07Panel whose height stretches along as you move between tabs

<main class="stage">
  <section class="th is-demo" id="th">
    <div class="th__tabs" role="tablist" aria-label="Pricing tabs">
      <button class="th__tab" type="button" role="tab" id="th-t1" aria-controls="th-p1" aria-selected="true">Free</button>
      <button class="th__tab" type="button" role="tab" id="th-t2" aria-controls="th-p2" aria-selected="false" tabindex="-1">Pro</button>
      <button class="th__tab" type="button" role="tab" id="th-t3" aria-controls="th-p3" aria-selected="false" tabindex="-1">Team</button>
    </div>

    <div class="th__panels">
      <div class="th__panel is-open" role="tabpanel" id="th-p1" aria-labelledby="th-t1">
        <div class="th__clip">
          <div class="th__body">
            <p class="th__price">$0</p>
            <p class="th__desc">Enough when it is just you.</p>
          </div>
        </div>
      </div>
      <div class="th__panel" role="tabpanel" id="th-p2" aria-labelledby="th-t2" aria-hidden="true">
        <div class="th__clip">
          <div class="th__body">
            <p class="th__price">$9 / month</p>
            <p class="th__desc">Keep an unlimited history, use every export format, and roll back anything you changed in the last 30 days. Replies arrive within a day.</p>
          </div>
        </div>
      </div>
      <div class="th__panel" role="tabpanel" id="th-p3" aria-labelledby="th-t3" aria-hidden="true">
        <div class="th__clip">
          <div class="th__body">
            <p class="th__price">$24 / month</p>
            <p class="th__desc">Up to five people share one workspace.</p>
          </div>
        </div>
      </div>
    </div>
  </section>
</main>

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

// 탭 높이 모프 — 패널을 grid-template-rows 의 0fr 과 1fr 사이에서 보간해
// 내용 높이를 미리 모르고도 부드럽게 늘린다. 내용 교체는 컷, 높이만 보간한다.
$duration: $dur-base;
$easing: $ease-spring;
$color: $subject-cream;

@include stage($stage-orange);

$ink-soft: rgba(23, 20, 26, .68);
$ink-track: rgba(23, 20, 26, .09);

.th {
  box-sizing: border-box;
  display: grid;
  gap: $sp-2;
  width: min(300px, 92vw);
  padding: $sp-3;
  border-radius: $r-card;
  background: $color;
  color: $subject-ink;
  box-shadow: $shadow-raised;
}
.th * { box-sizing: border-box; }

// ── 탭 줄: 인디케이터를 고정 px 로 옮기지 않는다. 칸은 1fr 3등분, 표시는 배경으로 ──
.th__tabs {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: $sp-1;
  padding: $sp-1;
  border-radius: $r-pill;
  background: $ink-track;
}
.th__tab {
  margin: 0;
  padding: $sp-2 0;
  border: 0;
  border-radius: $r-pill;
  background: transparent;
  color: $ink-soft;
  font-family: inherit;
  font-size: 13px;
  font-weight: 700;
  line-height: 1;
  cursor: pointer;
  transition: background-color $duration $easing, color $duration $easing;
}
.th__tab:focus-visible { outline: 2px solid $subject-ink; outline-offset: 2px; }
.th__tab[aria-selected="true"] { background: $subject-ink; color: $color; }

// ── 패널: 0fr ↔ 1fr 보간 ──
// 0fr 칸의 자식에 min-height: 0 과 overflow: hidden 이 둘 다 있어야 실제로 접힌다.
// 접히는 칸에 세로 패딩을 주면 0fr 에서도 그만큼 남으므로 패딩은 안쪽 래퍼에 둔다.
.th__panel {
  display: grid;
  grid-template-rows: 0fr;
  transition: grid-template-rows $duration $easing;
}
.th__panel.is-open { grid-template-rows: 1fr; }
.th__clip { min-height: 0; overflow: hidden; }
.th__body {
  padding: $sp-2 0 0;
  opacity: 0;
  transition: opacity $duration steps(1, end);
}
// 펼침은 바로 보이고, 접힘은 높이가 다 줄어든 뒤 한 프레임에 컷 — 크로스페이드가 생기지 않는다
.th__panel.is-open .th__body { opacity: 1; transition-duration: 0s; }

