RTL mirror: logical anchor sides

<main class="demo">
  <header class="intro">
    <h1>Mirror it</h1>
    <p>
      Every tooltip, timestamp, badge, hint and menu here is placed with logical
      <code>data-⚓️-*</code> sides: <code>before</code>, <code>after</code>,
      <code>align-trailing</code>. Flip <code>dir</code> on <code>&lt;html&gt;</code> and the whole UI mirrors
      with zero RTL CSS; the button only changes that one attribute.
    </p>
  </header>

  <div class="bar">
    <button class="flip" type="button" aria-pressed="false">
      <span class="flip-icon" aria-hidden="true">⇄</span>
      <code class="flip-label" dir="ltr">dir="<span class="flip-value">ltr</span>"</code>
    </button>
    <label class="xray-toggle"><input type="checkbox" id="xray"> X-ray</label>
  </div>

  <div class="app" data-⚓️-root>
    <nav class="rail" aria-label="Sections">
      <ul>
        <li data-⚓️-scope-name="--nav">
          <a href="#" data-⚓️-name="--nav" aria-label="Inbox">
            <svg viewBox="0 0 24 24" aria-hidden="true"><path d="M4 13h4l2 3h4l2-3h4M4 13l2-7h12l2 7v5H4z"/></svg>
          </a>
          <span class="tip" data-⚓️-to="--nav" data-⚓️-side="after" data-⚓️-align-y="center" aria-hidden="true">Inbox</span>
        </li>
        <li data-⚓️-scope-name="--nav">
          <a href="#" data-⚓️-name="--nav" aria-label="Messages" aria-current="page">
            <svg viewBox="0 0 24 24" aria-hidden="true"><path d="M4 5h16v11H9l-5 4z"/></svg>
          </a>
          <span class="tip" data-⚓️-to="--nav" data-⚓️-side="after" data-⚓️-align-y="center" aria-hidden="true">Messages</span>
        </li>
        <li data-⚓️-scope-name="--nav">
          <a href="#" data-⚓️-name="--nav" aria-label="Calendar">
            <svg viewBox="0 0 24 24" aria-hidden="true"><path d="M4 6h16v14H4zM4 10h16M8 3v5M16 3v5"/></svg>
          </a>
          <span class="tip" data-⚓️-to="--nav" data-⚓️-side="after" data-⚓️-align-y="center" aria-hidden="true">Calendar</span>
        </li>
        <li data-⚓️-scope-name="--nav">
          <a href="#" data-⚓️-name="--nav" aria-label="Settings">
            <svg viewBox="0 0 24 24" aria-hidden="true"><circle cx="12" cy="12" r="3"/><path d="M12 2v3M12 19v3M2 12h3M19 12h3M5 5l2 2M17 17l2 2M5 19l2-2M17 7l2-2"/></svg>
          </a>
          <span class="tip" data-⚓️-to="--nav" data-⚓️-side="after" data-⚓️-align-y="center" aria-hidden="true">Settings</span>
        </li>
      </ul>
    </nav>

    <section class="chat" aria-label="Conversation with Noor">
      <header class="chat-head">
        <span class="avatar" data-⚓️-name="--avatar" aria-hidden="true">N</span>
        <span class="online" data-⚓️-to="--avatar" data-⚓️-align-trailing data-⚓️-align-bottom aria-hidden="true"></span>
        <span class="who"><b>Noor</b><small>online</small></span>
        <button class="more" type="button" popovertarget="menu" data-⚓️-name="--more" aria-label="Conversation options">⋯</button>
      </header>

      <ol class="thread">
        <li class="in" data-⚓️-scope-name="--msg">
          <p class="bubble" data-⚓️-name="--msg">Did the anchors survive the RTL build?</p>
          <time class="stamp" data-⚓️-to="--msg" data-⚓️-side="after" data-⚓️-align-bottom>9:41</time>
        </li>
        <li class="out" data-⚓️-scope-name="--msg">
          <p class="bubble" data-⚓️-name="--msg">Every one. They're all logical sides.</p>
          <time class="stamp" data-⚓️-to="--msg" data-⚓️-side="before" data-⚓️-align-bottom>9:42</time>
          <span class="react" data-⚓️-to="--msg" data-⚓️-side="above" data-⚓️-align-trailing aria-label="Noor reacted">🔥</span>
        </li>
        <li class="in" data-⚓️-scope-name="--msg">
          <p class="bubble" data-⚓️-name="--msg">No translate hacks?</p>
          <time class="stamp" data-⚓️-to="--msg" data-⚓️-side="after" data-⚓️-align-bottom>9:42</time>
        </li>
        <li class="out" data-⚓️-scope-name="--msg">
          <p class="bubble" data-⚓️-name="--msg">Not one. Hit the button.</p>
          <time class="stamp" data-⚓️-to="--msg" data-⚓️-side="before" data-⚓️-align-bottom>9:43</time>
        </li>
      </ol>

