - 1px) solid var(--senary-contrast);
  }
  .docs-faceted-list-item {
    a,
    button:not(.docs-expanded-button) {
      position: relative;
      background-color: var(--quaternary-contrast);
      background-clip: text;
      -webkit-background-clip: text;
      color: transparent;
      transition: background-color 0.3s ease;

      &::before {
        content: '';
        position: absolute;
        top: 0;
        left: calc(var(--faceted-list-border-width) * -1);
        width: var(--faceted-list-border-width);
        height: 100%;
        background: var(--primary-contrast);
        opacity: 0;
        transform: scaleY(0.7);
        transition: transform 0.3s ease, opacity 0.3s ease;
      }

      &:hover {
        background-color: var(--primary-contrast);
        &::before {
          opacity: 0.3;
        }
      }

      &.docs-faceted-list-item-active {
        // font gradient
        background-image: var(--pink-to-purple-vertical-gradient);

        &::before {
          opacity: 1;
          transform: scaleY(1);
          background: var(--pink-to-purple-vertical-gradient);
        }

        &:hover {
          &::before {
            opacity: 1;
            transform: scaleY(1.1);
          }
        }
      }
    }
  }
}