:has() Parent Interactions

:root {
  --bg: #0c0d10;
  --surface: #15161b;
  --surface-2: #1d1f27;
  --ink: #e9eaf0;
  --muted: #9a9cab;
  --accent: #8b5cf6;
  --accent-2: #22d3ee;
  --ok: #34d399;
  --warn: #fbbf24;
  --danger: #f87171;
  --line: rgba(255, 255, 255, 0.1);
  --line-2: rgba(255, 255, 255, 0.18);
  --r-sm: 8px;
  --r-md: 12px;
  --r-lg: 16px;
}

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

html {
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

body {
  margin: 0;
  background:
    radial-gradient(1100px 620px at 82% -8%, rgba(139, 92, 246, 0.16), transparent 60%),
    radial-gradient(900px 520px at 8% 108%, rgba(34, 211, 238, 0.1), transparent 55%),
    var(--bg);
  color: var(--ink);
  font-family: "Inter", system-ui, -apple-system, sans-serif;
  line-height: 1.5;
  min-height: 100vh;
}

code,
.mono {
  font-family: "JetBrains Mono", ui-monospace, monospace;
}

.wrap {
  max-width: 1040px;
  margin: 0 auto;
  padding: 40px 20px 64px;
}

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

/* ---------- masthead ---------- */
.masthead {
  margin-bottom: 22px;
}

.eyebrow {
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--accent-2);
  margin-bottom: 10px;
}

h1 {
  font-size: clamp(26px, 5vw, 40px);
  font-weight: 700;
  letter-spacing: -0.02em;
  margin: 0 0 12px;
}

h1 code {
  color: var(--accent);
}

.lede {
  max-width: 66ch;
  color: var(--muted);
  margin: 0 0 16px;
  font-size: 15px;
}

.lede code {
  color: var(--ink);
  background: var(--surface-2);
  padding: 1px 6px;
  border-radius: 6px;
  font-size: 13px;
}

.support {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  font-weight: 500;
  padding: 7px 12px;
  border-radius: 999px;
  border: 1px solid var(--line);
  background: var(--surface);
}

.support::before {
  content: "";
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--warn);
}

.support.ok::before {
  background: var(--ok);
  box-shadow: 0 0 0 4px rgba(52, 211, 153, 0.16);
}

.support.no::before {
  background: var(--danger);
}

/* ---------- readout ---------- */
.readout {
  display: flex;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
  margin: 18px 0 26px;
  padding: 14px 16px;
  background: linear-gradient(180deg, var(--surface-2), var(--surface));
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  box-shadow: 0 1px 0 rgba(255, 255, 255, 0.04) inset;
}

.readout .dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 0 0 4px rgba(139, 92, 246, 0.18);
  transition: background 0.2s ease, box-shadow 0.2s ease;
}

.readout.hot .dot {
  background: var(--accent-2);
  box-shadow: 0 0 0 4px rgba(34, 211, 238, 0.22);
}

.readout-label {
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--muted);
}

.readout code {
  flex: 1;
  min-width: 200px;
  font-size: 13px;
  color: var(--accent-2);
  overflow-x: auto;
  white-space: nowrap;
}

/* ---------- panels ---------- */
.panels {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 18px;
}

.panel {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  padding: 20px;
  transition: border-color 0.2s ease;
}

.panel:hover {
  border-color: var(--line-2);
}

.panel-head {
  margin-bottom: 16px;
}

.panel-head h2 {
  font-size: 16px;
  font-weight: 600;
  margin: 0 0 4px;
}

.panel-head p {
  margin: 0;
  font-size: 13px;
  color: var(--muted);
}

.panel code,
.form-note code,
.plan-status code,
.foot code {
  font-size: 12px;
  color: var(--accent-2);
  background: var(--surface-2);
  padding: 1px 5px;
  border-radius: 5px;
}

/* ---------- 1. form ---------- */
.signup {
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.field {
  display: flex;
  flex-direction: column;
  gap: 6px;
  padding: 12px;
  border: 1px solid var(--line);
  border-left: 3px solid var(--line);
  border-radius: var(--r-md);
  background: var(--surface-2);
  transition: border-color 0.2s ease, box-shadow 0.2s ease, background 0.2s ease;
}

