32 CSS Accordions — Vertical & Horizontal04 / 32

Pure CSSMIT licensed

Nested Multi-Level Accordion (CSS Tree View for Docs & File Explorers)

Three levels of <details> nested like a file explorer: folder chevrons, connector tree-lines drawn with borders, per-level indentation and file-type dots — the recursive structure devs need for documentation sidebars, org charts and directory browsers, with hierarchy you can read at a glance.

Published

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The code

<section class="acc-04" aria-label="Nested multi-level accordion tree demo">
  <div class="acc-04__panel">
    <p class="acc-04__crumb">docs / <b>design-system</b></p>
    <details class="acc-04__branch" open>
      <summary class="acc-04__folder">Foundations</summary>
      <div class="acc-04__kids">
        <details class="acc-04__branch" open>
          <summary class="acc-04__folder">Color</summary>
          <div class="acc-04__kids">
            <a href="#" class="acc-04__leaf" style="--dot:#5b8def">palette.md</a>
            <a href="#" class="acc-04__leaf" style="--dot:#5b8def">semantic-tokens.md</a>
            <a href="#" class="acc-04__leaf" style="--dot:#e0a63c">contrast-audit.xlsx</a>
          </div>
        </details>
        <details class="acc-04__branch">
          <summary class="acc-04__folder">Typography</summary>
          <div class="acc-04__kids">
            <a href="#" class="acc-04__leaf" style="--dot:#5b8def">type-scale.md</a>
            <a href="#" class="acc-04__leaf" style="--dot:#c95ddb">specimens.fig</a>
          </div>
        </details>
        <a href="#" class="acc-04__leaf" style="--dot:#5b8def">spacing.md</a>
      </div>
    </details>
    <details class="acc-04__branch">
      <summary class="acc-04__folder">Components</summary>
      <div class="acc-04__kids">
        <details class="acc-04__branch">
          <summary class="acc-04__folder">Forms</summary>
          <div class="acc-04__kids">
            <a href="#" class="acc-04__leaf" style="--dot:#5b8def">inputs.md</a>
            <a href="#" class="acc-04__leaf" style="--dot:#5b8def">validation.md</a>
          </div>
        </details>
        <a href="#" class="acc-04__leaf" style="--dot:#5b8def">accordion.md</a>
        <a href="#" class="acc-04__leaf" style="--dot:#5b8def">navigation.md</a>
      </div>
    </details>
    <details class="acc-04__branch">
      <summary class="acc-04__folder">Release notes</summary>
      <div class="acc-04__kids">
        <a href="#" class="acc-04__leaf" style="--dot:#54b06d">v3.2.0.md</a>
        <a href="#" class="acc-04__leaf" style="--dot:#54b06d">v3.1.4.md</a>
      </div>
    </details>
  </div>
</section>
.acc-04,
.acc-04 *,
.acc-04 *::before,
.acc-04 *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

.acc-04 {
  --accent: oklch(0.55 0.15 265);
  --line: #dcdfeb;
  --indent: 22px;
  font-family: 'Segoe UI',system-ui,sans-serif;
  width: 100%;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #eef0f6;
  padding: 40px 20px;
}

.acc-04__panel {
  width: min(380px,100%);
  background: #fff;
  border-radius: 16px;
  padding: 22px 20px 26px;
  box-shadow: 0 24px 60px -34px rgba(30,35,80,.35);
}

.acc-04__crumb {
  font-family: ui-monospace,Menlo,monospace;
  font-size: 12px;
  color: #8a90a8;
  margin-bottom: 12px;
}

.acc-04__crumb b {
  color: #2a3050;
}

.acc-04__folder {
  list-style: none;
  display: flex;
  align-items: center;
  gap: 9px;
  min-height: 40px;
  padding: 0 8px;
  font-size: 14.5px;
  font-weight: 600;
  color: #2a3050;
  cursor: pointer;
  border-radius: 8px;
  transition: background .15s;
}

.acc-04__folder::-webkit-details-marker {
  display: none;
}

.acc-04__folder::marker {
  content: "";
}

.acc-04__folder:hover {
  background: #f3f5fa;
}

.acc-04__folder::before {
  content: "";
  width: 7px;
  height: 7px;
  border-right: 2px solid #9aa1bd;
  border-bottom: 2px solid #9aa1bd;
  transform: rotate(-45deg);
  transition: transform .2s;
  flex: none;
  margin-left: 2px;
}

.acc-04__branch[open] > .acc-04__folder::before {
  transform: rotate(45deg);
}

.acc-04__branch[open] > .acc-04__folder {
  font-weight: 750;
  color: var(--accent);
}