      <form class="composer">
        <input type="text" aria-label="Message" placeholder="Write a message">
        <button type="submit" data-⚓️-name="--send" aria-label="Send">
          <svg viewBox="0 0 24 24" aria-hidden="true"><path d="M4 12h14M13 6l6 6-6 6"/></svg>
        </button>
        <span class="hint" data-⚓️-to="--send" data-⚓️-side="above" data-⚓️-align-trailing aria-hidden="true">Enter ↵ to send</span>
      </form>
    </section>

    <div id="menu" class="menu" popover="manual" data-⚓️-to="--more" data-⚓️-side="below" data-⚓️-align-trailing>
      <button type="button">Mute</button>
      <button type="button">Pin chat</button>
      <button type="button">Search</button>
    </div>
  </div>
</main>

/* Demo styling only. Every anchored thing is placed by data-⚓️-* attributes
   and every offset below is a logical margin, so none of it needs an RTL rule.
   The only :dir(rtl) rules are for the X-ray labels and the arrow icon. */
:root {
  color-scheme: light;
  --bg: oklch(97% 0.006 80);
  --ink: oklch(24% 0.02 270);
  --muted: oklch(52% 0.02 270);
  --line: oklch(89% 0.01 270);
  --accent: oklch(55% 0.2 275);
  --accent-soft: oklch(93% 0.04 275);
  --ease: cubic-bezier(0.25, 1, 0.5, 1);
  background: var(--bg);
  color: var(--ink);
  font: 400 1rem/1.5 system-ui, sans-serif;
}
body { margin: 0; }

.demo {
  max-width: 48rem;
  margin-inline: auto;
  padding: clamp(1rem, 4vw, 2.5rem);
  display: grid;
  gap: 1.25rem;
  overflow-x: clip; /* X-ray labels may poke past the edge on small screens */
}
.intro h1 { margin: 0 0 0.35rem; font-size: 1.5rem; font-weight: 650; letter-spacing: -0.01em; }
.intro p { margin: 0; color: var(--muted); max-width: 62ch; }
code { font: 0.88em ui-monospace, monospace; color: var(--accent); }

.bar { display: flex; justify-content: space-between; align-items: center; gap: 1rem; }
.flip {
  display: inline-flex;
  align-items: center;
  gap: 0.6rem;
  padding-block: 0.55rem;
  padding-inline: 0.7rem 1rem;
  border: 0;
  border-radius: 99px;
  background: var(--ink);
  color: oklch(98% 0 0);
  font: 600 0.9rem ui-monospace, monospace;
  cursor: pointer;
  transition: scale 0.15s var(--ease);
}
.flip:active { scale: 0.96; }
.flip-label { color: inherit; font: inherit; }
/* English copy in an RTL document: let each paragraph take its own
   direction so punctuation lands where it should. */
.intro p, .bubble, .composer input { unicode-bidi: plaintext; }
.flip:focus-visible { outline: 3px solid var(--accent); outline-offset: 3px; }
.flip-icon {
  display: grid;
  place-items: center;
  width: 1.6rem;
  aspect-ratio: 1;
  border-radius: 50%;
  background: var(--accent);
  font-size: 0.95rem;
  transition: rotate 0.4s var(--ease);
}
.flip[aria-pressed="true"] .flip-icon { rotate: 180deg; }
.xray-toggle { display: flex; gap: 0.4rem; align-items: center; color: var(--muted); font-size: 0.9rem; cursor: pointer; }
.xray-toggle input { accent-color: var(--accent); }

/* ---------- app shell ---------- */
.app {
  display: grid;
  grid-template-columns: 4.25rem 1fr;
  border: 1px solid var(--line);
  border-radius: 1.1rem;
  background: oklch(100% 0 0);
  box-shadow: 0 1.25rem 3rem -1.5rem oklch(30% 0.05 270 / 0.35);
}

.rail {
  padding-block: 1rem;
  border-inline-end: 1px solid var(--line);
  background: oklch(98.5% 0.004 270);
  border-start-start-radius: inherit;
  border-end-start-radius: inherit;
}
.rail ul { display: grid; justify-items: center; gap: 0.6rem; margin: 0; padding: 0; list-style: none; }
.rail a {
  display: grid;
  place-items: center;
  width: 2.6rem;
  aspect-ratio: 1;
  border-radius: 0.8rem;
  color: var(--muted);
  transition: background 0.2s, color 0.2s;
}
.rail a:hover, .rail a:focus-visible { background: var(--accent-soft); color: var(--accent); }
.rail a:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.rail a[aria-current] { background: var(--accent); color: oklch(99% 0 0); }
svg { width: 1.3rem; fill: none; stroke: currentColor; stroke-width: 1.8; stroke-linecap: round; stroke-linejoin: round; }

