brk/website_next/learn/contents/style.css

main.learn {
  > nav {
    --nav-offset: calc(var(--offset) + 2rem);

    counter-reset: content-theme;
    position: sticky;
    top: 0;
    padding-block: var(--nav-offset) var(--offset);
    max-height: 100dvh;
    overflow: auto;
    scrollbar-width: thin;
    font-size: var(--font-size-xs);
    line-height: var(--line-height-xs);
    text-transform: uppercase;
    padding-left: 0.5rem;
    margin-left: -0.5rem;

    ol {
      list-style: none;
      margin: 0;
      padding: 0;
    }

    > ol > li {
      counter-increment: content-theme;
      counter-reset: content-topic;
    }

    > ol > li > ol > li {
      counter-increment: content-topic;
      counter-reset: content-detail;
    }

    > ol > li > ol > li > ol > li {
      counter-increment: content-detail;
    }

    ol ol {
      margin-top: 0.25rem;
      margin-left: 1rem;
      color: var(--gray);
    }

    li + li {
      margin-top: 0.25rem;
    }

    a {
      display: block;
      scroll-margin-block: var(--offset);
      color: inherit;
      text-decoration: none;
      margin-right: 1rem;
      margin-block: -0.25rem;
      margin-left: -0.5rem;
      padding: 0.25rem;
      padding-left: 0.5rem;

      &::before {
        opacity: 0.5;
      }

      &:is(:hover, :active) {
        border-radius: 0.25rem;
      }

      &:hover {
        color: var(--white);
        background-color: var(--dark-gray);
      }

      &[aria-current="location"] {
        color: var(--orange);
      }

      &:active {
        color: var(--black);
        background-color: var(--orange);
      }
    }

    > ol > li > a::before {
      content: counter(content-theme, upper-roman) ". ";
    }

    > ol > li > ol > li > a::before {
      content: counter(content-topic) ". ";
    }

    > ol > li > ol > li > ol > li > a::before {
      content: counter(content-detail, lower-alpha) ". ";
    }
  }
}