09シェブロンがばねで回り、選ぶとラベルが上がるセレクト欄

<main class="stage">
  <div class="fl is-demo" id="fl" data-demo="1">
    <div class="fl__field">
      <div class="fl__box" data-r="box">
        <button class="fl__input fl__select" id="c1" data-r="btn" type="button" role="combobox" aria-haspopup="listbox" aria-expanded="false" aria-controls="m1">
          <span class="fl__val" data-r="val"></span>
        </button>
        <label class="fl__label" for="c1" id="l1" data-r="label">市区町村</label>
        <svg class="fl__chev" data-r="chev" aria-hidden="true" width="24" height="24" viewBox="0 0 256 256"><g fill="currentColor"><path d="m208 96l-80 80l-80-80Z" opacity=".2"/><path d="M215.39 92.94A8 8 0 0 0 208 88H48a8 8 0 0 0-5.66 13.66l80 80a8 8 0 0 0 11.32 0l80-80a8 8 0 0 0 1.73-8.72M128 164.69L67.31 104h121.38Z"/></g></svg>
        <ul class="fl__menu" id="m1" role="listbox" aria-labelledby="l1" data-r="menu">
          <li class="fl__opt" role="option" id="m1o0" data-r="opt" aria-selected="false">ソウル</li>
          <li class="fl__opt" role="option" id="m1o1" data-r="opt" aria-selected="false">釜山</li>
          <li class="fl__opt" role="option" id="m1o2" data-r="opt" aria-selected="false">済州</li>
        </ul>
      </div>
    </div>
    <div class="fl__field">
      <div class="fl__box" data-r="box">
        <button class="fl__input fl__select" id="c2" data-r="btn" type="button" role="combobox" aria-haspopup="listbox" aria-expanded="false" aria-controls="m2">
          <span class="fl__val" data-r="val"></span>
        </button>
        <label class="fl__label" for="c2" id="l2" data-r="label">曜日</label>
        <svg class="fl__chev" data-r="chev" aria-hidden="true" width="24" height="24" viewBox="0 0 256 256"><g fill="currentColor"><path d="m208 96l-80 80l-80-80Z" opacity=".2"/><path d="M215.39 92.94A8 8 0 0 0 208 88H48a8 8 0 0 0-5.66 13.66l80 80a8 8 0 0 0 11.32 0l80-80a8 8 0 0 0 1.73-8.72M128 164.69L67.31 104h121.38Z"/></g></svg>
        <ul class="fl__menu fl__menu--up" id="m2" role="listbox" aria-labelledby="l2" data-r="menu">
          <li class="fl__opt" role="option" id="m2o0" data-r="opt" aria-selected="false">月曜日</li>
          <li class="fl__opt" role="option" id="m2o1" data-r="opt" aria-selected="false">水曜日</li>
          <li class="fl__opt" role="option" id="m2o2" data-r="opt" aria-selected="false">金曜日</li>
        </ul>
      </div>
    </div>
  </div>
</main>

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

// 핵심: 열림 각도 스프링 하나에서 쉐브론·목록 높이·라벨 상승을 모두 파생한다. 라벨은 진짜 <label for> 이고 칸은 진짜 입력 요소다. 움직임 값은 JS 가 계산하고 CSS 는 모양만 맡는다.

@include stage($stage-ink);

$panel: mix($subject-cream, $stage-ink, 8%);
$box-bg: mix($subject-cream, $stage-ink, 5%);
$fg: $subject-cream;
$mute: $tick-mute;
$line: mix($subject-cream, $stage-ink, 32%);
$accent: $subject-lilac;
$err: $tick-down;
$menu-bg: mix($subject-cream, $stage-ink, 16%);
$box-h: 52px;

