06Fullscreen overlay where the burger folds into an X

<main class="stage">
  <div class="fm is-demo">
    <div class="fm__page" aria-hidden="true">
      <i class="fm__block fm__block--a"></i>
      <i class="fm__block fm__block--b"></i>
      <i class="fm__rule"></i>
      <i class="fm__rule fm__rule--s"></i>
      <i class="fm__rule fm__rule--m"></i>
    </div>
    <header class="fm__bar">
      <span class="fm__brand">Studio</span>
      <button class="fm__btn" type="button" aria-controls="fm-menu">
        <span class="fm__burger" aria-hidden="true"><span></span><span></span><span></span></span>
      </button>
    </header>
    <div class="fm__overlay" id="fm-menu" role="dialog" aria-modal="true" aria-label="Main menu">
      <a class="fm__link" style="--i: 0" href="#">Work
        <svg viewBox="0 0 256 256" width="18" height="18" aria-hidden="true"><g fill="currentColor"><path d="M192 64v104L88 64Z" opacity=".2"/><path d="M192 56H88a8 8 0 0 0-5.66 13.66L128.69 116l-70.35 70.34a8 8 0 0 0 11.32 11.32L140 127.31l46.34 46.35A8 8 0 0 0 200 168V64a8 8 0 0 0-8-8m-8 92.69l-38.34-38.34L107.31 72H184Z"/></g></svg>
      </a>
      <a class="fm__link" style="--i: 1" href="#">About
        <svg viewBox="0 0 256 256" width="18" height="18" aria-hidden="true"><g fill="currentColor"><path d="M192 64v104L88 64Z" opacity=".2"/><path d="M192 56H88a8 8 0 0 0-5.66 13.66L128.69 116l-70.35 70.34a8 8 0 0 0 11.32 11.32L140 127.31l46.34 46.35A8 8 0 0 0 200 168V64a8 8 0 0 0-8-8m-8 92.69l-38.34-38.34L107.31 72H184Z"/></g></svg>
      </a>
      <a class="fm__link" style="--i: 2" href="#">Log
        <svg viewBox="0 0 256 256" width="18" height="18" aria-hidden="true"><g fill="currentColor"><path d="M192 64v104L88 64Z" opacity=".2"/><path d="M192 56H88a8 8 0 0 0-5.66 13.66L128.69 116l-70.35 70.34a8 8 0 0 0 11.32 11.32L140 127.31l46.34 46.35A8 8 0 0 0 200 168V64a8 8 0 0 0-8-8m-8 92.69l-38.34-38.34L107.31 72H184Z"/></g></svg>
      </a>
      <a class="fm__link" style="--i: 3" href="#">Contact
        <svg viewBox="0 0 256 256" width="18" height="18" aria-hidden="true"><g fill="currentColor"><path d="M192 64v104L88 64Z" opacity=".2"/><path d="M192 56H88a8 8 0 0 0-5.66 13.66L128.69 116l-70.35 70.34a8 8 0 0 0 11.32 11.32L140 127.31l46.34 46.35A8 8 0 0 0 200 168V64a8 8 0 0 0-8-8m-8 92.69l-38.34-38.34L107.31 72H184Z"/></g></svg>
      </a>
    </div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;    // 격자 미리보기 루프 한 바퀴 2초
$easing: $ease-pop;      // 햄버거→X 모프와 오버레이 등장의 탄성
$color: $subject-cream;  // 잉크 무대 위 브랜드·막대·큰 링크

@include stage($stage-ink);

.fm, .fm * { box-sizing: border-box; }

.fm {
  position: relative;
  width: min(440px, 94vw);
  height: clamp(168px, 84vh, 264px);
  overflow: hidden;
  border-radius: $r-card;
  background: rgba(255, 247, 230, .04);
}

// ── 평소 화면: 상단 바 + 텍스트 없는 장식 조각 ──
.fm__bar {
  position: relative;
  z-index: 3;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: $sp-3 $sp-4;
}

.fm__brand { color: $color; font-size: 16px; line-height: 22px; font-weight: 800; transition: opacity 200ms linear; }
.fm.is-open .fm__brand { opacity: 0; }  // 열렸을 때는 X 닫기 버튼만 남는다

.fm__btn {
  display: grid;
  place-items: center;
  width: 40px;
  height: 40px;
  margin: 0;
  padding: 0;
  border: 0;
  border-radius: $r-control;
  background: rgba(255, 247, 230, .1);
  cursor: pointer;
}
.fm__btn:focus-visible { outline: 2px solid $color; outline-offset: 2px; }