.field-label {
  font-size: 13px;
  font-weight: 600;
}

.field input {
  width: 100%;
  padding: 9px 11px;
  font: inherit;
  font-size: 14px;
  color: var(--ink);
  background: var(--bg);
  border: 1px solid var(--line-2);
  border-radius: var(--r-sm);
  outline: none;
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
}

.field input::placeholder {
  color: #5c5e6c;
}

.field input:focus-visible {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px rgba(139, 92, 246, 0.28);
}

.hint {
  font-size: 12px;
  color: var(--muted);
}

/* the star of the show: parent styled from its input */
.field:has(input:user-invalid) {
  border-color: var(--danger);
  border-left-color: var(--danger);
  background: rgba(248, 113, 113, 0.07);
}

.field:has(input:user-invalid) .hint::after {
  content: " \2014 check this field";
  color: var(--danger);
}

.field:has(input:valid:not(:placeholder-shown)) {
  border-color: var(--ok);
  border-left-color: var(--ok);
  background: rgba(52, 211, 153, 0.07);
}

.field:has(input:valid:not(:placeholder-shown)) .field-label::after {
  content: " \2713";
  color: var(--ok);
}

.check {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 14px;
  padding: 6px 2px;
  border-radius: var(--r-sm);
  cursor: pointer;
  transition: color 0.2s ease;
}

.check input {
  width: 17px;
  height: 17px;
  accent-color: var(--accent);
  flex: none;
}

.check:has(input:checked) {
  color: var(--ok);
}

.submit {
  margin-top: 2px;
  padding: 11px 16px;
  font: inherit;
  font-weight: 600;
  font-size: 14px;
  color: #fff;
  background: var(--surface-2);
  border: 1px solid var(--line-2);
  border-radius: var(--r-md);
  cursor: not-allowed;
  opacity: 0.55;
  transition: all 0.2s ease;
}

/* whole-form gating with chained :has() */
.signup:has(input:valid):has(input[name="pw"]:valid):has(input[name="terms"]:checked) .submit {
  cursor: pointer;
  opacity: 1;
  background: linear-gradient(135deg, var(--accent), #6d3ff0);
  border-color: transparent;
  box-shadow: 0 8px 24px rgba(139, 92, 246, 0.35);
}

.signup:has(.submit:not([disabled]):hover) .submit,
.submit:hover {
  filter: brightness(1.08);
}

.form-note {
  margin: 2px 0 0;
  font-size: 12px;
  color: var(--muted);
}

/* ---------- 2. spotlight grid ---------- */
.grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 12px;
}

.card {
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  background: var(--surface-2);
  cursor: pointer;
  outline: none;
  transition: transform 0.22s ease, filter 0.22s ease, opacity 0.22s ease,
    border-color 0.22s ease, box-shadow 0.22s ease;
}

.card-tag {
  display: inline-block;
  font-size: 10px;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent-2);
  background: rgba(34, 211, 238, 0.12);
  padding: 2px 7px;
  border-radius: 999px;
  margin-bottom: 8px;
}

.card h3 {
  margin: 0 0 4px;
  font-size: 15px;
  font-weight: 600;
}

.card p {
  margin: 0;
  font-size: 12px;
  color: var(--muted);
}

/* dim siblings when any card is hovered/focused */
.grid:has(.card:hover) .card:not(:hover),
.grid:has(.card:focus-visible) .card:not(:focus-visible) {
  filter: saturate(0.35) brightness(0.7);
  opacity: 0.55;
  transform: scale(0.98);
}

.card:hover,
.card:focus-visible {
  border-color: var(--accent);
  box-shadow: 0 12px 30px rgba(0, 0, 0, 0.4);
  transform: translateY(-3px);
}

/* ---------- 3. count-aware layout ---------- */
.plans {
  border: 0;
  margin: 0;
  padding: 0;
  display: grid;
  grid-template-columns: 1fr;
  gap: 10px;
  transition: grid-template-columns 0.25s ease;
}

.plan {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px 14px;
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  background: var(--surface-2);
  cursor: pointer;
  transition: border-color 0.2s ease, background 0.2s ease;
}

.plan input {
  width: 17px;
  height: 17px;
  accent-color: var(--accent);
  flex: none;
}