.fl {
  position: relative;
  box-sizing: border-box;
  width: min(100%, 440px);
  padding: $sp-5;
  display: flex;
  flex-direction: column;
  gap: $sp-4;
  border-radius: $r-card;
  background: $panel;
  color: $fg;
  font-size: 16px;
  line-height: 24px;
  font-weight: 500;
}
.fl__field { position: relative; }
.fl__box {
  --ln: #{$line};
  position: relative;
  z-index: 1;
  height: $box-h;
  border-radius: $r-sm;
  background: $box-bg;
  box-shadow: inset 0 0 0 1.5px var(--ln), 0 0 0 calc(var(--p, 0) * 3px) rgba($accent, .3);
}
.fl__box[data-up] { --ln: #{$accent}; }
.fl__box::after {
  content: "";
  position: absolute;
  inset: 0;
  z-index: 0;
  border-radius: inherit;
  background: $accent;
  opacity: calc(var(--p, 0) * .12);
  pointer-events: none;
}
.fl__input {
  position: relative;
  z-index: 1;
  box-sizing: border-box;
  display: block;
  width: 100%;
  height: 100%;
  margin: 0;
  padding: $sp-6 $sp-3 $sp-1;
  border: 0;
  border-radius: inherit;
  background: transparent;
  color: $fg;
  font-family: inherit;
  font-size: 16px;
  line-height: 24px;
  font-weight: 500;
  outline: none;
}
.fl__input:focus-visible { outline: 2px solid $accent; outline-offset: 2px; }
.fl__label {
  position: absolute;
  left: $sp-3;
  top: 0;
  z-index: 2;
  line-height: $box-h;
  font-size: 16px;
  font-weight: 500;
  color: $mute;
  white-space: nowrap;
  transform-origin: 0 50%;
  pointer-events: none;
  will-change: transform;
}
.fl__box[data-up] .fl__label { color: $accent; }
.fl__box { --ln: #{$line}; }
.fl__box[data-open] { z-index: 6; --ln: #{$accent}; }
.fl__select { padding-right: 48px; text-align: left; cursor: pointer; }
.fl__val { display: block; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.fl__chev { position: absolute; right: $sp-3; top: calc(50% - #{$sp-3}); z-index: 2; width: 24px; height: 24px; color: $mute; pointer-events: none; will-change: transform; }
.fl__box[data-open] .fl__chev { color: $accent; }
.fl__menu {
  position: absolute;
  left: 0;
  right: 0;
  top: calc(100% + #{$sp-1});
  z-index: 5;
  box-sizing: border-box;
  height: 0;
  margin: 0;
  padding: $sp-1;
  overflow: hidden;
  list-style: none;
  border-radius: $r-sm;
  background: $menu-bg;
  box-shadow: $shadow-press;
  opacity: 0;
  visibility: hidden;
}
.fl__menu--up { top: auto; bottom: calc(100% + #{$sp-1}); }
.fl__opt {
  box-sizing: border-box;
  height: 36px;
  padding: 0 $sp-3;
  border-radius: $r-xs;
  font-size: 16px;
  line-height: 36px;
  color: $fg;
  cursor: pointer;
}
.fl__opt[data-hi] { background: rgba($accent, .2); }
.fl__opt[aria-selected="true"] { font-weight: 700; }
@media (max-height: 250px) {
  .fl__field:nth-child(n + 3) { display: none; }
}
@media (prefers-reduced-motion: reduce) {
  .fl__label, .fl__box { will-change: auto; }
}

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);
}

.fl {
  position: relative;
  box-sizing: border-box;
  width: min(100%, 440px);
  padding: 20px;
  display: flex;
  flex-direction: column;
  gap: 16px;
  border-radius: 16px;
  background: rgb(16.2980392157%, 14.9647058824%, 16.5960784314%);
  color: #fff7e6;
  font-size: 16px;
  line-height: 24px;
  font-weight: 500;
}

.fl__field {
  position: relative;
}

.fl__box {
  --ln: rgb(38.1333333333%, 36.3294117647%, 35.7960784314%);
  position: relative;
  z-index: 1;
  height: 52px;
  border-radius: 8px;
  background: rgb(13.568627451%, 12.2941176471%, 14.1960784314%);
  box-shadow: inset 0 0 0 1.5px var(--ln), 0 0 0 calc(var(--p, 0) * 3px) rgba(185, 160, 255, 0.3);
}

