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Added 30 Aug 2026
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conditional-fieldset-15547
Conditional Fieldset
Forms & Validation

Conditional Fieldset

Checkbox that unrolls a hidden group of fields beneath it, the extra inputs staying out of the layout until they are needed.

Forms & Validationconditionalrevealcheckboxfieldsetprogressive
lines of CSS
57lines of CSS
dependencies
0dependencies
baseline browsers
Newlybaseline browsers
motion only on interaction
Hovermotion only on interaction
Backdrop
Open a live copy in

Vue, Svelte, styled-components and Tailwind exports are part of Pro. HTML, CSS and React are free forever.

conditional-fieldset-15547.css
.fx-v13-fm-conditional-15546 {
  width: 236px;
  padding: 0.7rem 0.75rem;
  background: #111a2b;
  border: 1px solid #253049;
  border-radius: 0.55rem;
  color: #cbd5e1;
}
.fx-v13-fm-conditional-15546 .tg { display: flex; align-items: center; gap: 0.5rem; font-size: 0.74rem; cursor: pointer; }
.fx-v13-fm-conditional-15546 .tg input { position: absolute; opacity: 0; width: 0; height: 0; }
.fx-v13-fm-conditional-15546 .bx {
  position: relative;
  flex: none;
  width: 17px;
  height: 17px;
  border: 2px solid #475569;
  border-radius: 0.28rem;
  transition: background 0.2s ease, border-color 0.2s ease;
}
.fx-v13-fm-conditional-15546 .bx::after {
  content: '';
  position: absolute;
  left: 4px;
  top: 0px;
  width: 4px;
  height: 8px;
  border: solid #0b1020;
  border-width: 0 2px 2px 0;
  transform: rotate(45deg) scale(0);
  transition: transform 0.2s cubic-bezier(0.34, 1.6, 0.64, 1);
}
.fx-v13-fm-conditional-15546 input:checked + .bx { background: #38bdf8; border-color: #38bdf8; }
.fx-v13-fm-conditional-15546 input:checked + .bx::after { transform: rotate(45deg) scale(1); }
.fx-v13-fm-conditional-15546 .ex {
  display: grid;
  gap: 0.4rem;
  max-height: 0;
  opacity: 0;
  overflow: hidden;
  transition: max-height 0.35s ease, opacity 0.25s ease, margin-top 0.35s ease;
}
.fx-v13-fm-conditional-15546:has(.tg input:checked) .ex { max-height: 130px; opacity: 1; margin-top: 0.6rem; }
.fx-v13-fm-conditional-15546 .ex label { display: block; }
.fx-v13-fm-conditional-15546 .ex span { display: block; margin-bottom: 0.15rem; font-size: 0.61rem; color: #64748b; }
.fx-v13-fm-conditional-15546 .ex input {
  width: 100%;
  padding: 0.32rem 0.5rem;
  font: inherit;
  font-size: 0.73rem;
  color: #e2e8f0;
  background: #0d1424;
  border: 1px solid #29344d;
  border-radius: 0.35rem;
  outline: none;
  transition: border-color 0.2s ease;
}
.fx-v13-fm-conditional-15546 .ex input:focus { border-color: #38bdf8; }
conditional-fieldset-15547.html
<div class="fx-v13-fm-conditional-15546">
  <label class="tg">
    <input type="checkbox" checked />
    <span class="bx"></span>
    <span>Ship to a different address</span>
  </label>
  <div class="ex">
    <label>
      <span>Recipient</span>
      <input value="Mira Tanaka" />
    </label>
    <label>
      <span>Postcode</span>
      <input value="EC1V 9BX" />
    </label>
  </div>
</div>

What do I do with this?

  1. Put conditional-fieldset-15547.css anywhere your page already loads CSS from — in Next.js that is app/globals.css, or any stylesheet with a <link> in your HTML.
  2. Then put the class on the element you want it on: <button class="fx-v13-fm-conditional-15546">. The CSS does nothing until a class name in it matches something on the page.
  • Link the stylesheet, then paste the markup wherever you need it.
npx hoverlab add conditional-fieldset-15547

What's included

  • The markup and the stylesheet, in whichever framework you pick
  • No runtime dependencies

Works with

  • React
  • Vue
  • Svelte
  • Tailwind
  • styled-components
  • Plain CSS

npx hoverlab add conditional-fieldset-15547

Or over MCP, from your editor's agent — no account needed.

License

Free to read, copy and install, for personal and non-commercial projects. Shipping it in client work or a paid product needs Pro ($79 once). The source lands in your repo and stops being ours — no attribution, nothing to upgrade.

Was this useful?

Motion safety

Static estimate, read from the CSS

Reduced motion
Brief motion, no guard

Animates briefly or on interaction. Only looping motion gets a guard in this catalog; copy the one from the Insights tab if this ships on a critical path.

What it animates
Reflows

Animates margin-top, max-height (and background, border-color). The browser re-lays-out the page on every frame; prefer transform if you can.

Flashing (WCAG 2.3.1)
No flashing found

No repeating change in opacity, colour or brightness large enough to count as a flash.

Layout shift (CLS)
May shift layout

Animates margin-top, max-height on a box in flow, so content beside or after it can move. A category from the CSS, not a measurement for this effect.

Every row is read from the shipped CSS. Only a figure marked measured came from a browser. Customizing the speed changes the timing, so recheck a customized copy. How it is computed

33 more effects in Forms & Validation

All of them free to read, copy and install — no account, no locked tiles, no watermarked preview. The whole catalog is open, and so are the API and the CLI.

Browse Forms & Validation

Shipping one commercially

Copying the code is free. Putting it in client work or a paid product is what Pro is for — the licence, not the access.

  • A commercial licence for everything in the catalog
  • Unlimited bundle exports, in Vue, Svelte and Tailwind
  • One payment — no subscription, nothing to renew
Pro — $79 once

7 variations of Conditional Fieldset

Finished looks, each one a position in the customizer above. Copy any of them, or open it and keep moving the sliders.