.acc-04__kids {
  margin-left: var(--indent);
  border-left: 1.5px solid var(--line);
  padding-left: 6px;
  display: flex;
  flex-direction: column;
}

.acc-04__leaf {
  display: flex;
  align-items: center;
  gap: 9px;
  min-height: 38px;
  padding: 0 8px;
  font-size: 13.5px;
  color: #4b5270;
  text-decoration: none;
  border-radius: 8px;
  transition: background .15s;
}

.acc-04__leaf:hover {
  background: #f3f5fa;
  color: var(--accent);
}

.acc-04__leaf::before {
  content: "";
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--dot,#9aa1bd);
  flex: none;
  margin-left: 1px;
}

.acc-04__folder:focus-visible,
.acc-04__leaf:focus-visible {
  outline: 3px solid var(--accent);
  outline-offset: 1px;
}

@media (prefers-reduced-motion: reduce) {
  .acc-04__folder::before {
    transition: none;
  }
}
/* No JavaScript — details elements nest recursively; indentation + border-left connector lines make depth legible, and the same classes work at every level. */
Paste this into ChatGPT, Claude, Cursor, or any coding assistant. The block below is pre-framed with everything the AI needs to integrate this demo into your project — markup, styles, scoping notes, and the source URL. Hit Copy and paste straight into your chat.
Here's a working CSS Accordions — Vertical & Horizontal from CodeFronts. Use it as-is or adapt to your framework. All classes are scoped under a unique prefix so the code won't collide with your existing styles. MIT licensed.
Demo: Nested Multi-Level Accordion (CSS Tree View for Docs & File Explorers)
Source: https://codefronts.com/navigation/css-accordions/nested-multi-level-accordion-tree-view/

Three levels of <details> nested like a file explorer: folder chevrons, connector tree-lines drawn with borders, per-level indentation and file-type dots — the recursive structure devs need for documentation sidebars, org charts and directory browsers, with hierarchy you can read at a glance.
## HTML
```html
<section class="acc-04" aria-label="Nested multi-level accordion tree demo">
  <div class="acc-04__panel">
    <p class="acc-04__crumb">docs / <b>design-system</b></p>
    <details class="acc-04__branch" open>
      <summary class="acc-04__folder">Foundations</summary>
      <div class="acc-04__kids">
        <details class="acc-04__branch" open>
          <summary class="acc-04__folder">Color</summary>
          <div class="acc-04__kids">
            <a href="#" class="acc-04__leaf" style="--dot:#5b8def">palette.md</a>
            <a href="#" class="acc-04__leaf" style="--dot:#5b8def">semantic-tokens.md</a>
            <a href="#" class="acc-04__leaf" style="--dot:#e0a63c">contrast-audit.xlsx</a>
          </div>
        </details>
        <details class="acc-04__branch">
          <summary class="acc-04__folder">Typography</summary>
          <div class="acc-04__kids">
            <a href="#" class="acc-04__leaf" style="--dot:#5b8def">type-scale.md</a>
            <a href="#" class="acc-04__leaf" style="--dot:#c95ddb">specimens.fig</a>
          </div>
        </details>
        <a href="#" class="acc-04__leaf" style="--dot:#5b8def">spacing.md</a>
      </div>
    </details>
    <details class="acc-04__branch">
      <summary class="acc-04__folder">Components</summary>
      <div class="acc-04__kids">
        <details class="acc-04__branch">
          <summary class="acc-04__folder">Forms</summary>
          <div class="acc-04__kids">
            <a href="#" class="acc-04__leaf" style="--dot:#5b8def">inputs.md</a>
            <a href="#" class="acc-04__leaf" style="--dot:#5b8def">validation.md</a>
          </div>
        </details>
        <a href="#" class="acc-04__leaf" style="--dot:#5b8def">accordion.md</a>
        <a href="#" class="acc-04__leaf" style="--dot:#5b8def">navigation.md</a>
      </div>
    </details>
    <details class="acc-04__branch">
      <summary class="acc-04__folder">Release notes</summary>
      <div class="acc-04__kids">
        <a href="#" class="acc-04__leaf" style="--dot:#54b06d">v3.2.0.md</a>
        <a href="#" class="acc-04__leaf" style="--dot:#54b06d">v3.1.4.md</a>
      </div>
    </details>
  </div>
</section>
```
## CSS
```css
.acc-04,
.acc-04 *,
.acc-04 *::before,
.acc-04 *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

.acc-04 {
  --accent: oklch(0.55 0.15 265);
  --line: #dcdfeb;
  --indent: 22px;
  font-family: 'Segoe UI',system-ui,sans-serif;
  width: 100%;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #eef0f6;
  padding: 40px 20px;
}

.acc-04__panel {
  width: min(380px,100%);
  background: #fff;
  border-radius: 16px;
  padding: 22px 20px 26px;
  box-shadow: 0 24px 60px -34px rgba(30,35,80,.35);
}

.acc-04__crumb {
  font-family: ui-monospace,Menlo,monospace;
  font-size: 12px;
  color: #8a90a8;
  margin-bottom: 12px;
}

.acc-04__crumb b {
  color: #2a3050;
}

.acc-04__folder {
  list-style: none;
  display: flex;
  align-items: center;
  gap: 9px;
  min-height: 40px;
  padding: 0 8px;
  font-size: 14.5px;
  font-weight: 600;
  color: #2a3050;
  cursor: pointer;
  border-radius: 8px;
  transition: background .15s;
}

.acc-04__folder::-webkit-details-marker {
  display: none;
}

.acc-04__folder::marker {
  content: "";
}

.acc-04__folder:hover {
  background: #f3f5fa;
}

.acc-04__folder::before {
  content: "";
  width: 7px;
  height: 7px;
  border-right: 2px solid #9aa1bd;
  border-bottom: 2px solid #9aa1bd;
  transform: rotate(-45deg);
  transition: transform .2s;
  flex: none;
  margin-left: 2px;
}

.acc-04__branch[open] > .acc-04__folder::before {
  transform: rotate(45deg);
}

.acc-04__branch[open] > .acc-04__folder {
  font-weight: 750;
  color: var(--accent);
}

.acc-04__kids {
  margin-left: var(--indent);
  border-left: 1.5px solid var(--line);
  padding-left: 6px;
  display: flex;
  flex-direction: column;
}

.acc-04__leaf {
  display: flex;
  align-items: center;
  gap: 9px;
  min-height: 38px;
  padding: 0 8px;
  font-size: 13.5px;
  color: #4b5270;
  text-decoration: none;
  border-radius: 8px;
  transition: background .15s;
}

.acc-04__leaf:hover {
  background: #f3f5fa;
  color: var(--accent);
}

.acc-04__leaf::before {
  content: "";
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--dot,#9aa1bd);
  flex: none;
  margin-left: 1px;
}

.acc-04__folder:focus-visible,
.acc-04__leaf:focus-visible {
  outline: 3px solid var(--accent);
  outline-offset: 1px;
}

@media (prefers-reduced-motion: reduce) {
  .acc-04__folder::before {
    transition: none;
  }
}
```