.plan-name {
  font-weight: 600;
  font-size: 14px;
}

.plan-price {
  margin-left: auto;
  font-family: "JetBrains Mono", monospace;
  font-size: 13px;
  color: var(--muted);
}

.plan:has(input:checked) {
  border-color: var(--accent);
  background: rgba(139, 92, 246, 0.12);
}

.plan:has(input:checked) .plan-price {
  color: var(--accent-2);
}

/* 2 checked -> two columns */
.plans:has(input:checked ~ label input:checked) {
  grid-template-columns: repeat(2, 1fr);
}

/* 3+ checked -> highlight the whole fieldset */
.plans:has(input:checked ~ label input:checked ~ label input:checked) {
  padding: 8px;
  border-radius: var(--r-md);
  background: rgba(34, 211, 238, 0.06);
  outline: 1px solid rgba(34, 211, 238, 0.25);
}

.plan-status {
  margin: 12px 0 0;
  font-size: 13px;
  color: var(--muted);
}

/* ---------- 4. tabs + accordion ---------- */
.tabs {
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  overflow: hidden;
  margin-bottom: 16px;
}

.tabstrip {
  display: flex;
  gap: 4px;
  padding: 6px;
  background: var(--surface-2);
  border-bottom: 1px solid var(--line);
}

.tabstrip label {
  flex: 1;
  text-align: center;
  padding: 8px 10px;
  font-size: 13px;
  font-weight: 500;
  color: var(--muted);
  border-radius: var(--r-sm);
  cursor: pointer;
  transition: background 0.18s ease, color 0.18s ease;
}

.tabstrip label:hover {
  color: var(--ink);
}

.tabstrip input:checked + label {
  background: var(--accent);
  color: #fff;
}

.tabstrip input:focus-visible + label {
  box-shadow: 0 0 0 3px rgba(139, 92, 246, 0.4);
}

.tabpanels {
  padding: 14px;
  font-size: 13px;
  color: var(--muted);
}

.tabpanel {
  display: none;
}

.tabpanel p {
  margin: 0;
}

/* reveal panels using :has(:checked) on the wrapper */
.tabs:has(#tab-a:checked) .tabpanel[data-for="tab-a"],
.tabs:has(#tab-b:checked) .tabpanel[data-for="tab-b"],
.tabs:has(#tab-c:checked) .tabpanel[data-for="tab-c"] {
  display: block;
  animation: fade 0.2s ease;
}

@keyframes fade {
  from {
    opacity: 0;
    transform: translateY(4px);
  }
}

.accordion {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

details-row {
  display: block;
}

.acc-item {
  display: grid;
  grid-template-columns: 1fr auto;
  align-items: start;
  gap: 4px 12px;
  padding: 12px 14px;
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  background: var(--surface-2);
  cursor: pointer;
  transition: border-color 0.2s ease;
}

.acc-item:hover {
  border-color: var(--line-2);
}

.acc-summary {
  font-size: 13px;
  font-weight: 600;
  grid-column: 1;
}

.acc-body {
  grid-column: 1 / -1;
  font-size: 12px;
  color: var(--muted);
  max-height: 0;
  overflow: hidden;
  opacity: 0;
  transition: max-height 0.28s ease, opacity 0.28s ease, margin 0.28s ease;
}

.chevron {
  grid-column: 2;
  grid-row: 1;
  width: 10px;
  height: 10px;
  border-right: 2px solid var(--muted);
  border-bottom: 2px solid var(--muted);
  transform: rotate(45deg);
  transition: transform 0.25s ease, border-color 0.25s ease;
  margin-top: 3px;
}

.acc-item:has(input:checked) {
  border-color: var(--accent);
}

.acc-item:has(input:checked) .acc-body {
  max-height: 120px;
  opacity: 1;
  margin-top: 4px;
}

.acc-item:has(input:checked) .chevron {
  transform: rotate(-135deg);
  border-color: var(--accent);
}

/* ---------- foot ---------- */
.foot {
  margin-top: 26px;
  font-size: 12px;
  color: var(--muted);
  text-align: center;
}

