Layout behavior lab

<main class="layout-lab" data-layout-lab data-mode="grid" data-density="normal">
  <header class="lab-header">
    <p class="eyebrow">Layout decision</p>
    <h1>Same content, different layout ownership</h1>
    <p>Change the available slot and content pressure to see when the primitive becomes part of the maintenance problem.</p>
  </header>

  <form class="control-panel" aria-label="Layout behavior controls">
    <fieldset class="control-group">
      <legend>Layout mode</legend>
      <div class="segmented">
        <label><input type="radio" name="mode" value="flex" /> Flex wrap</label>
        <label><input type="radio" name="mode" value="grid" checked /> Grid tracks</label>
        <label><input type="radio" name="mode" value="query" /> Container query</label>
      </div>
    </fieldset>

    <label class="control-group">
      <span>Content pressure</span>
      <select name="density">
        <option value="normal">Normal cards</option>
        <option value="dense">Dense metadata</option>
        <option value="long">Long production labels</option>
      </select>
    </label>

    <label class="control-group">
      <span>Component slot <strong data-width-label>760px</strong></span>
      <input type="range" name="width" min="360" max="860" value="760" />
    </label>
  </form>

  <section class="stage" aria-label="Layout preview">
    <div class="stage__measure" data-stage>
      <div class="work-list">
        <article class="work-card work-card--primary">
          <div>
            <p class="work-card__meta">Release risk</p>
            <h2 data-card-title>Checkout summary</h2>
          </div>
          <p class="work-card__detail">Needs amount, tax, discount, and payment method visible before confirmation.</p>
          <a href="#preview">Review</a>
        </article>
        <article class="work-card">
          <div>
            <p class="work-card__meta">Support queue</p>
            <h2 data-card-title>Refund states</h2>
          </div>
          <p class="work-card__detail">Includes pending, partial, failed, and manual approval states.</p>
          <a href="#preview">Inspect</a>
        </article>
        <article class="work-card">
          <div>
            <p class="work-card__meta">Localization</p>
            <h2 data-card-title>German labels</h2>
          </div>
          <p class="work-card__detail">Longest strings should wrap without pushing actions out of reach.</p>
          <a href="#preview">Compare</a>
        </article>
      </div>
    </div>
  </section>

  <aside class="diagnosis" aria-live="polite">
    <p class="eyebrow">Reading the result</p>
    <h2 data-verdict>Grid is the strongest default here.</h2>
    <p data-reason>Cards need predictable columns and aligned actions, so the two-axis relationship matters more than simple distribution.</p>
    <ul data-checks>
      <li>Tracks absorb unequal text without changing the component contract.</li>
      <li>Actions remain visually comparable across rows.</li>
    </ul>
  </aside>
</main>

.layout-lab {
  --ink: #17212b;
  --muted: #526160;
  --line: #c8d4d1;
  --surface: #fffdf8;
  --panel: #f2f7f4;
  --accent: #0d6f67;
  display: grid;
  gap: 1rem;
  max-width: 68rem;
  margin: 0 auto;
  padding: 1.25rem;
  color: var(--ink);
}

.lab-header {
  display: grid;
  gap: 0.35rem;
  max-width: 52rem;
}

.eyebrow,
.work-card__meta {
  margin: 0;
  color: var(--accent);
  font-size: 0.76rem;
  font-weight: 800;
  letter-spacing: 0;
  text-transform: uppercase;
}

h1,
h2,
p {
  margin-block: 0;
}

h1 {
  font-size: clamp(1.8rem, 5vw, 3.2rem);
  line-height: 1.02;
}

.control-panel {
  display: grid;
  gap: 0.75rem;
  grid-template-columns: repeat(auto-fit, minmax(14rem, 1fr));
  align-items: end;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  padding: 0.85rem;
}

.control-group {
  display: grid;
  gap: 0.45rem;
  margin: 0;
  border: 0;
  padding: 0;
  color: var(--muted);
  font-weight: 700;
}

.control-group strong {
  color: var(--ink);
}

.segmented {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
}

.segmented label {
  position: relative;
  min-height: 2.4rem;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: #ffffff;
  padding: 0.55rem 0.7rem;
  color: var(--ink);
  cursor: pointer;
}

.segmented input {
  position: absolute;
  inline-size: 1px;
  block-size: 1px;
  opacity: 0;
}

.segmented label:has(input:checked) {
  border-color: var(--accent);
  background: #dff0ec;
}

select,
input[type='range'] {
  width: 100%;
}

select {
  min-height: 2.45rem;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: #ffffff;
  padding-inline: 0.65rem;
}

input[type='range'] {
  accent-color: var(--accent);
}

.stage {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: linear-gradient(90deg, #eef4f1 1px, transparent 1px), #f8faf8;
  background-size: 24px 24px;
  padding: 1rem;
  overflow-x: auto;
}

.stage__measure {
  --stage-width: 760px;
  container-type: inline-size;
  max-width: min(100%, var(--stage-width));
  min-width: min(100%, 20rem);
  margin-inline: auto;
  border: 1px dashed #97aaa5;
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.72);
  padding: 0.75rem;
}