// 햄버거는 아이콘이 아니라 막대 3개 span — 그 자체가 X 로 모프한다
.fm__burger { display: grid; gap: $sp-1; }
.fm__burger span {
  width: 20px;
  height: 2px;
  border-radius: $r-pill;
  background: $color;
  transition: transform 300ms $ease-pop, opacity 160ms linear;
}
.fm.is-open .fm__burger span:nth-child(1) { transform: translateY(6px) rotate(45deg); }
.fm.is-open .fm__burger span:nth-child(2) { transform: scaleX(0); opacity: 0; }
.fm.is-open .fm__burger span:nth-child(3) { transform: translateY(-6px) rotate(-45deg); }

// 페이지 장식 — 블록 두 개와 회색 막대 세 줄
.fm__page { display: flex; flex-direction: column; gap: $sp-2; padding: 0 $sp-4 $sp-3; }
.fm__block { border-radius: $r-sm; background: rgba(255, 247, 230, .1); }
.fm__block--a { height: clamp(40px, 20vh, 84px); }
.fm__block--b { height: clamp(20px, 10vh, 44px); background: rgba(255, 247, 230, .06); }
.fm__rule { height: 8px; border-radius: $r-xs; background: rgba(255, 247, 230, .14); }
.fm__rule--s { width: 64%; }
.fm__rule--m { width: 44%; }

// ── 풀스크린 오버레이 ── 겹침 크로스페이드가 아니라 새 레이어 등장(scale 1.06→1 + opacity).
//    닫힌 상태는 visibility: hidden + inert(JS) 로 포커스·탐색에서도 밖으로 내보낸다.
.fm__overlay {
  position: absolute;
  inset: 0;
  z-index: 2;
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: $sp-3;
  padding: 0 $sp-8;
  background: #241f2d;   // 잉크 무대보다 살짝 밝은 오버레이
  visibility: hidden;
  opacity: 0;
  transform: scale(1.06);
  transition: opacity 260ms $ease-out, transform 320ms $ease-pop, visibility 0s linear 320ms;
}
.fm.is-open .fm__overlay {
  visibility: visible;
  opacity: 1;
  transform: scale(1);
  transition: opacity 260ms $ease-out, transform 320ms $ease-pop, visibility 0s;
}

.fm__link {
  display: inline-flex;
  align-items: center;
  gap: $sp-2;
  color: $color;
  font-size: 24px;
  line-height: 32px;
  font-weight: 800;
  text-decoration: none;
  opacity: 0;
  transform: translateY(18px);
  transition: opacity 260ms $ease-out, transform 300ms $ease-pop;
}
.fm__link svg { opacity: .6; }
.fm__link:focus-visible { outline: 2px solid $color; outline-offset: 4px; border-radius: $r-xs; }
// 열릴 때만 시차 등장(--i × 80ms). 닫힘은 지연 없이 한꺼번에 — 퇴장은 짧게.
.fm.is-open .fm__link { opacity: 1; transform: translateY(0); transition-delay: calc(var(--i) * 80ms); }

// ── 격자 미리보기 루프 ──
//    0~7% 닫힘 → 8% 모프+오버레이 등장 → 12~48% 링크 시차 등장(등장이 주인공) →
//    72% 유지 → 76% 닫힘(짧게, 막대 역모프) → 84%부터 닫힌 채 대기.
.fm.is-demo .fm__overlay {
  visibility: visible;
  animation-name: fm-ov;
  animation-duration: $duration;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}
.fm.is-demo .fm__burger span,
.fm.is-demo .fm__link {
  animation-duration: $duration;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}
.fm.is-demo .fm__burger span:nth-child(1) { animation-name: fm-b1; }
.fm.is-demo .fm__burger span:nth-child(2) { animation-name: fm-b2; }
.fm.is-demo .fm__burger span:nth-child(3) { animation-name: fm-b3; }
.fm.is-demo .fm__link:nth-child(1) { animation-name: fm-l1; }
.fm.is-demo .fm__link:nth-child(2) { animation-name: fm-l2; }
.fm.is-demo .fm__link:nth-child(3) { animation-name: fm-l3; }
.fm.is-demo .fm__link:nth-child(4) { animation-name: fm-l4; }