/* Tooltips: side="after" of their nav link, nub on the inline-start edge. */
.tip {
  z-index: 2;
  margin-inline-start: 0.7rem;
  padding: 0.3rem 0.6rem;
  border-radius: 0.45rem;
  background: var(--ink);
  color: oklch(98% 0 0);
  font-size: 0.8rem;
  font-weight: 500;
  white-space: nowrap;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.15s;
}
.tip::before {
  content: "";
  position: absolute;
  inset-block-start: 50%;
  inset-inline-start: -0.25rem;
  width: 0.5rem;
  aspect-ratio: 1;
  margin-block-start: -0.25rem;
  background: inherit;
  rotate: 45deg;
}
li:has(a:hover, a:focus-visible, a[aria-current]) > .tip { opacity: 1; }

/* ---------- conversation ---------- */
.chat { display: grid; grid-template-rows: auto 1fr auto; min-width: 0; }
.chat-head {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.8rem 1rem;
  border-block-end: 1px solid var(--line);
}
.avatar {
  display: grid;
  place-items: center;
  width: 2.4rem;
  aspect-ratio: 1;
  border-radius: 50%;
  background: linear-gradient(135deg, oklch(75% 0.14 30), oklch(62% 0.2 350));
  color: oklch(99% 0 0);
  font-weight: 700;
}
/* Presence dot: pinned to the avatar's trailing-bottom corner. */
.online {
  width: 0.8rem;
  aspect-ratio: 1;
  border-radius: 50%;
  background: oklch(72% 0.18 150);
  border: 2px solid oklch(100% 0 0);
  margin-inline-end: -0.1rem;
  margin-block-end: -0.1rem;
}
.who { display: grid; line-height: 1.2; }
.who small { color: var(--muted); }
.more {
  margin-inline-start: auto;
  width: 2.2rem;
  aspect-ratio: 1;
  border: 0;
  border-radius: 50%;
  background: transparent;
  color: var(--ink);
  font-size: 1.3rem;
  line-height: 1;
  cursor: pointer;
}
.more:hover, .more:focus-visible { background: var(--accent-soft); }

.thread {
  display: grid;
  gap: 1.1rem;
  align-content: start;
  margin: 0;
  padding: 1.25rem clamp(3rem, 12vw, 4.5rem) 2rem;
  list-style: none;
}
.thread li { display: grid; }
.bubble {
  max-width: 26ch;
  margin: 0;
  padding: 0.55rem 0.85rem;
  border-radius: 1.1rem;
  font-size: 0.95rem;
  line-height: 1.35;
}
.in .bubble { justify-self: start; background: oklch(95% 0.008 270); border-end-start-radius: 0.3rem; }
.out .bubble { justify-self: end; background: var(--accent); color: oklch(99% 0 0); border-end-end-radius: 0.3rem; }

.stamp { margin-inline: 0.45rem; color: var(--muted); font: 0.72rem ui-monospace, monospace; white-space: nowrap; }
/* Reaction: above the bubble's trailing corner, pulled down to overlap it. */
.react {
  margin-block-end: -0.75rem;
  margin-inline-end: -0.5rem;
  padding: 0.05rem 0.3rem;
  border-radius: 99px;
  background: oklch(100% 0 0);
  box-shadow: 0 0.15rem 0.5rem oklch(30% 0.05 270 / 0.25);
  font-size: 0.85rem;
}

.composer {
  display: flex;
  gap: 0.5rem;
  padding: 0.8rem 1rem;
  border-block-start: 1px solid var(--line);
}
.composer input {
  flex: 1;
  min-width: 0;
  padding: 0.55rem 0.9rem;
  border: 1px solid var(--line);
  border-radius: 99px;
  font: inherit;
  font-size: 0.95rem;
}
.composer input:focus-visible { outline: 2px solid var(--accent); outline-offset: 1px; }
.composer button {
  display: grid;
  place-items: center;
  width: 2.5rem;
  aspect-ratio: 1;
  border: 0;
  border-radius: 50%;
  background: var(--accent);
  color: oklch(99% 0 0);
  cursor: pointer;
}
.composer button:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
:dir(rtl) .composer svg { scale: -1 1; }
/* Hint: above the send button, flush with its trailing edge. */
.hint {
  margin-block-end: 0.5rem;
  padding: 0.25rem 0.55rem;
  border-radius: 0.4rem;
  background: oklch(92% 0.08 95);
  color: oklch(35% 0.06 80);
  font: 600 0.72rem ui-monospace, monospace;
  white-space: nowrap;
}

