07幅が変わるたびに配置が着替えるカード

<main class="stage">
<div class="rh is-demo" id="rh" data-demo="1">
  <div class="rh__box" data-r="box">
    <div class="rh__cards">
      <div class="rh__card"><i></i><span><b></b><b></b></span></div>
      <div class="rh__card"><i></i><span><b></b><b></b></span></div>
      <div class="rh__card"><i></i><span><b></b><b></b></span></div>
    </div>
    <button class="rh__grip" data-r="grip" type="button" aria-label="サイズ変更つまみ"></button>
  </div>
  <p class="rh__meta"><span class="rh__tag">W</span> <b data-r="w">0</b> <span class="rh__tag">RANGE</span> <b data-r="range">STACK</b></p>
  <i class="rh__cursor" data-r="cursor"></i>
</div>
</main>

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

// 핵심: 상자 폭이 container-type: inline-size 의 기준이다. 폭 구간(150px, 250px)마다 카드 배치가 CSS 만으로 바뀐다.

@include stage($stage-yellow);

.rh {
  position: relative;
  box-sizing: border-box;
  width: min(100%, 440px);
  height: min(252px, calc(100vh - 2 * clamp(8px, 4vw, 24px)));
  color: $subject-ink;
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  user-select: none;
}
.rh b { font-weight: 800; font-variant-numeric: tabular-nums; }
.rh__tag { color: rgba($subject-ink, .72); letter-spacing: .5px; }
.rh__cursor {
  position: absolute;
  left: -10px;
  top: -10px;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: $subject-cream;
  box-shadow: 0 0 0 3px rgba($subject-ink, .55), $shadow-press;
  opacity: 0;
  pointer-events: none;
  z-index: 6;
}
.rh[data-demo] .rh__cursor { opacity: 1; }
.rh button:focus-visible { outline: 3px solid $subject-ink; outline-offset: 2px; }
@media (prefers-reduced-motion: reduce) {
  .rh__cursor { display: none; }
}

// JS 의 BREAK_A·BREAK_B 와 아래 두 @container 경계는 같은 숫자다.
.rh__box {
  position: absolute;
  left: 0;
  top: 0;
  box-sizing: border-box;
  height: calc(100% - 24px);
  container-type: inline-size;
  border-radius: $r-card;
  background: rgba($subject-ink, .12);
}
.rh__cards {
  position: absolute;
  inset: $sp-2 $sp-4 $sp-2 $sp-2;
  display: grid;
  grid-template-columns: 1fr;
  grid-auto-rows: 1fr;
  gap: $sp-2;
  overflow: hidden;
}
.rh__card {
  box-sizing: border-box;
  min-width: 0;
  min-height: 0;
  display: flex;
  flex-direction: row;
  align-items: center;
  gap: $sp-2;
  padding: $sp-2;
  overflow: hidden;
  border-radius: $r-sm;
  background: $subject-lilac;
}
.rh__card:nth-child(2) { background: $subject-mint; }
.rh__card:nth-child(3) { background: $subject-pink; }
.rh__card i {
  flex: none;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: rgba($subject-ink, .72);
}
.rh__card span { display: grid; gap: $sp-1; min-width: 0; flex: 1; }
.rh__card b { display: block; height: 6px; border-radius: $r-xs; background: rgba($subject-ink, .5); }
.rh__card b:last-child { width: 60%; }
@container (min-width: 150px) {
  .rh__cards { grid-template-columns: repeat(3, 1fr); grid-auto-rows: auto; }
  .rh__card { flex-direction: column; align-items: flex-start; justify-content: flex-start; }
  .rh__card span { width: 100%; flex: none; }
}
@container (min-width: 250px) {
  .rh__cards { grid-template-columns: 1fr 1fr; grid-template-rows: 1.2fr 1fr; }
  .rh__card:first-child { grid-column: 1 / -1; flex-direction: row; align-items: center; }
  .rh__card:first-child i { width: 40px; height: 40px; }
  .rh__card span { flex: 1; width: auto; }
}
.rh__grip {
  position: absolute;
  right: $sp-1;
  top: 50%;
  width: 8px;
  height: 56px;
  padding: 0;
  border: 0;
  border-radius: $r-pill;
  background: $subject-ink;
  transform: translateY(-50%);
  cursor: ew-resize;
  touch-action: none;
}
.rh__meta { position: absolute; left: 0; bottom: 0; margin: 0; }