.fl__box[data-up] {
  --ln: #b9a0ff;
}

.fl__box::after {
  content: "";
  position: absolute;
  inset: 0;
  z-index: 0;
  border-radius: inherit;
  background: #b9a0ff;
  opacity: calc(var(--p, 0) * 0.12);
  pointer-events: none;
}

.fl__input {
  position: relative;
  z-index: 1;
  box-sizing: border-box;
  display: block;
  width: 100%;
  height: 100%;
  margin: 0;
  padding: 24px 12px 4px;
  border: 0;
  border-radius: inherit;
  background: transparent;
  color: #fff7e6;
  font-family: inherit;
  font-size: 16px;
  line-height: 24px;
  font-weight: 500;
  outline: none;
}

.fl__input:focus-visible {
  outline: 2px solid #b9a0ff;
  outline-offset: 2px;
}

.fl__label {
  position: absolute;
  left: 12px;
  top: 0;
  z-index: 2;
  line-height: 52px;
  font-size: 16px;
  font-weight: 500;
  color: #9a93a6;
  white-space: nowrap;
  transform-origin: 0 50%;
  pointer-events: none;
  will-change: transform;
}

.fl__box[data-up] .fl__label {
  color: #b9a0ff;
}

.fl__box {
  --ln: rgb(38.1333333333%, 36.3294117647%, 35.7960784314%);
}

.fl__box[data-open] {
  z-index: 6;
  --ln: #b9a0ff;
}

.fl__select {
  padding-right: 48px;
  text-align: left;
  cursor: pointer;
}

.fl__val {
  display: block;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.fl__chev {
  position: absolute;
  right: 12px;
  top: calc(50% - 12px);
  z-index: 2;
  width: 24px;
  height: 24px;
  color: #9a93a6;
  pointer-events: none;
  will-change: transform;
}

.fl__box[data-open] .fl__chev {
  color: #b9a0ff;
}

.fl__menu {
  position: absolute;
  left: 0;
  right: 0;
  top: calc(100% + 4px);
  z-index: 5;
  box-sizing: border-box;
  height: 0;
  margin: 0;
  padding: 4px;
  overflow: hidden;
  list-style: none;
  border-radius: 8px;
  background: rgb(23.5764705882%, 22.0862745098%, 22.9960784314%);
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  opacity: 0;
  visibility: hidden;
}

.fl__menu--up {
  top: auto;
  bottom: calc(100% + 4px);
}

.fl__opt {
  box-sizing: border-box;
  height: 36px;
  padding: 0 12px;
  border-radius: 4px;
  font-size: 16px;
  line-height: 36px;
  color: #fff7e6;
  cursor: pointer;
}

.fl__opt[data-hi] {
  background: rgba(185, 160, 255, 0.2);
}

.fl__opt[aria-selected=true] {
  font-weight: 700;
}

@media (max-height: 250px) {
  .fl__field:nth-child(n+3) {
    display: none;
  }
}
@media (prefers-reduced-motion: reduce) {
  .fl__label, .fl__box {
    will-change: auto;
  }
}