.th__price {
  margin: 0;
  font-size: 22px;
  font-weight: 800;
  line-height: 1.1;
}
.th__desc {
  margin: $sp-1 0 0;
  color: $ink-soft;
  font-size: 12px;
  font-weight: 500;
  line-height: 1.5;
}

// ── 격자 미리보기 전용 2초 루프 ──
// 높이는 이징으로 보간하고(아래 th-row-*), 글자와 탭 표시는 steps(1, end) 컷으로 갈아 끼운다.
@keyframes th-row-1 {
  0%, 20% { grid-template-rows: 1fr; }
  28%, 82% { grid-template-rows: 0fr; }
  90%, 100% { grid-template-rows: 1fr; }
}
@keyframes th-row-2 {
  0%, 20% { grid-template-rows: 0fr; }
  28%, 48% { grid-template-rows: 1fr; }
  56%, 100% { grid-template-rows: 0fr; }
}
@keyframes th-row-3 {
  0%, 48% { grid-template-rows: 0fr; }
  56%, 74% { grid-template-rows: 1fr; }
  82%, 100% { grid-template-rows: 0fr; }
}
@keyframes th-body-1 {
  0% { opacity: 1; }
  28% { opacity: 0; }
  82%, 100% { opacity: 1; }
}
@keyframes th-body-2 {
  0% { opacity: 0; }
  20% { opacity: 1; }
  56%, 100% { opacity: 0; }
}
@keyframes th-body-3 {
  0% { opacity: 0; }
  48% { opacity: 1; }
  82%, 100% { opacity: 0; }
}
@keyframes th-tab-1 {
  0% { background-color: $subject-ink; color: $color; }
  20% { background-color: transparent; color: $ink-soft; }
  82%, 100% { background-color: $subject-ink; color: $color; }
}
@keyframes th-tab-2 {
  0% { background-color: transparent; color: $ink-soft; }
  20% { background-color: $subject-ink; color: $color; }
  48%, 100% { background-color: transparent; color: $ink-soft; }
}
@keyframes th-tab-3 {
  0% { background-color: transparent; color: $ink-soft; }
  48% { background-color: $subject-ink; color: $color; }
  82%, 100% { background-color: transparent; color: $ink-soft; }
}

.th.is-demo {
  .th__panel:nth-child(1) { animation-name: th-row-1; }
  .th__panel:nth-child(2) { animation-name: th-row-2; }
  .th__panel:nth-child(3) { animation-name: th-row-3; }
  .th__panel {
    animation-duration: $dur-loop;
    animation-timing-function: $easing;
    animation-iteration-count: infinite;
    animation-fill-mode: backwards;
  }
  .th__panel:nth-child(1) .th__body { animation-name: th-body-1; }
  .th__panel:nth-child(2) .th__body { animation-name: th-body-2; }
  .th__panel:nth-child(3) .th__body { animation-name: th-body-3; }
  .th__tab:nth-child(1) { animation-name: th-tab-1; }
  .th__tab:nth-child(2) { animation-name: th-tab-2; }
  .th__tab:nth-child(3) { animation-name: th-tab-3; }
  .th__body,
  .th__tab {
    animation-duration: $dur-loop;
    animation-timing-function: steps(1, end);
    animation-iteration-count: infinite;
    animation-fill-mode: backwards;
  }
}

@media (max-width: 340px) {
  .th { gap: $sp-1; width: min(292px, 96vw); padding: $sp-2; }
  .th__tabs { gap: 0; }
  .th__tab { padding: $sp-1 0; font-size: 11px; }
  .th__body { padding: $sp-1 0 0; }
  .th__price { font-size: 17px; }
  .th__desc { margin: 0; font-size: 10px; }
}