/* ---------- fallback when :has() unsupported ---------- */
@supports not selector(:has(*)) {
  .no-has .field,
  .no-has .plan,
  .no-has .acc-item {
    border-left-color: var(--line);
  }
  .no-has .submit {
    opacity: 1;
    cursor: pointer;
    background: linear-gradient(135deg, var(--accent), #6d3ff0);
    border-color: transparent;
  }
  .no-has .tabpanel {
    display: block;
    border-top: 1px dashed var(--line);
    padding-top: 8px;
    margin-top: 8px;
  }
  .no-has .acc-body {
    max-height: none;
    opacity: 1;
    margin-top: 6px;
  }
}

/* ---------- responsive ---------- */
@media (max-width: 820px) {
  .panels {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 520px) {
  .wrap {
    padding: 28px 14px 48px;
  }
  .grid {
    grid-template-columns: 1fr;
  }
  .readout code {
    min-width: 100%;
  }
}

@media (prefers-reduced-motion: reduce) {
  * {
    animation: none !important;
    transition: none !important;
  }
}

// script.js — JS only mirrors the live :has() state into the readout.
// All actual UI behavior is pure CSS via :has(). No event-driven styling here.
(function () {
  "use strict";

  var supportsHas =
    typeof CSS !== "undefined" &&
    CSS.supports &&
    CSS.supports("selector(:has(*))");

  // ---- feature detect banner ----
  var banner = document.getElementById("support");
  if (supportsHas) {
    banner.classList.add("ok");
    banner.textContent = "Native :has() is active — every panel is CSS-driven.";
  } else {
    banner.classList.add("no");
    banner.textContent =
      "This browser lacks :has() — showing a static accessible fallback.";
    document.body.classList.add("no-has");
    // still wire the readout so the label isn't stale
    document.getElementById("selector").textContent =
      "/* :has() unsupported — fallback styling applied */";
    return;
  }

  var readout = document.querySelector(".readout");
  var selectorEl = document.getElementById("selector");
  var form = document.getElementById("signup");
  var plans = document.getElementById("plans");
  var planStatus = document.getElementById("plan-status");
  var grid = document.querySelector(".grid");
  var tabInputs = document.querySelectorAll('input[name="tabs"]');

  var idleText = ":root { /* interact to see :has() fire */ }";
  var idleTimer = null;

  function show(rule, hot) {
    selectorEl.textContent = rule;
    readout.classList.toggle("hot", !!hot);
    if (idleTimer) clearTimeout(idleTimer);
    idleTimer = setTimeout(function () {
      selectorEl.textContent = idleText;
      readout.classList.remove("hot");
    }, 2600);
  }

  // ---- 1. form: report which rule the field wrappers match ----
  function reportForm() {
    var email = form.querySelector('input[name="email"]');
    var pw = form.querySelector('input[name="pw"]');
    var terms = form.querySelector('input[name="terms"]');

    var invalid = form.querySelector("input:user-invalid");
    if (invalid) {
      show(".field:has(input:user-invalid) { border-color: danger }", false);
      return;
    }
    var complete =
      email.validity.valid &&
      email.value &&
      pw.validity.valid &&
      pw.value &&
      terms.checked;
    if (complete) {
      show(
        "form:has(:valid):has([name=terms]:checked) .submit { unlocked }",
        true
      );
    } else {
      show(".field:has(input:valid:not(:placeholder-shown)) { ok }", true);
    }
  }
  form.addEventListener("input", reportForm);
  form.addEventListener("blur", reportForm, true);
  form.addEventListener("submit", function (e) {
    e.preventDefault();
    var btn = form.querySelector(".submit");
    var label = btn.textContent;
    btn.textContent = "Account created ✓";
    show("form:has(:valid):has([name=terms]:checked) — submitted", true);
    setTimeout(function () {
      btn.textContent = label;
    }, 1600);
  });

  // ---- 2. spotlight grid ----
  grid.addEventListener("pointerover", function (e) {
    if (e.target.closest(".card")) {
      show(".grid:has(.card:hover) .card:not(:hover) { dimmed }", true);
    }
  });
  grid.addEventListener("focusin", function (e) {
    if (e.target.closest(".card")) {
      show(".grid:has(.card:focus-visible) .card:not(:focus-visible) { dimmed }", true);
    }
  });