(function () {
    const root = document.getElementById("fl");
    const CLS = {};
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let raf = 0;
    let last = -1;
    const offs = [];
    function q(sel) {
        return root.querySelector(sel);
    }
    function qa(sel) {
        const list = Array.prototype.slice.call(root.querySelectorAll(sel));
        return list;
    }
    function clamp(v, lo, hi) {
        return Math.max(lo, Math.min(hi, v));
    }
    function on(el, type, fn) {
        el.addEventListener(type, fn);
        offs.push(function () {
            el.removeEventListener(type, fn);
        });
    }
    // 좌표 해시: 같은 입력이면 같은 값 0~1. 난수 함수를 쓰지 않고 사인의 소수부만 쓴다.
    function hash(x) {
        const s = Math.sin(x * 127.1 + 311.7) * 43758.5453;
        return s - Math.floor(s);
    }
    // 지수 접근: 프레임당 비율 per 만큼 목표에 다가간다. f 는 60fps 기준 프레임 수(dt * 60)라 프레임률이 달라도 같은 속도다.
    function approach(x, target, per, f) {
        return x + (target - x) * (1 - Math.pow(1 - per, f));
    }
    // 스프링 한 칸: 가속도 = -k (x - 목표) - c v. 반암시적 오일러를 1/120초 이하 부분 스텝으로 쪼갠다.
    function springStep(s, target, k, c, dt) {
        let left = dt;
        while (left > 0) {
            const h = Math.min(left, 1 / 120);
            s.v += (-k * (s.x - target) - c * s.v) * h;
            s.x += s.v * h;
            left -= h;
        }
    }
    // 값이 있으면 라벨은 올라가 있어야 한다. 브라우저 자동완성이 값을 채우면 input 이벤트가 없을 수 있어 :autofill 도 함께 본다.
    function isFilled(el) {
        if (el.value !== "") return true;
        try {
            return el.matches(":-webkit-autofill");
        } catch (err) {
            return false;
        }
    }
    let leaveHook = null;
    function stopDemo() {
        if (!demo) return;
        demo = false;
        root.removeAttribute("data-demo");
        root.classList.remove("is-demo");
        resetFields();
    }
    function frame(ts) {
        const dt = last < 0 ? 0.016 : Math.min(0.05, (ts - last) / 1000);
        last = ts;
        if (demo) script(ts);
        step(dt, ts);
        render();
        raf = requestAnimationFrame(frame);
    }
    const ro = new ResizeObserver(function () {
        relayout();
    });
    ro.observe(root);
    if (document.fonts) {
        document.fonts.ready.then(function () {
            relayout();
        });
    }