@media (prefers-reduced-motion: reduce) {
  .th.is-demo .th__panel,
  .th.is-demo .th__body,
  .th.is-demo .th__tab { animation: none !important; transition: none !important; }
  // 움직임만 끄고 첫 탭이 펼쳐진 결과는 그대로 남긴다
  .th.is-demo .th__panel:nth-child(1) { grid-template-rows: 1fr !important; }
  .th.is-demo .th__panel:nth-child(1) .th__body { opacity: 1 !important; }
  .th.is-demo .th__tab:nth-child(1) { background-color: $subject-ink !important; color: $color !important; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.th {
  box-sizing: border-box;
  display: grid;
  gap: 8px;
  width: min(300px, 92vw);
  padding: 12px;
  border-radius: 16px;
  background: #fff7e6;
  color: #17141a;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.th * {
  box-sizing: border-box;
}

.th__tabs {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 4px;
  padding: 4px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.09);
}

.th__tab {
  margin: 0;
  padding: 8px 0;
  border: 0;
  border-radius: 999px;
  background: transparent;
  color: rgba(23, 20, 26, 0.68);
  font-family: inherit;
  font-size: 13px;
  font-weight: 700;
  line-height: 1;
  cursor: pointer;
  transition: background-color 300ms cubic-bezier(0.2, 0.8, 0.2, 1), color 300ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

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

.th__tab[aria-selected=true] {
  background: #17141a;
  color: #fff7e6;
}

.th__panel {
  display: grid;
  grid-template-rows: 0fr;
  transition: grid-template-rows 300ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.th__panel.is-open {
  grid-template-rows: 1fr;
}

.th__clip {
  min-height: 0;
  overflow: hidden;
}

.th__body {
  padding: 8px 0 0;
  opacity: 0;
  transition: opacity 300ms steps(1, end);
}

.th__panel.is-open .th__body {
  opacity: 1;
  transition-duration: 0s;
}

.th__price {
  margin: 0;
  font-size: 22px;
  font-weight: 800;
  line-height: 1.1;
}

.th__desc {
  margin: 4px 0 0;
  color: rgba(23, 20, 26, 0.68);
  font-size: 12px;
  font-weight: 500;
  line-height: 1.5;
}