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.rh {
  position: relative;
  box-sizing: border-box;
  width: min(100%, 440px);
  height: min(252px, 100vh - 2 * clamp(8px, 4vw, 24px));
  color: #17141a;
  font-size: 12px;
  line-height: 16px;
  font-weight: 600;
  user-select: none;
}

.rh b {
  font-weight: 800;
  font-variant-numeric: tabular-nums;
}

.rh__tag {
  color: rgba(23, 20, 26, 0.72);
  letter-spacing: 0.5px;
}

.rh__cursor {
  position: absolute;
  left: -10px;
  top: -10px;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: #fff7e6;
  box-shadow: 0 0 0 3px rgba(23, 20, 26, 0.55), 0 6px 12px rgba(23, 20, 26, 0.32);
  opacity: 0;
  pointer-events: none;
  z-index: 6;
}

.rh[data-demo] .rh__cursor {
  opacity: 1;
}

.rh button:focus-visible {
  outline: 3px solid #17141a;
  outline-offset: 2px;
}

@media (prefers-reduced-motion: reduce) {
  .rh__cursor {
    display: none;
  }
}
.rh__box {
  position: absolute;
  left: 0;
  top: 0;
  box-sizing: border-box;
  height: calc(100% - 24px);
  container-type: inline-size;
  border-radius: 16px;
  background: rgba(23, 20, 26, 0.12);
}

.rh__cards {
  position: absolute;
  inset: 8px 16px 8px 8px;
  display: grid;
  grid-template-columns: 1fr;
  grid-auto-rows: 1fr;
  gap: 8px;
  overflow: hidden;
}

.rh__card {
  box-sizing: border-box;
  min-width: 0;
  min-height: 0;
  display: flex;
  flex-direction: row;
  align-items: center;
  gap: 8px;
  padding: 8px;
  overflow: hidden;
  border-radius: 8px;
  background: #b9a0ff;
}

.rh__card:nth-child(2) {
  background: #4cd4a6;
}

.rh__card:nth-child(3) {
  background: #ff9ebb;
}

.rh__card i {
  flex: none;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background: rgba(23, 20, 26, 0.72);
}

.rh__card span {
  display: grid;
  gap: 4px;
  min-width: 0;
  flex: 1;
}

.rh__card b {
  display: block;
  height: 6px;
  border-radius: 4px;
  background: rgba(23, 20, 26, 0.5);
}

.rh__card b:last-child {
  width: 60%;
}

@container (min-width: 150px) {
  .rh__cards {
    grid-template-columns: repeat(3, 1fr);
    grid-auto-rows: auto;
  }
  .rh__card {
    flex-direction: column;
    align-items: flex-start;
    justify-content: flex-start;
  }
  .rh__card span {
    width: 100%;
    flex: none;
  }
}
@container (min-width: 250px) {
  .rh__cards {
    grid-template-columns: 1fr 1fr;
    grid-template-rows: 1.2fr 1fr;
  }
  .rh__card:first-child {
    grid-column: 1/-1;
    flex-direction: row;
    align-items: center;
  }
  .rh__card:first-child i {
    width: 40px;
    height: 40px;
  }
  .rh__card span {
    flex: 1;
    width: auto;
  }
}
.rh__grip {
  position: absolute;
  right: 4px;
  top: 50%;
  width: 8px;
  height: 56px;
  padding: 0;
  border: 0;
  border-radius: 999px;
  background: #17141a;
  transform: translateY(-50%);
  cursor: ew-resize;
  touch-action: none;
}