## JavaScript
```js
/* No JavaScript — details elements nest recursively; indentation + border-left connector lines make depth legible, and the same classes work at every level. */
```

How this works

Nesting <details> inside <details> just works — each level toggles independently and keyboard flow follows document order. The design work is making depth legible: every child list gets margin-left plus a border-left connector line, so the eye traces parent→child like a tree diagram, and each nesting level re-uses the same classes — the structure is genuinely recursive, so templating loops render it directly.

Leaf rows (files) are plain links with a colored dot keyed by type via --dot; branch rows (folders) are summaries with a caret that rotates 90° when open — the same affordance at every depth keeps the mental model consistent. A subtle [open] font-weight bump marks which branches along your path are expanded.

Techniques used: recursive details-in-details nesting (no depth-specific CSS) · border-left connector lines + margin-left indentation rhythm · caret rotate(90deg) folder affordance · type-coded leaf dots via per-item --dot custom property · consistent 40px rows at every level for scan rhythm

Make it yours

  • Indent width and line color = --indent / --line tokens.
  • Add levels freely — the classes are depth-agnostic; recursion is free.
  • Leaf dot colors are per-item --dot inline variables.
  • Pre-expand a path by adding open down the chain.

Gotchas — read before shipping

  • Cap real-world nesting at 3 levels — beyond that users lose track of where they are; flatten the taxonomy or add a breadcrumb instead.
  • Connector lines are decorative: hierarchy must ALSO be conveyed by the DOM nesting itself (it is — details-in-details), never by indentation alone.
  • Don't make the whole row a link AND a toggle — here folders toggle, files navigate, and the two are visually distinct (caret vs dot).
  • For huge trees (100+ nodes), details is still fine for rendering, but consider content-visibility:auto on deep branches to keep first paint fast.

Browser support

ChromeSafariFirefoxEdge
111+15.4+113+111+

Floor set by oklch() as this demo is written. The core technique itself goes back further — Chrome all.

Nested details/summary is universally supported — it's just HTML. Everything else is borders, transforms and custom properties.

Techniques used in this demo

oklch()MDN ↗

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