  // ---- 3. count-aware layout ----
  function reportPlans() {
    var n = plans.querySelectorAll("input:checked").length;
    var msg, rule;
    if (n === 0) {
      msg = "Nothing selected — single-column stack.";
      rule = ".plans { grid-template-columns: 1fr }";
    } else if (n === 1) {
      msg = "1 plan selected — still one column.";
      rule = ".plan:has(input:checked) { highlighted }";
    } else if (n === 2) {
      msg = "2 plans — layout splits into two columns.";
      rule = ".plans:has(input:checked ~ label input:checked) { 2 cols }";
    } else {
      msg = n + " plans — comparison mode with cyan outline.";
      rule =
        ".plans:has(:checked ~ label :checked ~ label :checked) { compare }";
    }
    planStatus.textContent = msg;
    show(rule, n > 0);
  }
  plans.addEventListener("change", reportPlans);

  // ---- 4. tabs (readout only; CSS does the switching) ----
  tabInputs.forEach(function (input) {
    input.addEventListener("change", function () {
      var name = input.nextElementSibling.textContent.trim();
      show(".tabs:has(#" + input.id + ":checked) .tabpanel { show " + name + " }", true);
    });
  });

  // accordion readout
  document.querySelectorAll(".acc-item input").forEach(function (input) {
    input.addEventListener("change", function () {
      show(
        ".acc-item:has(input:checked) .acc-body { expand }",
        input.checked
      );
    });
  });
})();

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1" />
  <title>:has() Parent Interactions</title>
  <link rel="preconnect" href="https://fonts.googleapis.com" />
  <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
  <link
    href="https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&family=JetBrains+Mono:wght@400;500&display=swap"
    rel="stylesheet"
  />
  <link rel="stylesheet" href="style.css" />
</head>
<body>
  <main class="wrap">
    <header class="masthead">
      <div class="eyebrow">CSS &bull; relational selector</div>
      <h1><code>:has()</code> Parent Interactions</h1>
      <p class="lede">
        Four demos styled by descendants, not JavaScript. The parent reacts to
        what lives inside it &mdash; invalid inputs, hovered siblings, the count
        of checked options, and no-JS tabs. The live readout below mirrors the
        exact <code>:has()</code> rule firing right now.
      </p>
      <div id="support" class="support" role="status" aria-live="polite"></div>
    </header>

    <!-- readout -->
    <section class="readout" aria-label="Live selector readout">
      <span class="dot" aria-hidden="true"></span>
      <span class="readout-label">Active rule</span>
      <code id="selector">:root { /* interact to see :has() fire */ }</code>
    </section>

    <div class="panels">
      <!-- 1. Form validation -->
      <section class="panel" aria-labelledby="p1-title">
        <div class="panel-head">
          <h2 id="p1-title">1 &middot; Self-highlighting form</h2>
          <p>Each <code>.field</code> restyles itself from the input it wraps.</p>
        </div>
        <form id="signup" class="signup" novalidate>
          <label class="field">
            <span class="field-label">Work email</span>
            <input type="email" name="email" placeholder="[email protected]" required />
            <span class="hint">We validate the format live via <code>:user-invalid</code>.</span>
          </label>
          <label class="field">
            <span class="field-label">Password</span>
            <input type="password" name="pw" placeholder="8+ characters" minlength="8" required />
            <span class="hint">Turns green once valid.</span>
          </label>
          <label class="check">
            <input type="checkbox" name="terms" required />
            <span>I accept the terms of service</span>
          </label>
          <button type="submit" class="submit">Create account</button>
          <p class="form-note">
            The button unlocks only when
            <code>form:has(:valid):has(input[name=terms]:checked)</code>.
          </p>
        </form>
      </section>