.rh__meta {
  position: absolute;
  left: 0;
  bottom: 0;
  margin: 0;
}

(function () {
    const root = document.getElementById("rh");
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let raf = 0;
    let t0 = -1;
    let last = -1;
    const offs = [];
    function q(sel) {
        return root.querySelector(sel);
    }
    function clamp(v, lo, hi) {
        return Math.max(lo, Math.min(hi, v));
    }
    function seg(t, a, b) {
        const c = clamp((t - a) / (b - a), 0, 1);
        return c * c * (3 - 2 * c);
    }
    function on(el, type, fn) {
        el.addEventListener(type, fn);
        offs.push(() => el.removeEventListener(type, fn));
    }
    function stopDemo() {
        demo = false;
        root.removeAttribute("data-demo");
        root.classList.remove("is-demo");
    }
    function pos(e) {
        const r = root.getBoundingClientRect();
        return { x: e.clientX - r.left, y: e.clientY - r.top };
    }
    function spring(x, v, to, k, c, dt) {
        const n = Math.max(1, Math.ceil(dt / 0.008));
        const h = dt / n;
        for (let i = 0; i < n; i += 1) {
            v += (-k * (x - to) - c * v) * h;
            x += v * h;
        }
        return [x, v];
    }
    function sync() {
        if (reduce) {
            snap();
            render();
        }
    }
    // 기법: 상자 너비 하나(cw)를 JS 가 끌고, 안쪽 배치는 CSS @container 가 너비 구간으로 바꾼다.
    // 구간 이름은 JS 가 같은 경계값(BREAK_A, BREAK_B)으로 읽어 화면 밑에 적는다.
    const BREAK_A = 150;
    const BREAK_B = 250;
    const RANGE_LABEL = ["STACK", "ROW", "GRID"];
    const MIN_W = 96;
    const FOLLOW = 16;
    const box = q("[data-r=box]");
    const grip = q("[data-r=grip]");
    const wEl = q("[data-r=w]");
    const rangeEl = q("[data-r=range]");
    const cursor = q("[data-r=cursor]");
    let cw = 0;
    let tw = 0;
    let px = 0;
    let py = 0;
    let gx = 0;
    let dragging = false;
    let ready = false;
    function maxW() { return root.clientWidth - 8; }
    function init() {
        if (ready)
            return;
        ready = true;
        tw = cw = root.clientWidth * 0.34;
    }
    function rangeOf(width) { return width < BREAK_A ? 0 : width < BREAK_B ? 1 : 2; }
    function userTakes() {
        stopDemo();
        dragging = false;
        init();
    }
    function script(now) {
        const W = root.clientWidth;
        const ph = now % 2000;
        const a = W * 0.34;
        const b = maxW();
        let x = a;
        if (ph >= 200 && ph < 760)
            x = a + (b - a) * seg(ph, 200, 760);
        else if (ph >= 760 && ph < 1100)
            x = b;
        else if (ph >= 1100 && ph < 1800)
            x = b + (a - b) * seg(ph, 1100, 1800);
        dragging = true;
        px = x - 4;
        py = root.clientHeight * 0.45;
        gx = 4;
    }
    function snap() {
        init();
        cw = tw;
    }
    function step(dt, now) {
        init();
        if (demo)
            script(now);
        if (dragging)
            tw = clamp(px + gx, MIN_W, maxW());
        cw += (tw - cw) * (1 - Math.exp(-FOLLOW * dt));
    }
    function render() {
        box.style.width = cw.toFixed(1) + "px";
        wEl.textContent = String(Math.round(cw));
        rangeEl.textContent = RANGE_LABEL[rangeOf(cw)];
        cursor.style.transform = "translate(" + px.toFixed(1) + "px," + py.toFixed(1) + "px)";
    }
    on(grip, "pointerdown", (e) => {
        userTakes();
        grip.setPointerCapture(e.pointerId);
        const p = pos(e);
        px = p.x;
        py = p.y;
        gx = cw - p.x;
        dragging = true;
    });
    on(grip, "pointermove", (e) => {
        if (!dragging)
            return;
        px = pos(e).x;
        tw = clamp(px + gx, MIN_W, maxW());
        sync();
    });
    on(grip, "pointerup", () => { dragging = false; });
    on(grip, "pointercancel", () => { dragging = false; });
    on(grip, "keydown", (e) => {
        if (e.key !== "ArrowLeft" && e.key !== "ArrowRight")
            return;
        e.preventDefault();
        userTakes();
        tw = clamp(tw + (e.key === "ArrowRight" ? 16 : -16), MIN_W, maxW());
        sync();
    });
    function frame(ts) {
        if (t0 < 0) {
            t0 = ts;
            last = ts;
        }
        const dt = Math.min(0.05, (ts - last) / 1000);
        last = ts;
        step(dt, ts - t0);
        render();
        raf = requestAnimationFrame(frame);
    }
    if (reduce) {
        stopDemo();
        snap();
        render();
    }
    else {
        raf = requestAnimationFrame(frame);
    }
    return () => {
        cancelAnimationFrame(raf);
        offs.forEach((f) => f());
    };
})();