    // 기법: 열림 정도 x 하나를 스프링으로 돌리고, 쉐브론 각도·목록 높이·라벨 상승을 전부 그 x 에서 파생한다. 값이 하나라 셋이 어긋날 수 없다.
    const CHEV_STIFF = 160;
    const CHEV_DAMP = 13;
    const OPEN_DEG = 180;
    const PICK_DELAY = 220;
    const OPT_H = 36;
    const MENU_PAD = 4;
    const RISE_PX = 15;
    const LABEL_SCALE = 0.74;
    const fields = qa("[data-r=box]").map(function (box) {
        const menu = box.querySelector("[data-r=menu]");
        const opts = Array.prototype.slice.call(menu.querySelectorAll("[data-r=opt]"));
        return {
            box: box,
            btn: box.querySelector("[data-r=btn]"),
            val: box.querySelector("[data-r=val]"),
            label: box.querySelector("[data-r=label]"),
            chev: box.querySelector("[data-r=chev]"),
            menu: menu, opts: opts,
            open: false, hi: 0, sel: -1, sp: { x: 0, v: 0 }, closeIn: 0
        };
    });
    // 이벤트 표: [시각(ms), 칸, 동작, 값]. 2초 주기로 되풀이한다.
    const EVENTS = [
        [200, 0, "open", 0],
        [480, 0, "hi", 1],
        [720, 0, "hi", 2],
        [980, 0, "pick", 2],
        [1250, 1, "open", 0],
        [1500, 1, "hi", 1],
        [1720, 1, "pick", 1]
    ];
    let lastT = -1;
    function syncAria(f) {
        f.btn.setAttribute("aria-expanded", String(f.open));
        if (f.open) {
            f.btn.setAttribute("aria-activedescendant", f.opts[f.hi].id);
            f.box.setAttribute("data-open", "");
        } else {
            f.btn.removeAttribute("aria-activedescendant");
            f.box.removeAttribute("data-open");
        }
        f.opts.forEach(function (o, i) {
            if (i === f.hi && f.open) o.setAttribute("data-hi", "");
            else o.removeAttribute("data-hi");
            o.setAttribute("aria-selected", String(i === f.sel));
        });
        f.val.textContent = f.sel >= 0 ? f.opts[f.sel].textContent : "";
        if (reduce) {
            f.sp.x = f.open ? 1 : 0;
            f.sp.v = 0;
            render();
        }
    }
    function setOpen(f, v) {
        f.open = v;
        f.closeIn = 0;
        if (v && f.sel >= 0) f.hi = f.sel;
        syncAria(f);
    }
    function pick(f, idx) {
        f.sel = idx;
        f.hi = idx;
        if (reduce) setOpen(f, false);
        else {
            f.closeIn = PICK_DELAY / 1000;
            syncAria(f);
        }
    }
    function move(f, to) {
        f.hi = clamp(to, 0, f.opts.length - 1);
        syncAria(f);
    }
    function resetFields() {
        fields.forEach(function (f) {
            f.sel = -1;
            f.hi = 0;
            setOpen(f, false);
        });
    }
    function relayout() {
        fields.forEach(syncAria);
    }
    function script(ts) {
        const t = ts % 2000;
        if (lastT < 0) lastT = t;
        if (t < lastT) resetFields();
        EVENTS.forEach(function (e) {
            if (e[0] <= lastT || e[0] > t) return;
            const f = fields[e[1]];
            if (e[2] === "open") setOpen(f, true);
            else if (e[2] === "hi") move(f, e[3]);
            else pick(f, e[3]);
        });
        lastT = t;
    }
    function step(dt, ts) {
        fields.forEach(function (f) {
            springStep(f.sp, f.open ? 1 : 0, CHEV_STIFF, CHEV_DAMP, dt);
            if (f.closeIn > 0) {
                f.closeIn -= dt;
                if (f.closeIn <= 0) setOpen(f, false);
            }
        });
    }
    function render() {
        fields.forEach(function (f) {
            const x = f.sp.x;
            const o = clamp(x, 0, 1);
            const r = f.sel >= 0 ? Math.max(1, clamp(x, 0, 1.25)) : clamp(x, 0, 1.25);
            const s = 1 - (1 - LABEL_SCALE) * r;
            f.label.style.transform = "translate3d(0," + (-RISE_PX * r).toFixed(2) + "px,0) scale(" + s.toFixed(3) + ")";
            f.chev.style.transform = "rotate(" + (OPEN_DEG * x).toFixed(1) + "deg)";
            f.box.style.setProperty("--p", clamp(r, 0, 1).toFixed(3));
            const h = (OPT_H * f.opts.length + 2 * MENU_PAD) * o;
            f.menu.style.height = h.toFixed(1) + "px";
            f.menu.style.opacity = clamp(o * 1.6, 0, 1).toFixed(3);
            f.menu.style.visibility = h < 1 ? "hidden" : "visible";
        });
    }
    fields.forEach(function (f) {
        f.opts.forEach(function (o, k) {
            on(o, "pointerenter", function () {
                if (f.open) move(f, k);
            });
            on(o, "click", function () {
                stopDemo();
                pick(f, k);
            });
        });
        // 목록을 누를 때 버튼이 포커스를 잃어 닫히지 않게 한다.
        on(f.menu, "mousedown", function (e) {
            e.preventDefault();
        });
        on(f.btn, "click", function (e) {
            stopDemo();
            if (e.detail === 0 && f.open) pick(f, f.hi);
            else setOpen(f, !f.open);
        });
        on(f.btn, "keydown", function (e) {
            if (e.key === "ArrowDown" || e.key === "ArrowUp") {
                e.preventDefault();
                stopDemo();
                if (!f.open) setOpen(f, true);
                else move(f, f.hi + (e.key === "ArrowDown" ? 1 : -1));
            } else if (e.key === "Escape" && f.open) {
                setOpen(f, false);
            }
        });
        on(f.btn, "blur", function () {
            if (f.open) setOpen(f, false);
        });
    });
    on(document, "pointerdown", function (e) {
        fields.forEach(function (f) {
            if (f.open && !f.box.contains(e.target)) setOpen(f, false);
        });
    });

    relayout();
    if (reduce) {
        render();
    } else {
        raf = requestAnimationFrame(frame);
    }

})();