@keyframes fm-ov {
  0%, 8.3% { opacity: 0; transform: scale(1.06); }
  8.4%, 74% { opacity: 1; transform: scale(1); }
  80%, 100% { opacity: 0; transform: scale(1); }
}
@keyframes fm-b1 {
  0%, 8.3% { transform: translateY(0) rotate(0deg); }
  18%, 78% { transform: translateY(6px) rotate(45deg); }
  88%, 100% { transform: translateY(0) rotate(0deg); }
}
@keyframes fm-b2 {
  0%, 8.3% { opacity: 1; transform: scaleX(1); }
  18%, 78% { opacity: 0; transform: scaleX(0); }
  88%, 100% { opacity: 1; transform: scaleX(1); }
}
@keyframes fm-b3 {
  0%, 8.3% { transform: translateY(0) rotate(0deg); }
  18%, 78% { transform: translateY(-6px) rotate(-45deg); }
  88%, 100% { transform: translateY(0) rotate(0deg); }
}
@keyframes fm-l1 { 0%, 12% { opacity: 0; transform: translateY(18px); } 24%, 100% { opacity: 1; transform: translateY(0); } }
@keyframes fm-l2 { 0%, 20% { opacity: 0; transform: translateY(18px); } 32%, 100% { opacity: 1; transform: translateY(0); } }
@keyframes fm-l3 { 0%, 28% { opacity: 0; transform: translateY(18px); } 40%, 100% { opacity: 1; transform: translateY(0); } }
@keyframes fm-l4 { 0%, 36% { opacity: 0; transform: translateY(18px); } 48%, 100% { opacity: 1; transform: translateY(0); } }

@media (max-width: 340px) {
  .fm__bar { padding: $sp-2 $sp-3; }
  .fm__brand { font-size: 14px; line-height: 20px; }
  .fm__btn { width: 36px; height: 36px; }
  .fm__page { gap: $sp-1; padding: 0 $sp-3 $sp-2; }
  .fm__rule { height: 6px; }
  .fm__overlay { gap: $sp-2; padding: 0 $sp-5; }
  .fm__link { font-size: 19px; line-height: 26px; }
}

@media (prefers-reduced-motion: reduce) {
  .fm.is-demo .fm__overlay,
  .fm.is-demo .fm__burger span,
  .fm.is-demo .fm__link { animation: none !important; }
  // 정적 상태에서 주인공(열린 메뉴)이 보이도록 연 채 둔다
  .fm.is-demo .fm__overlay { visibility: visible !important; opacity: 1 !important; transform: none !important; }
  .fm.is-demo .fm__link { opacity: 1 !important; transform: none !important; }
  .fm.is-demo .fm__burger span:nth-child(1) { transform: translateY(6px) rotate(45deg) !important; }
  .fm.is-demo .fm__burger span:nth-child(2) { opacity: 0 !important; transform: scaleX(0) !important; }
  .fm.is-demo .fm__burger span:nth-child(3) { transform: translateY(-6px) rotate(-45deg) !important; }
  .fm.is-demo .fm__brand { opacity: 0 !important; }
  .fm__burger span, .fm__overlay, .fm__link, .fm__brand { transition: none !important; transition-delay: 0ms !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);
}

.fm, .fm * {
  box-sizing: border-box;
}

.fm {
  position: relative;
  width: min(440px, 94vw);
  height: clamp(168px, 84vh, 264px);
  overflow: hidden;
  border-radius: 16px;
  background: rgba(255, 247, 230, 0.04);
}

.fm__bar {
  position: relative;
  z-index: 3;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 16px;
}

.fm__brand {
  color: #fff7e6;
  font-size: 16px;
  line-height: 22px;
  font-weight: 800;
  transition: opacity 200ms linear;
}

.fm.is-open .fm__brand {
  opacity: 0;
}

.fm__btn {
  display: grid;
  place-items: center;
  width: 40px;
  height: 40px;
  margin: 0;
  padding: 0;
  border: 0;
  border-radius: 12px;
  background: rgba(255, 247, 230, 0.1);
  cursor: pointer;
}

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

.fm__burger {
  display: grid;
  gap: 4px;
}

.fm__burger span {
  width: 20px;
  height: 2px;
  border-radius: 999px;
  background: #fff7e6;
  transition: transform 300ms cubic-bezier(0.2, 1.4, 0.4, 1), opacity 160ms linear;
}