// ContainerReflowReadout - vanilla 판(07-rh-container-reflow-readout) 의 React 포트. 같은 계산을 useEffect 안에서 돌린다.
import { useEffect, useRef } from "react";
import styles from "./ContainerReflowReadout.module.scss";

export default function ContainerReflowReadout() {
  const rootRef = useRef<HTMLDivElement | null>(null);

  useEffect(() => {
    const rootEl = rootRef.current;
    if (!rootEl) return;
    const root: HTMLElement = rootEl;
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let raf = 0;
    let t0 = -1;
    let last = -1;
    const offs: Array<() => void> = [];

    function q<T extends Element>(sel: string): T {
      return root.querySelector(sel) as T;
    }
    function clamp(v: number, lo: number, hi: number): number {
      return Math.max(lo, Math.min(hi, v));
    }
    function seg(t: number, a: number, b: number): number {
      const c = clamp((t - a) / (b - a), 0, 1);
      return c * c * (3 - 2 * c);
    }
    function on(el: EventTarget, type: string, fn: (e: any) => void): void {
      el.addEventListener(type, fn);
      offs.push(() => el.removeEventListener(type, fn));
    }
    function stopDemo(): void {
      demo = false;
      root.removeAttribute("data-demo");
      root.classList.remove("is-demo");
    }
    function pos(e: PointerEvent): { x: number; y: number } {
      const r = root.getBoundingClientRect();
      return { x: e.clientX - r.left, y: e.clientY - r.top };
    }
    function spring(x: number, v: number, to: number, k: number, c: number, dt: number): number[] {
      const n = Math.max(1, Math.ceil(dt / 0.008));
      const h = dt / n;
      for (let i = 0; i < n; i += 1) {
        v += (-k * (x - to) - c * v) * h;
        x += v * h;
      }
      return [x, v];
    }
    function sync(): void {
      if (reduce) {
        snap();
        render();
      }
    }

    // 기법: 상자 너비 하나(cw)를 JS 가 끌고, 안쪽 배치는 CSS @container 가 너비 구간으로 바꾼다.
    // 구간 이름은 JS 가 같은 경계값(BREAK_A, BREAK_B)으로 읽어 화면 밑에 적는다.
    const BREAK_A = 150;
    const BREAK_B = 250;
    const RANGE_LABEL = ["STACK", "ROW", "GRID"];
    const MIN_W = 96;
    const FOLLOW = 16;
    const box = q<HTMLElement>("[data-r=box]");
    const grip = q<HTMLElement>("[data-r=grip]");
    const wEl = q<HTMLElement>("[data-r=w]");
    const rangeEl = q<HTMLElement>("[data-r=range]");
    const cursor = q<HTMLElement>("[data-r=cursor]");
    let cw = 0;
    let tw = 0;
    let px = 0;
    let py = 0;
    let gx = 0;
    let dragging = false;
    let ready = false;