// SelectChevronFloat - vanilla 판(09-fl-select-chevron-float) 의 React 포트. 같은 계산을 useEffect 안에서 돌린다.
import { useEffect, useRef } from "react";
import styles from "./SelectChevronFloat.module.scss";

type Spring = { x: number; v: number };
type Plan = { a: number; b: number; s: number; rate: number; text: string };
type Base = { input: HTMLInputElement | HTMLTextAreaElement; focus: boolean; up: boolean };
type F = { box: HTMLElement; btn: HTMLElement; val: HTMLElement; label: HTMLElement; chev: HTMLElement; menu: HTMLElement; opts: HTMLElement[]; open: boolean; hi: number; sel: number; sp: Spring; closeIn: number };

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

  useEffect(() => {
    const rootEl = rootRef.current;
    if (!rootEl) return;
    const root: HTMLElement = rootEl;
    const CLS = {  };
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let demo = !reduce;
    let raf: number = 0;
    let last: number = -1;
    const offs: Array<() => void> = [];
    function q(sel: string): HTMLElement {
        return root.querySelector(sel) as HTMLElement;
    }
    function qa(sel: string): HTMLElement[] {
        const list: HTMLElement[] = Array.prototype.slice.call(root.querySelectorAll(sel));
        return list;
    }
    function clamp(v: number, lo: number, hi: number): number {
        return Math.max(lo, Math.min(hi, v));
    }
    function on(el: EventTarget, type: string, fn: (e: any) => void): void {
        el.addEventListener(type, fn);
        offs.push(function (): void {
            el.removeEventListener(type, fn);
        });
    }
    // 좌표 해시: 같은 입력이면 같은 값 0~1. 난수 함수를 쓰지 않고 사인의 소수부만 쓴다.
    function hash(x: number): number {
        const s = Math.sin(x * 127.1 + 311.7) * 43758.5453;
        return s - Math.floor(s);
    }
    // 지수 접근: 프레임당 비율 per 만큼 목표에 다가간다. f 는 60fps 기준 프레임 수(dt * 60)라 프레임률이 달라도 같은 속도다.
    function approach(x: number, target: number, per: number, f: number): number {
        return x + (target - x) * (1 - Math.pow(1 - per, f));
    }
    // 스프링 한 칸: 가속도 = -k (x - 목표) - c v. 반암시적 오일러를 1/120초 이하 부분 스텝으로 쪼갠다.
    function springStep(s: Spring, target: number, k: number, c: number, dt: number): void {
        let left = dt;
        while (left > 0) {
            const h = Math.min(left, 1 / 120);
            s.v += (-k * (s.x - target) - c * s.v) * h;
            s.x += s.v * h;
            left -= h;
        }
    }
    // 값이 있으면 라벨은 올라가 있어야 한다. 브라우저 자동완성이 값을 채우면 input 이벤트가 없을 수 있어 :autofill 도 함께 본다.
    function isFilled(el: HTMLInputElement | HTMLTextAreaElement): boolean {
        if (el.value !== "") return true;
        try {
            return el.matches(":-webkit-autofill");
        } catch (err) {
            return false;
        }
    }
    let leaveHook: ((i: number) => void) | null = null;
    function stopDemo(): void {
        if (!demo) return;
        demo = false;
        root.removeAttribute("data-demo");
        root.classList.remove("is-demo");
        resetFields();
    }
    function frame(ts: number): void {
        const dt = last < 0 ? 0.016 : Math.min(0.05, (ts - last) / 1000);
        last = ts;
        if (demo) script(ts);
        step(dt, ts);
        render();
        raf = requestAnimationFrame(frame);
    }
    const ro = new ResizeObserver(function (): void {
        relayout();
    });
    ro.observe(root);
    if (document.fonts) {
        document.fonts.ready.then(function (): void {
            relayout();
        });
    }