.fm.is-open .fm__burger span:nth-child(1) {
  transform: translateY(6px) rotate(45deg);
}

.fm.is-open .fm__burger span:nth-child(2) {
  transform: scaleX(0);
  opacity: 0;
}

.fm.is-open .fm__burger span:nth-child(3) {
  transform: translateY(-6px) rotate(-45deg);
}

.fm__page {
  display: flex;
  flex-direction: column;
  gap: 8px;
  padding: 0 16px 12px;
}

.fm__block {
  border-radius: 8px;
  background: rgba(255, 247, 230, 0.1);
}

.fm__block--a {
  height: clamp(40px, 20vh, 84px);
}

.fm__block--b {
  height: clamp(20px, 10vh, 44px);
  background: rgba(255, 247, 230, 0.06);
}

.fm__rule {
  height: 8px;
  border-radius: 4px;
  background: rgba(255, 247, 230, 0.14);
}

.fm__rule--s {
  width: 64%;
}

.fm__rule--m {
  width: 44%;
}

.fm__overlay {
  position: absolute;
  inset: 0;
  z-index: 2;
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 12px;
  padding: 0 32px;
  background: #241f2d;
  visibility: hidden;
  opacity: 0;
  transform: scale(1.06);
  transition: opacity 260ms ease-out, transform 320ms cubic-bezier(0.2, 1.4, 0.4, 1), visibility 0s linear 320ms;
}

.fm.is-open .fm__overlay {
  visibility: visible;
  opacity: 1;
  transform: scale(1);
  transition: opacity 260ms ease-out, transform 320ms cubic-bezier(0.2, 1.4, 0.4, 1), visibility 0s;
}

.fm__link {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  color: #fff7e6;
  font-size: 24px;
  line-height: 32px;
  font-weight: 800;
  text-decoration: none;
  opacity: 0;
  transform: translateY(18px);
  transition: opacity 260ms ease-out, transform 300ms cubic-bezier(0.2, 1.4, 0.4, 1);
}

.fm__link svg {
  opacity: 0.6;
}

.fm__link:focus-visible {
  outline: 2px solid #fff7e6;
  outline-offset: 4px;
  border-radius: 4px;
}

.fm.is-open .fm__link {
  opacity: 1;
  transform: translateY(0);
  transition-delay: calc(var(--i) * 80ms);
}

.fm.is-demo .fm__overlay {
  visibility: visible;
  animation-name: fm-ov;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 1.4, 0.4, 1);
  animation-iteration-count: infinite;
}

.fm.is-demo .fm__burger span,
.fm.is-demo .fm__link {
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 1.4, 0.4, 1);
  animation-iteration-count: infinite;
}