    function maxW(): number { return root.clientWidth - 8; }

    function init(): void {
      if (ready) return;
      ready = true;
      tw = cw = root.clientWidth * 0.34;
    }

    function rangeOf(width: number): number { return width < BREAK_A ? 0 : width < BREAK_B ? 1 : 2; }

    function userTakes(): void {
      stopDemo();
      dragging = false;
      init();
    }

    function script(now: number): void {
      const W = root.clientWidth;
      const ph = now % 2000;
      const a = W * 0.34;
      const b = maxW();
      let x = a;
      if (ph >= 200 && ph < 760) x = a + (b - a) * seg(ph, 200, 760);
      else if (ph >= 760 && ph < 1100) x = b;
      else if (ph >= 1100 && ph < 1800) x = b + (a - b) * seg(ph, 1100, 1800);
      dragging = true;
      px = x - 4;
      py = root.clientHeight * 0.45;
      gx = 4;
    }

    function snap(): void {
      init();
      cw = tw;
    }

    function step(dt: number, now: number): void {
      init();
      if (demo) script(now);
      if (dragging) tw = clamp(px + gx, MIN_W, maxW());
      cw += (tw - cw) * (1 - Math.exp(-FOLLOW * dt));
    }

    function render(): void {
      box.style.width = cw.toFixed(1) + "px";
      wEl.textContent = String(Math.round(cw));
      rangeEl.textContent = RANGE_LABEL[rangeOf(cw)];
      cursor.style.transform = "translate(" + px.toFixed(1) + "px," + py.toFixed(1) + "px)";
    }

    on(grip, "pointerdown", (e: PointerEvent) => {
      userTakes();
      grip.setPointerCapture(e.pointerId);
      const p = pos(e);
      px = p.x;
      py = p.y;
      gx = cw - p.x;
      dragging = true;
    });
    on(grip, "pointermove", (e: PointerEvent) => {
      if (!dragging) return;
      px = pos(e).x;
      tw = clamp(px + gx, MIN_W, maxW());
      sync();
    });
    on(grip, "pointerup", () => { dragging = false; });
    on(grip, "pointercancel", () => { dragging = false; });
    on(grip, "keydown", (e: KeyboardEvent) => {
      if (e.key !== "ArrowLeft" && e.key !== "ArrowRight") return;
      e.preventDefault();
      userTakes();
      tw = clamp(tw + (e.key === "ArrowRight" ? 16 : -16), MIN_W, maxW());
      sync();
    });

    function frame(ts: number): void {
      if (t0 < 0) {
        t0 = ts;
        last = ts;
      }
      const dt = Math.min(0.05, (ts - last) / 1000);
      last = ts;
      step(dt, ts - t0);
      render();
      raf = requestAnimationFrame(frame);
    }
    if (reduce) {
      stopDemo();
      snap();
      render();
    } else {
      raf = requestAnimationFrame(frame);
    }
    return () => {
      cancelAnimationFrame(raf);
      offs.forEach((f) => f());
    };

  }, []);

  return (
    <main className={styles["stage"]}>
      <div ref={rootRef} className={styles["rh"] + " is-demo"} data-demo="1">
        <div className={styles["rh__box"]} data-r="box">
          <div className={styles["rh__cards"]}>
            <div className={styles["rh__card"]}><i></i><span><b></b><b></b></span></div>
            <div className={styles["rh__card"]}><i></i><span><b></b><b></b></span></div>
            <div className={styles["rh__card"]}><i></i><span><b></b><b></b></span></div>
          </div>
          <button className={styles["rh__grip"]} data-r="grip" type="button" aria-label="크기 조절 손잡이"></button>
        </div>
        <p className={styles["rh__meta"]}><span className={styles["rh__tag"]}>W</span> <b data-r="w">0</b> <span className={styles["rh__tag"]}>RANGE</span> <b data-r="range">STACK</b></p>
        <i className={styles["rh__cursor"]} data-r="cursor"></i>
      </div>
    </main>
  );
}