      <!-- 2. Sibling dimming grid -->
      <section class="panel" aria-labelledby="p2-title">
        <div class="panel-head">
          <h2 id="p2-title">2 &middot; Spotlight grid</h2>
          <p>Hover one card &mdash; <code>:has(.card:hover)</code> dims the rest.</p>
        </div>
        <div class="grid" role="list">
          <article class="card" role="listitem" tabindex="0">
            <span class="card-tag">Edge</span>
            <h3>Nova CDN</h3>
            <p>312 POPs, 8ms median TTFB worldwide.</p>
          </article>
          <article class="card" role="listitem" tabindex="0">
            <span class="card-tag">Data</span>
            <h3>Atlas DB</h3>
            <p>Serverless Postgres with branchable snapshots.</p>
          </article>
          <article class="card" role="listitem" tabindex="0">
            <span class="card-tag">Auth</span>
            <h3>Gatekeep</h3>
            <p>Passkeys, SSO and device trust in one SDK.</p>
          </article>
          <article class="card" role="listitem" tabindex="0">
            <span class="card-tag">Queue</span>
            <h3>Relay MQ</h3>
            <p>At-least-once delivery, 1M msg/s per shard.</p>
          </article>
        </div>
      </section>

      <!-- 3. Quantity-driven layout -->
      <section class="panel" aria-labelledby="p3-title">
        <div class="panel-head">
          <h2 id="p3-title">3 &middot; Count-aware layout</h2>
          <p>The grid reflows by how many plans are checked.</p>
        </div>
        <fieldset class="plans" id="plans">
          <legend class="sr-only">Choose your plans</legend>
          <label class="plan">
            <input type="checkbox" name="plan" value="hobby" />
            <span class="plan-name">Hobby</span>
            <span class="plan-price">$0</span>
          </label>
          <label class="plan">
            <input type="checkbox" name="plan" value="pro" />
            <span class="plan-name">Pro</span>
            <span class="plan-price">$24</span>
          </label>
          <label class="plan">
            <input type="checkbox" name="plan" value="team" />
            <span class="plan-name">Team</span>
            <span class="plan-price">$79</span>
          </label>
          <label class="plan">
            <input type="checkbox" name="plan" value="scale" />
            <span class="plan-name">Scale</span>
            <span class="plan-price">$199</span>
          </label>
        </fieldset>
        <p class="plan-status" id="plan-status">Nothing selected &mdash; single-column stack.</p>
      </section>

      <!-- 4. No-JS tabs + accordion -->
      <section class="panel" aria-labelledby="p4-title">
        <div class="panel-head">
          <h2 id="p4-title">4 &middot; No-JS tabs &amp; accordion</h2>
          <p>Radios and checkboxes drive state via <code>:has(:checked)</code>.</p>
        </div>

        <div class="tabs">
          <div class="tabstrip" role="tablist">
            <input type="radio" id="tab-a" name="tabs" class="sr-only" checked />
            <label for="tab-a">Overview</label>
            <input type="radio" id="tab-b" name="tabs" class="sr-only" />
            <label for="tab-b">Metrics</label>
            <input type="radio" id="tab-c" name="tabs" class="sr-only" />
            <label for="tab-c">Changelog</label>
          </div>
          <div class="tabpanels">
            <div class="tabpanel" data-for="tab-a">
              <p>A <code>.tabs</code> wrapper checks <code>:has(#tab-a:checked)</code>
              and reveals this panel &mdash; zero listeners.</p>
            </div>
            <div class="tabpanel" data-for="tab-b">
              <p>Uptime 99.98%, p95 latency 42ms, 1.2B requests this month.</p>
            </div>
            <div class="tabpanel" data-for="tab-c">
              <p>v4.2 shipped native <code>:has()</code> feature detection and
              donut-scope theming.</p>
            </div>
          </div>
        </div>

        <div class="accordion">
          <details-row>
            <label class="acc-item">
              <input type="checkbox" class="sr-only" />
              <span class="acc-summary">Does <code>:has()</code> hurt performance?</span>
              <span class="acc-body">Modern engines optimize it well for the
              common child and state cases used here.</span>
              <span class="chevron" aria-hidden="true"></span>
            </label>
          </details-row>
          <details-row>
            <label class="acc-item">
              <input type="checkbox" class="sr-only" />
              <span class="acc-summary">Can I select a parent finally?</span>
              <span class="acc-body">Yes &mdash; <code>:has()</code> matches an
              element based on its descendants, effectively a parent selector.</span>
              <span class="chevron" aria-hidden="true"></span>
            </label>
          </details-row>
        </div>
      </section>
    </div>

    <footer class="foot">
      Built with the native CSS <code>:has()</code> relational pseudo-class.
      JavaScript only mirrors state into the readout.
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