.fm.is-demo .fm__burger span:nth-child(1) {
  animation-name: fm-b1;
}

.fm.is-demo .fm__burger span:nth-child(2) {
  animation-name: fm-b2;
}

.fm.is-demo .fm__burger span:nth-child(3) {
  animation-name: fm-b3;
}

.fm.is-demo .fm__link:nth-child(1) {
  animation-name: fm-l1;
}

.fm.is-demo .fm__link:nth-child(2) {
  animation-name: fm-l2;
}

.fm.is-demo .fm__link:nth-child(3) {
  animation-name: fm-l3;
}

.fm.is-demo .fm__link:nth-child(4) {
  animation-name: fm-l4;
}

@keyframes fm-ov {
  0%, 8.3% {
    opacity: 0;
    transform: scale(1.06);
  }
  8.4%, 74% {
    opacity: 1;
    transform: scale(1);
  }
  80%, 100% {
    opacity: 0;
    transform: scale(1);
  }
}
@keyframes fm-b1 {
  0%, 8.3% {
    transform: translateY(0) rotate(0deg);
  }
  18%, 78% {
    transform: translateY(6px) rotate(45deg);
  }
  88%, 100% {
    transform: translateY(0) rotate(0deg);
  }
}
@keyframes fm-b2 {
  0%, 8.3% {
    opacity: 1;
    transform: scaleX(1);
  }
  18%, 78% {
    opacity: 0;
    transform: scaleX(0);
  }
  88%, 100% {
    opacity: 1;
    transform: scaleX(1);
  }
}
@keyframes fm-b3 {
  0%, 8.3% {
    transform: translateY(0) rotate(0deg);
  }
  18%, 78% {
    transform: translateY(-6px) rotate(-45deg);
  }
  88%, 100% {
    transform: translateY(0) rotate(0deg);
  }
}
@keyframes fm-l1 {
  0%, 12% {
    opacity: 0;
    transform: translateY(18px);
  }
  24%, 100% {
    opacity: 1;
    transform: translateY(0);
  }
}
@keyframes fm-l2 {
  0%, 20% {
    opacity: 0;
    transform: translateY(18px);
  }
  32%, 100% {
    opacity: 1;
    transform: translateY(0);
  }
}
@keyframes fm-l3 {
  0%, 28% {
    opacity: 0;
    transform: translateY(18px);
  }
  40%, 100% {
    opacity: 1;
    transform: translateY(0);
  }
}
@keyframes fm-l4 {
  0%, 36% {
    opacity: 0;
    transform: translateY(18px);
  }
  48%, 100% {
    opacity: 1;
    transform: translateY(0);
  }
}
@media (max-width: 340px) {
  .fm__bar {
    padding: 8px 12px;
  }
  .fm__brand {
    font-size: 14px;
    line-height: 20px;
  }
  .fm__btn {
    width: 36px;
    height: 36px;
  }
  .fm__page {
    gap: 4px;
    padding: 0 12px 8px;
  }
  .fm__rule {
    height: 6px;
  }
  .fm__overlay {
    gap: 8px;
    padding: 0 20px;
  }
  .fm__link {
    font-size: 19px;
    line-height: 26px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .fm.is-demo .fm__overlay,
  .fm.is-demo .fm__burger span,
  .fm.is-demo .fm__link {
    animation: none !important;
  }
  .fm.is-demo .fm__overlay {
    visibility: visible !important;
    opacity: 1 !important;
    transform: none !important;
  }
  .fm.is-demo .fm__link {
    opacity: 1 !important;
    transform: none !important;
  }
  .fm.is-demo .fm__burger span:nth-child(1) {
    transform: translateY(6px) rotate(45deg) !important;
  }
  .fm.is-demo .fm__burger span:nth-child(2) {
    opacity: 0 !important;
    transform: scaleX(0) !important;
  }
  .fm.is-demo .fm__burger span:nth-child(3) {
    transform: translateY(-6px) rotate(-45deg) !important;
  }
  .fm.is-demo .fm__brand {
    opacity: 0 !important;
  }
  .fm__burger span, .fm__overlay, .fm__link, .fm__brand {
    transition: none !important;
    transition-delay: 0ms !important;
  }
}

// 실제 동작: 버튼 하나가 열기/닫기를 겸한다 — 햄버거 막대가 X 로 모프한다.
var fm = document.querySelector('.fm');
var btn = fm.querySelector('.fm__btn');
var ov = fm.querySelector('.fm__overlay');
var links = Array.prototype.slice.call(ov.querySelectorAll('.fm__link'));
btn.setAttribute('aria-haspopup', 'true');
btn.setAttribute('aria-expanded', 'false');
ov.setAttribute('inert', '');
function stopDemo() { fm.classList.remove('is-demo'); }  // 사람이 만졌으니 자동 루프를 끈다
fm.addEventListener('pointerdown', stopDemo);
function open() {
  fm.classList.add('is-open');
  btn.setAttribute('aria-expanded', 'true');
  ov.removeAttribute('inert');
  btn.focus({ preventScroll: true });   // 같은 버튼이 X 닫기가 된다 — 초점 유지
}
function close() {
  fm.classList.remove('is-open');
  btn.setAttribute('aria-expanded', 'false');
  ov.setAttribute('inert', '');
  btn.focus({ preventScroll: true });
}
btn.addEventListener('click', function () {
  fm.classList.contains('is-open') ? close() : open();
});
// Tab 이 오버레이 밖으로 나가면 다시 안으로 돌린다(포커스 트랩)
ov.addEventListener('keydown', function (e) {
  if (e.key !== 'Tab' || links.length === 0) return;
  var first = links[0], last = links[links.length - 1];
  if (e.shiftKey && document.activeElement === first) {
    e.preventDefault(); last.focus({ preventScroll: true });
  } else if (!e.shiftKey && document.activeElement === last) {
    e.preventDefault(); first.focus({ preventScroll: true });
  }
});
// Escape Close — 초점은 버튼으로
fm.addEventListener('keydown', function (e) {
  if (e.key === 'Escape' && fm.classList.contains('is-open')) close();
});