@keyframes th-row-1 {
  0%, 20% {
    grid-template-rows: 1fr;
  }
  28%, 82% {
    grid-template-rows: 0fr;
  }
  90%, 100% {
    grid-template-rows: 1fr;
  }
}
@keyframes th-row-2 {
  0%, 20% {
    grid-template-rows: 0fr;
  }
  28%, 48% {
    grid-template-rows: 1fr;
  }
  56%, 100% {
    grid-template-rows: 0fr;
  }
}
@keyframes th-row-3 {
  0%, 48% {
    grid-template-rows: 0fr;
  }
  56%, 74% {
    grid-template-rows: 1fr;
  }
  82%, 100% {
    grid-template-rows: 0fr;
  }
}
@keyframes th-body-1 {
  0% {
    opacity: 1;
  }
  28% {
    opacity: 0;
  }
  82%, 100% {
    opacity: 1;
  }
}
@keyframes th-body-2 {
  0% {
    opacity: 0;
  }
  20% {
    opacity: 1;
  }
  56%, 100% {
    opacity: 0;
  }
}
@keyframes th-body-3 {
  0% {
    opacity: 0;
  }
  48% {
    opacity: 1;
  }
  82%, 100% {
    opacity: 0;
  }
}
@keyframes th-tab-1 {
  0% {
    background-color: #17141a;
    color: #fff7e6;
  }
  20% {
    background-color: transparent;
    color: rgba(23, 20, 26, 0.68);
  }
  82%, 100% {
    background-color: #17141a;
    color: #fff7e6;
  }
}
@keyframes th-tab-2 {
  0% {
    background-color: transparent;
    color: rgba(23, 20, 26, 0.68);
  }
  20% {
    background-color: #17141a;
    color: #fff7e6;
  }
  48%, 100% {
    background-color: transparent;
    color: rgba(23, 20, 26, 0.68);
  }
}
@keyframes th-tab-3 {
  0% {
    background-color: transparent;
    color: rgba(23, 20, 26, 0.68);
  }
  48% {
    background-color: #17141a;
    color: #fff7e6;
  }
  82%, 100% {
    background-color: transparent;
    color: rgba(23, 20, 26, 0.68);
  }
}
.th.is-demo .th__panel:nth-child(1) {
  animation-name: th-row-1;
}
.th.is-demo .th__panel:nth-child(2) {
  animation-name: th-row-2;
}
.th.is-demo .th__panel:nth-child(3) {
  animation-name: th-row-3;
}
.th.is-demo .th__panel {
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
  animation-fill-mode: backwards;
}
.th.is-demo .th__panel:nth-child(1) .th__body {
  animation-name: th-body-1;
}
.th.is-demo .th__panel:nth-child(2) .th__body {
  animation-name: th-body-2;
}
.th.is-demo .th__panel:nth-child(3) .th__body {
  animation-name: th-body-3;
}
.th.is-demo .th__tab:nth-child(1) {
  animation-name: th-tab-1;
}
.th.is-demo .th__tab:nth-child(2) {
  animation-name: th-tab-2;
}
.th.is-demo .th__tab:nth-child(3) {
  animation-name: th-tab-3;
}
.th.is-demo .th__body,
.th.is-demo .th__tab {
  animation-duration: 2s;
  animation-timing-function: steps(1, end);
  animation-iteration-count: infinite;
  animation-fill-mode: backwards;
}

@media (max-width: 340px) {
  .th {
    gap: 4px;
    width: min(292px, 96vw);
    padding: 8px;
  }
  .th__tabs {
    gap: 0;
  }
  .th__tab {
    padding: 4px 0;
    font-size: 11px;
  }
  .th__body {
    padding: 4px 0 0;
  }
  .th__price {
    font-size: 17px;
  }
  .th__desc {
    margin: 0;
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .th.is-demo .th__panel,
  .th.is-demo .th__body,
  .th.is-demo .th__tab {
    animation: none !important;
    transition: none !important;
  }
  .th.is-demo .th__panel:nth-child(1) {
    grid-template-rows: 1fr !important;
  }
  .th.is-demo .th__panel:nth-child(1) .th__body {
    opacity: 1 !important;
  }
  .th.is-demo .th__tab:nth-child(1) {
    background-color: #17141a !important;
    color: #fff7e6 !important;
  }
}

// 탭 높이 모프: 고른 탭은 aria-selected 가 들고, 패널은 0fr ↔ 1fr 사이에서 높이가 보간된다.
var th = document.getElementById('th');
var thTabs = [].slice.call(th.querySelectorAll('.th__tab'));
function thSelect(i) {
  th.classList.remove('is-demo');
  thTabs.forEach(function (t, n) {
    var on = n === i;
    t.setAttribute('aria-selected', on ? 'true' : 'false');
    t.tabIndex = on ? 0 : -1;
    var p = document.getElementById(t.getAttribute('aria-controls'));
    p.classList.toggle('is-open', on);
    p.setAttribute('aria-hidden', on ? 'false' : 'true');
  });
}
thTabs.forEach(function (t, i) {
  t.addEventListener('click', function () { thSelect(i); });
  t.addEventListener('keydown', function (e) {
    var d = e.key === 'ArrowRight' ? 1 : e.key === 'ArrowLeft' ? -1 : 0;
    if (!d) return;
    e.preventDefault();
    var n = (i + d + thTabs.length) % thTabs.length;
    thSelect(n);
    thTabs[n].focus({ preventScroll: true });
  });
});

import { useState, useRef } from "react";
import type { CSSProperties } from "react";
import styles from "./TabHeightMorph.module.scss";