.work-list {
  display: grid;
  gap: 0.75rem;
}

.work-card {
  display: grid;
  gap: 0.8rem;
  align-content: space-between;
  min-width: 0;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  padding: 0.9rem;
}

.work-card h2 {
  margin-block-start: 0.25rem;
  font-size: 1.15rem;
  line-height: 1.12;
  overflow-wrap: anywhere;
}

.work-card__detail {
  display: none;
  color: var(--muted);
  font-size: 0.92rem;
  line-height: 1.45;
}

.work-card a {
  justify-self: start;
  border: 1px solid var(--ink);
  border-radius: 6px;
  color: var(--ink);
  padding: 0.45rem 0.65rem;
  text-decoration: none;
}

[data-density='dense'] .work-card__detail,
[data-density='long'] .work-card__detail {
  display: block;
}

[data-mode='flex'] .work-list {
  display: flex;
  flex-wrap: wrap;
  align-items: stretch;
}

[data-mode='flex'] .work-card {
  flex: 1 1 14rem;
}

[data-mode='grid'] .work-list {
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 14rem), 1fr));
}

[data-mode='query'] .work-list {
  grid-template-columns: 1fr;
}

@container (min-width: 40rem) {
  [data-mode='query'] .work-list {
    grid-template-columns: 1.25fr 1fr;
  }

  [data-mode='query'] .work-card--primary {
    grid-row: span 2;
  }
}

@container (min-width: 58rem) {
  [data-mode='query'] .work-list {
    grid-template-columns: 1.4fr 1fr 1fr;
  }
}

.diagnosis {
  display: grid;
  gap: 0.55rem;
  border-inline-start: 4px solid var(--accent);
  background: var(--panel);
  padding: 0.95rem 1rem;
}

.diagnosis h2 {
  font-size: 1.25rem;
}

.diagnosis ul {
  display: grid;
  gap: 0.35rem;
  margin: 0;
  padding-inline-start: 1.1rem;
  color: var(--muted);
}

const lab = document.querySelector('[data-layout-lab]');
const form = lab.querySelector('form');
const stage = lab.querySelector('[data-stage]');
const widthLabel = lab.querySelector('[data-width-label]');
const titles = Array.from(lab.querySelectorAll('[data-card-title]'));
const verdict = lab.querySelector('[data-verdict]');
const reason = lab.querySelector('[data-reason]');
const checks = lab.querySelector('[data-checks]');

const cardTitles = {
  normal: ['Checkout summary', 'Refund states', 'German labels'],
  dense: ['Checkout summary with applied promotions', 'Refund states across payment providers', 'German labels in account settings'],
  long: [
    'Checkout summary with unavailable payment methods and stacked promotion rules',
    'Refund states across payment providers, manual review, and failed captures',
    'German labels for account-level notification preferences and billing history',
  ],
};

const notes = {
  flex: {
    verdict: 'Flexbox is useful only while the job stays one-axis.',
    reason: 'Wrapping distributes cards into available space, but row alignment becomes a side effect once content lengths diverge.',
    checks: [
      'Good for a toolbar or a loose list of chips.',
      'Risky when cards need comparable columns, metadata, or action placement.',
    ],
  },
  grid: {
    verdict: 'Grid is the strongest default here.',
    reason: 'Cards need predictable columns and aligned actions, so the two-axis relationship matters more than simple distribution.',
    checks: [
      'Tracks absorb unequal text without changing the component contract.',
      'Actions remain visually comparable across rows.',
    ],
  },
  query: {
    verdict: 'Container queries make the component own the breakpoint.',
    reason: 'The preview changes at the card rail width, not at the viewport, which is the safer rule for reusable components.',
    checks: [
      'Use this when the same component appears in a sidebar, modal, and wide page slot.',
      'Keep page-level media queries for the surrounding shell.',
    ],
  },
};

function renderList(items) {
  checks.replaceChildren();
  items.forEach((item) => {
    const li = document.createElement('li');
    li.textContent = item;
    checks.append(li);
  });
}

function render() {
  const values = new FormData(form);
  const mode = values.get('mode') || 'grid';
  const density = values.get('density') || 'normal';
  const width = Number(values.get('width') || 760);
  const activeNotes = notes[mode];

  lab.dataset.mode = mode;
  lab.dataset.density = density;
  stage.style.setProperty('--stage-width', width + 'px');
  widthLabel.textContent = width + 'px';

  cardTitles[density].forEach((title, index) => {
    titles[index].textContent = title;
  });

  verdict.textContent = activeNotes.verdict;
  reason.textContent = activeNotes.reason;

  const extraCheck = width < 520 && density !== 'normal'
    ? 'At this width, the layout also needs overflow-wrap, stable actions, and a clear wrapping policy.'
    : 'The layout decision should still be tested with the longest expected content.';

  renderList(activeNotes.checks.concat(extraCheck));
}

form.addEventListener('input', render);
render();