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

export type FullscreenMorphProps = {
  labels?: { brand?: string; menuLabel?: string; links?: 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 };
type Box<T> = { current: T | null };
type KeyEvt = { key: string; shiftKey: boolean; preventDefault(): void };

const LINKS = ["Work", "About", "Log", "Contact"];

const ARROW = (
  <g fill="currentColor">
    <path d="M192 64v104L88 64Z" opacity=".2" />
    <path d="M192 56H88a8 8 0 0 0-5.66 13.66L128.69 116l-70.35 70.34a8 8 0 0 0 11.32 11.32L140 127.31l46.34 46.35A8 8 0 0 0 200 168V64a8 8 0 0 0-8-8m-8 92.69l-38.34-38.34L107.31 72H184Z" />
  </g>
);

export default function FullscreenMorph({
  labels,
  demo = true,
  duration = 2000,
  easing = "cubic-bezier(.2, 1.4, .4, 1)",
  color = "#fff7e6",
}: FullscreenMorphProps) {
  const brand = labels?.brand ?? "Studio";
  const menuLabel = labels?.menuLabel ?? "Main menu";
  const links = labels?.links ?? LINKS;

  const [live, setLive] = useState(demo);
  const [open, setOpen] = useState(false);
  const btnRef: Box<HTMLButtonElement> = useRef(null);
  const ovRef: Box<HTMLDivElement> = useRef(null);

  // 닫힌 오버레이는 포커스·탐색에서도 밖으로 내보낸다(inert)
  useEffect(() => {
    const ov = ovRef.current;
    if (ov === null) return;
    if (open) ov.removeAttribute("inert");
    else ov.setAttribute("inert", "");
  }, [open]);

  function toggle() {
    setLive(false); // 사람이 만졌으니 자동 루프를 끈다
    setOpen(!open);
    const b = btnRef.current; // 같은 버튼이 X 닫기가 된다 — 초점 유지
    if (b !== null) b.focus({ preventScroll: true });
  }

  // Escape 닫기 + Tab 이 오버레이 밖으로 나가면 다시 안으로(포커스 트랩)
  function keys(e: KeyEvt) {
    setLive(false);
    if (e.key === "Escape" && open) {
      setOpen(false);
      const b = btnRef.current;
      if (b !== null) b.focus({ preventScroll: true });
      return;
    }
    if (e.key !== "Tab" || !open) return;
    const ov = ovRef.current;
    if (ov === null) return;
    const els = Array.from(ov.querySelectorAll("a")) as HTMLElement[];
    if (els.length === 0) return;
    const first = els[0];
    const last = els[els.length - 1];
    const el = document.activeElement;
    if (e.shiftKey && el === first) {
      e.preventDefault();
      last.focus({ preventScroll: true });
    } else if (!e.shiftKey && el === last) {
      e.preventDefault();
      first.focus({ preventScroll: true });
    }
  }

  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  const cls = [styles.fm, live ? styles.isDemo : "", open ? styles.isOpen : ""].filter(Boolean).join(" ");

  return (
    <section className={cls} style={vars} onPointerDown={() => setLive(false)} onKeyDown={keys}>
      <div className={styles.page} aria-hidden="true">
        <i className={`${styles.block} ${styles.blockA}`} />
        <i className={`${styles.block} ${styles.blockB}`} />
        <i className={styles.rule} />
        <i className={`${styles.rule} ${styles.ruleS}`} />
        <i className={`${styles.rule} ${styles.ruleM}`} />
      </div>
      <header className={styles.bar}>
        <span className={styles.brand}>{brand}</span>
        <button
          className={styles.btn}
          type="button"
          aria-haspopup="true"
          aria-expanded={open}
          aria-controls="fm-menu"
          ref={btnRef}
          onClick={toggle}
        >
          <span className={styles.burger} aria-hidden="true"><span /><span /><span /></span>
        </button>
      </header>
      <div
        className={styles.overlay}
        id="fm-menu"
        role="dialog"
        aria-modal="true"
        aria-label={menuLabel}
        ref={ovRef}
      >
        {links.map((t, i) => (
          <a className={styles.link} key={t} href="#" style={{ "--i": i } as CSSProperties}>
            {t}
            <svg viewBox="0 0 256 256" width="18" height="18" aria-hidden="true">{ARROW}</svg>
          </a>
        ))}
      </div>
    </section>
  );
}