export type TabHeightMorphItem = { tab: string; price: string; desc: string };

export type TabHeightMorphProps = {
  /** 탭 라벨과 그 안의 내용. 설명 길이가 제각각이어도 높이가 따라 늘어난다 */
  items?: TabHeightMorphItem[];
  groupLabel?: string;
  /** 격자 미리보기용 2초 자동 루프. 사람이 손대면 꺼진다 */
  demo?: boolean;
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
// ambient 가 얇아 KeyboardEvent·HTMLElement 를 못 쓴다 — 필요한 꼴만 로컬 타입으로 선언
type KeyEvt = { key: string; preventDefault(): void };
type Focusable = { focus(o: { preventScroll: boolean }): void };
type Box<T> = { current: T };

const DEFAULT_ITEMS: TabHeightMorphItem[] = [
  { tab: "Free", price: "$0", desc: "Enough when it is just you." },
  {
    tab: "Pro",
    price: "$9 / month",
    desc:
      "Keep an unlimited history, use every export format, and roll back anything you changed in the last 30 days. Replies arrive within a day.",
  },
  { tab: "Team", price: "$24 / month", desc: "Up to five people share one workspace." },
];

let seq = 0;

export default function TabHeightMorph({
  items = DEFAULT_ITEMS,
  groupLabel = "Pricing tabs",
  demo = true,
  duration = 300,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#fff7e6",
}: TabHeightMorphProps) {
  const [current, setCurrent] = useState(0);
  const [live, setLive] = useState(demo);
  const [uid] = useState<string>(() => "tab-height-morph-" + String(++seq));
  // useRef 는 { current: T | null } 이라 배열로 쓸 땐 단언이 필요하다
  const tabRefs = useRef<(Focusable | null)[]>([]) as Box<(Focusable | null)[]>;

  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  function select(i: number) {
    setLive(false);
    setCurrent(i);
  }

  function onKeyDown(e: KeyEvt, i: number) {
    const step = e.key === "ArrowRight" ? 1 : e.key === "ArrowLeft" ? -1 : 0;
    if (step === 0) return;
    e.preventDefault();
    const next = (i + step + items.length) % items.length;
    select(next);
    const el = tabRefs.current[next];
    // iframe 안에서 무가드 focus 는 부모 페이지를 끌어당긴다
    if (el) el.focus({ preventScroll: true });
  }

  const cls = [styles.th, live ? styles.isDemo : ""].filter(Boolean).join(" ");

  return (
    <section className={cls} style={vars}>
      <div className={styles.tabs} role="tablist" aria-label={groupLabel}>
        {items.map((it, i) => (
          <button
            key={it.tab}
            className={styles.tab}
            type="button"
            role="tab"
            id={`${uid}-t${i}`}
            aria-controls={`${uid}-p${i}`}
            aria-selected={i === current}
            tabIndex={i === current ? 0 : -1}
            ref={(el: Focusable | null) => {
              tabRefs.current[i] = el;
            }}
            onClick={() => select(i)}
            onKeyDown={(e: KeyEvt) => onKeyDown(e, i)}
          >
            {it.tab}
          </button>
        ))}
      </div>

      <div className={styles.panels}>
        {items.map((it, i) => (
          <div
            key={it.tab}
            className={[styles.panel, i === current ? styles.isOpen : ""].filter(Boolean).join(" ")}
            role="tabpanel"
            id={`${uid}-p${i}`}
            aria-labelledby={`${uid}-t${i}`}
            aria-hidden={i !== current}
          >
            {/* 0fr 칸이 실제로 접히려면 이 래퍼에 min-height: 0 과 overflow: hidden 이 둘 다 있어야 한다 */}
            <div className={styles.clip}>
              <div className={styles.body}>
                <p className={styles.price}>{it.price}</p>
                <p className={styles.desc}>{it.desc}</p>
              </div>
            </div>
          </div>
        ))}
      </div>
    </section>
  );
}