/* Menu popover: below the ⋯ button, flush with its trailing edge. */
.menu {
  display: none;
  margin-block-start: 0.4rem;
  padding: 0.35rem;
  border: 1px solid var(--line);
  border-radius: 0.75rem;
  background: oklch(100% 0 0);
  box-shadow: 0 0.75rem 2rem -0.5rem oklch(30% 0.05 270 / 0.35);
}
.menu:popover-open { display: grid; }
.menu button {
  padding-block: 0.4rem;
  padding-inline: 0.7rem 1.6rem;
  border: 0;
  border-radius: 0.45rem;
  background: none;
  color: var(--ink);
  font: inherit;
  font-size: 0.9rem;
  text-align: start;
  cursor: pointer;
}
.menu button:hover, .menu button:focus-visible { background: var(--accent-soft); }

/* ---------- mirror transition (view transition, set up in the script) ---------- */
.tip, .stamp, .react, .hint, .menu, .online, .avatar, .who, .bubble, .rail, .more,
.composer :is(input, button), .intro h1, .flip, .xray-toggle {
  view-transition-name: match-element;
}
::view-transition-group(*) { animation-duration: 0.55s; animation-timing-function: var(--ease); }

/* ---------- X-ray: outline anchors, label each target's side ---------- */
.demo:has(#xray:checked) [data-⚓️-name] { outline: 2px dashed oklch(65% 0.15 220); outline-offset: 2px; }
.demo:has(#xray:checked) [data-⚓️-to] { outline: 2px solid oklch(62% 0.22 330); outline-offset: 1px; }
.demo:has(#xray:checked) [data-⚓️-to]::after {
  position: absolute;
  inset-block-end: 100%;
  inset-inline-start: 0;
  margin-block-end: 0.2rem;
  padding: 0 0.3rem;
  border-radius: 0.25rem;
  background: oklch(62% 0.22 330);
  color: oklch(99% 0 0);
  font: 600 0.62rem/1.5 ui-monospace, monospace;
  white-space: nowrap;
  opacity: 1;
  z-index: 3;
}
.demo:has(#xray:checked) [data-⚓️-side="after"]::after  { content: "after → right"; }
.demo:has(#xray:checked) [data-⚓️-side="before"]::after { content: "before → left"; }
.demo:has(#xray:checked) [data-⚓️-side="after"]:dir(rtl)::after  { content: "after → left"; }
.demo:has(#xray:checked) [data-⚓️-side="before"]:dir(rtl)::after { content: "before → right"; }
.demo:has(#xray:checked) [data-⚓️-align-trailing]::after { content: attr(data-⚓️-side) " + trailing → right"; }
.demo:has(#xray:checked) [data-⚓️-align-trailing]:dir(rtl)::after { content: attr(data-⚓️-side) " + trailing → left"; }
.demo:has(#xray:checked) .online::after { content: "trailing → right"; }
.demo:has(#xray:checked) .online:dir(rtl)::after { content: "trailing → left"; }
.demo:has(#xray:checked) .tip { opacity: 1; }
.demo:has(#xray:checked) .stamp::after { inset-block-end: auto; inset-block-start: 100%; margin: 0.2rem 0 0; }

@media (prefers-reduced-motion: reduce) {
  .flip, .flip-icon, .tip, .rail a { transition: none; }
}

@media (width < 30rem) {
  .app { grid-template-columns: 3.4rem 1fr; }
  .rail a { width: 2.3rem; }
  .thread { padding-inline: 2.75rem; }
}

// State only: the button flips one attribute, dir, on <html>. Nothing is
// repositioned by script; the anchored sides are logical so they mirror.
// A view transition animates the swap where supported (skipped for
// reduced motion — then it's an instant mirror).
// It's set on the root element rather than the .app wrapper on purpose: the
// menu is a [popover], so its containing block is the viewport, and anchor()'s
// start/end keywords resolve against the containing block's direction.
const root = document.documentElement;
const flip = document.querySelector(".flip");
const value = document.querySelector(".flip-value");
const reduce = matchMedia("(prefers-reduced-motion: reduce)");

function mirror() {
  const next = root.dir === "rtl" ? "ltr" : "rtl";
  root.dir = next;
  value.textContent = next;
  flip.setAttribute("aria-pressed", String(next === "rtl"));
}

flip.addEventListener("click", () => {
  if (document.startViewTransition && !reduce.matches) document.startViewTransition(mirror);
  else mirror();
});

document.querySelector(".composer").addEventListener("submit", (e) => e.preventDefault());

// Show the menu open so its trailing alignment is visible from the start.
document.getElementById("menu").showPopover();