05要素群ごとに異なる減速値を与えるクラス指定遷移

<main class="stage">
<div class="ce is-demo" id="ce">
  <div class="ce__hero" id="ceHero"></div>
  <button type="button" class="ce__btn" id="ceBtn" aria-label="配置トランジション — 背景はゆっくり、ボタンは速く">トランジション</button>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;
$easing: $ease-spring;
$color: $subject-blue-light;

@include stage($stage-ink);

.ce { position: relative; width: min(100%, 300px); height: 180px; display: flex; flex-direction: column; gap: $sp-3; justify-content: center; }

.ce__hero {
  view-transition-name: ce-hero;
  view-transition-class: vt-slow;
  width: 60%; height: 88px; border-radius: $r-card; background: $subject-blue-deep;
}
.is-wide .ce__hero { width: 100%; background: $color; }

.ce__btn {
  view-transition-name: ce-btn;
  view-transition-class: vt-fast;
  align-self: flex-start; border: none; border-radius: $r-pill; cursor: pointer;
  background: $subject-cream; color: $subject-ink; font: 700 12px/1 -apple-system, sans-serif;
  padding: $sp-2 $sp-4;
}
.is-wide .ce__btn { align-self: flex-end; }
.ce__btn:focus-visible { outline: 2px solid $subject-cream; outline-offset: 2px; }

// 실사용 원리: view-transition-class 값(vt-slow·vt-fast)을 요소마다 다르게 달아 두면
// 이름은 제각각이어도 ::view-transition-group(.클래스) 로 한 번에 묶어 지속시간을 나눌 수 있다 —
// 배경은 느리게(감속 값 큼) 버튼은 빠르게(감속 값 작음) 같은 트리거에서 서로 다른 속도로 움직인다.
::view-transition-group(.vt-slow) {
  animation-duration: $duration / 2.2;
  animation-timing-function: $easing;
}
::view-transition-group(.vt-fast) {
  animation-duration: $dur-quick;
  animation-timing-function: $ease-pop;
}

@media (max-width: 340px) {
  .ce { height: 150px; gap: $sp-2; }
  .ce__hero { height: 70px; }
  .ce__btn { padding: $sp-1 $sp-3; font-size: 11px; }
}

@media (prefers-reduced-motion: reduce) {
  ::view-transition-group(*),
  ::view-transition-old(*),
  ::view-transition-new(*) { animation: none !important; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.ce {
  position: relative;
  width: min(100%, 300px);
  height: 180px;
  display: flex;
  flex-direction: column;
  gap: 12px;
  justify-content: center;
}

.ce__hero {
  view-transition-name: ce-hero;
  view-transition-class: vt-slow;
  width: 60%;
  height: 88px;
  border-radius: 16px;
  background: #0a4fe8;
}

.is-wide .ce__hero {
  width: 100%;
  background: #5b8cf8;
}

.ce__btn {
  view-transition-name: ce-btn;
  view-transition-class: vt-fast;
  align-self: flex-start;
  border: none;
  border-radius: 999px;
  cursor: pointer;
  background: #fff7e6;
  color: #17141a;
  font: 700 12px/1 -apple-system, sans-serif;
  padding: 8px 16px;
}

.is-wide .ce__btn {
  align-self: flex-end;
}

.ce__btn:focus-visible {
  outline: 2px solid #fff7e6;
  outline-offset: 2px;
}

::view-transition-group(.vt-slow) {
  animation-duration: 0.9090909091s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
}

::view-transition-group(.vt-fast) {
  animation-duration: 220ms;
  animation-timing-function: cubic-bezier(0.2, 1.4, 0.4, 1);
}

@media (max-width: 340px) {
  .ce {
    height: 150px;
    gap: 8px;
  }
  .ce__hero {
    height: 70px;
  }
  .ce__btn {
    padding: 4px 12px;
    font-size: 11px;
  }
}
@media (prefers-reduced-motion: reduce) {
  ::view-transition-group(*),
  ::view-transition-old(*),
  ::view-transition-new(*) {
    animation: none !important;
  }
}

(function () {
  var SUPPORTS_VT = 'startViewTransition' in document;

  var root = document.getElementById('ce');
  var hero = document.getElementById('ceHero');
  var btn = document.getElementById('ceBtn');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  var wide = false;
  var isDemo = true;

  function human() {
    if (isDemo) { root.classList.remove('is-demo'); isDemo = false; }
  }

  function render() {
    root.classList.toggle('is-wide', wide);
  }

  function change(fn) {
    if (SUPPORTS_VT) { document.startViewTransition(fn); }
    else { fn(); }
  }

  function toggle() {
    wide = !wide;
    change(render);
  }

  btn.addEventListener('click', function () { human(); toggle(); });
  root.addEventListener('keydown', function (e) {
    if (e.key === 'Enter' || e.key === ' ') { human(); e.preventDefault(); toggle(); }
  });

  var HOLD_MS = 1000;
  function loop() {
    if (!isDemo) return;
    toggle();
    window.setTimeout(loop, HOLD_MS);
  }

  if (!reduce) {
    window.setTimeout(loop, HOLD_MS);
  } else {
    root.classList.remove('is-demo');
  }
})();

// ClassCustomEasing — vanilla 판(run/401/demo/05-view-transition-class-custom-easing/index.html) 의 React 포트.
// 계산 겹 없음(브리프 지정) — view-transition-class 로 요소군마다 다른 이징을 묶어 지정한다.
import { useEffect, useRef } from "react";
import styles from "./ClassCustomEasing.module.scss";

type Box<T> = { current: T };

const HOLD_MS = 1000;

export default function ClassCustomEasing() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement>;
  const btnRef = useRef(null) as unknown as Box<HTMLButtonElement>;
  const timerRef = useRef(0) as unknown as Box<number>;

  useEffect(() => {
    const SUPPORTS_VT = "startViewTransition" in document;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let isDemo = true;
    let wide = false;

    function human() {
      if (isDemo) { rootRef.current?.classList.remove(styles.isDemo); isDemo = false; }
    }

    function render() {
      rootRef.current?.classList.toggle(styles.isWide, wide);
    }

    function change(fn: () => void) {
      if (SUPPORTS_VT) { document.startViewTransition(fn); }
      else { fn(); }
    }

    function toggle() {
      wide = !wide;
      change(render);
    }

    function onClick() { human(); toggle(); }
    function onKeydown(e: KeyboardEvent) {
      if (e.key === "Enter" || e.key === " ") { human(); e.preventDefault(); toggle(); }
    }

    btnRef.current?.addEventListener("click", onClick);
    rootRef.current?.addEventListener("keydown", onKeydown);

    function loop() {
      if (!isDemo) return;
      toggle();
      timerRef.current = window.setTimeout(loop, HOLD_MS);
    }

    if (!reduce) {
      timerRef.current = window.setTimeout(loop, HOLD_MS);
    } else {
      rootRef.current?.classList.remove(styles.isDemo);
    }

    return () => {
      window.clearTimeout(timerRef.current);
      btnRef.current?.removeEventListener("click", onClick);
      rootRef.current?.removeEventListener("keydown", onKeydown);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={styles.ce + " " + styles.isDemo} ref={rootRef}>
        <div className={styles.hero} />
        <button type="button" className={styles.btn} ref={btnRef} aria-label="배치 전환 — 배경은 느리게 버튼은 빠르게">전환</button>
      </div>
    </main>
  );
}