<main>
  <h1>Learn web development</h1>
  <div class="course">
    <h2>Learn CSS</h2>

    <details open>
      <summary>Welcome to Learn CSS!</summary>
      <p>An evergreen CSS course and reference to level up your web styling expertise.</p>
      <p><a href="#">Read Article</a></p>
    </details>

    <details>
      <summary>Box Model</summary>
      <p>Everything displayed by CSS is a box. Understanding how the CSS Box Model works is therefore a core foundation of CSS.</p>
      <p><a href="#">Read Article</a></p>
    </details>

    <details>
      <summary>Selectors</summary>
      <p>To apply CSS to an element you need to select it. CSS provides you with a number of different ways to do this, and you can explore them in this module.</p>
      <p><a href="#">Read Article</a></p>
    </details>

    <details>
      <summary>…</summary>
      <p><em>(chapters 4 to 30 of this course have been omitted for demonstation purposes)</em></p>
    </details>
  </div>
</main>

@layer reset {
  *,
  *:after,
  *:before {
    box-sizing: border-box;
  }

  * {
    margin: 0;
    padding: 0;
  }

  ul[class] {
    list-style: none;
  }

  label {
    cursor: pointer;
    max-width: max-content;
    user-select: none;
  }
}

@layer baselayout {
  html {
    margin: auto;
    line-height: 1.5;
    font-size: 1.25em;
    font-family: "Syne", sans-serif;
    min-height: 100%;
    background: white;
  }

  body {
    width: 100%;
    max-width: 120ch;
    margin: 0 auto;
    min-height: 100dvh;
    padding: 2em;
  }

  footer {
    text-align: center;
    font-style: italic;
    margin-top: 2rem;
  }

  h1,
  h2,
  summary {
    font-family: "Anybody", sans-serif;

    text-decoration: underline;
    text-decoration-color: hsl(156deg 100% 50% / 50%);
    text-decoration-thickness: 0.2rem;
    text-decoration-style: wavy;
    text-decoration-skip-ink: none;
  }

  h2 {
    margin: 2em 0 0.5em 0;
    text-wrap: balance;
  }

  a {
    color: inherit;
  }
}

@layer components {
  @layer course {
    .course {
      counter-reset: chapter;
    }

    .course details {
      counter-increment: chapter;
    }

    .course summary::before {
      content: counter(chapter);
      background: var(--border-color);
      color: white;
      display: inline-block;
      height: 1lh;
      aspect-ratio: 1;
      text-align: center;
      border-radius: 50%;
      margin-right: 0.5em;
    }

    .course details a {
      display: inline-block;
      background: var(--border-color);
      color: white;
      text-decoration: none;
      padding: 0.5em 0.7em;
      font-size: 0.8em;
      text-transform: uppercase;
      background-color: var(--border-color);

      &:hover {
        background-color: lch(from var(--border-color) calc(l * 0.9) c h);
      }
    }
  }
  @layer accordion {
    details {
      --border-color: #6300ff;
      border: 0.25em solid var(--border-color);
      overflow: hidden;
      margin: 0;

      > summary {
        background: #ccc;
        padding: 0.5em;
        border-bottom: 0.25em solid var(--border-color);
        cursor: pointer;

        transition: background 0.25s ease, color 0.25s ease;

        &:hover {
          background: #b4b4b4;
        }
      }

      &[open] {
        border-bottom: 0.25em solid var(--border-color);

        > summary {
          background: #b4b4b4;
        }
      }

      > *:not(summary) {
        padding: 1em;
      }
    }

    /* Visually group successive siblings together */
    details:has(+ details) {
      border-bottom: none;
    }
    details + details {
      border-top: none;
    }
    :not(details) + details,
    details:first-child {
      border-top-left-radius: 0.5em;
      border-top-right-radius: 0.5em;
    }
    details:not(details:has(+ details)) {
      border-bottom-left-radius: 0.5em;
      border-bottom-right-radius: 0.5em;

      &:not([open]) summary {
        border-bottom: 0;
      }
    }
  }
}

@layer utilities {
  .float-right {
    float: right;
    margin-left: 0.5em;
  }
  .float-left {
    float: left;
    margin-right: 0.5em;
  }
  *:has(> .float-right, > .float-left) {
    display: flow-root;
  }

  .sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border-width: 0;
  }
}