    // 기법: 열림 정도 x 하나를 스프링으로 돌리고, 쉐브론 각도·목록 높이·라벨 상승을 전부 그 x 에서 파생한다. 값이 하나라 셋이 어긋날 수 없다.
    const CHEV_STIFF = 160;
    const CHEV_DAMP = 13;
    const OPEN_DEG = 180;
    const PICK_DELAY = 220;
    const OPT_H = 36;
    const MENU_PAD = 4;
    const RISE_PX = 15;
    const LABEL_SCALE = 0.74;
    const fields: F[] = qa("[data-r=box]").map(function (box: HTMLElement): F {
        const menu = box.querySelector("[data-r=menu]") as HTMLElement;
        const opts: HTMLElement[] = Array.prototype.slice.call(menu.querySelectorAll("[data-r=opt]"));
        return {
            box: box,
            btn: box.querySelector("[data-r=btn]") as HTMLElement,
            val: box.querySelector("[data-r=val]") as HTMLElement,
            label: box.querySelector("[data-r=label]") as HTMLElement,
            chev: box.querySelector("[data-r=chev]") as HTMLElement,
            menu: menu, opts: opts,
            open: false, hi: 0, sel: -1, sp: { x: 0, v: 0 }, closeIn: 0
        };
    });
    // 이벤트 표: [시각(ms), 칸, 동작, 값]. 2초 주기로 되풀이한다.
    const EVENTS: Array<[number, number, string, number]> = [
        [200, 0, "open", 0],
        [480, 0, "hi", 1],
        [720, 0, "hi", 2],
        [980, 0, "pick", 2],
        [1250, 1, "open", 0],
        [1500, 1, "hi", 1],
        [1720, 1, "pick", 1]
    ];
    let lastT = -1;
    function syncAria(f: F): void {
        f.btn.setAttribute("aria-expanded", String(f.open));
        if (f.open) {
            f.btn.setAttribute("aria-activedescendant", f.opts[f.hi].id);
            f.box.setAttribute("data-open", "");
        } else {
            f.btn.removeAttribute("aria-activedescendant");
            f.box.removeAttribute("data-open");
        }
        f.opts.forEach(function (o: HTMLElement, i: number): void {
            if (i === f.hi && f.open) o.setAttribute("data-hi", "");
            else o.removeAttribute("data-hi");
            o.setAttribute("aria-selected", String(i === f.sel));
        });
        f.val.textContent = f.sel >= 0 ? f.opts[f.sel].textContent : "";
        if (reduce) {
            f.sp.x = f.open ? 1 : 0;
            f.sp.v = 0;
            render();
        }
    }
    function setOpen(f: F, v: boolean): void {
        f.open = v;
        f.closeIn = 0;
        if (v && f.sel >= 0) f.hi = f.sel;
        syncAria(f);
    }
    function pick(f: F, idx: number): void {
        f.sel = idx;
        f.hi = idx;
        if (reduce) setOpen(f, false);
        else {
            f.closeIn = PICK_DELAY / 1000;
            syncAria(f);
        }
    }
    function move(f: F, to: number): void {
        f.hi = clamp(to, 0, f.opts.length - 1);
        syncAria(f);
    }
    function resetFields(): void {
        fields.forEach(function (f: F): void {
            f.sel = -1;
            f.hi = 0;
            setOpen(f, false);
        });
    }
    function relayout(): void {
        fields.forEach(syncAria);
    }
    function script(ts: number): void {
        const t = ts % 2000;
        if (lastT < 0) lastT = t;
        if (t < lastT) resetFields();
        EVENTS.forEach(function (e: [number, number, string, number]): void {
            if (e[0] <= lastT || e[0] > t) return;
            const f = fields[e[1]];
            if (e[2] === "open") setOpen(f, true);
            else if (e[2] === "hi") move(f, e[3]);
            else pick(f, e[3]);
        });
        lastT = t;
    }
    function step(dt: number, ts: number): void {
        fields.forEach(function (f: F): void {
            springStep(f.sp, f.open ? 1 : 0, CHEV_STIFF, CHEV_DAMP, dt);
            if (f.closeIn > 0) {
                f.closeIn -= dt;
                if (f.closeIn <= 0) setOpen(f, false);
            }
        });
    }
    function render(): void {
        fields.forEach(function (f: F): void {
            const x = f.sp.x;
            const o = clamp(x, 0, 1);
            const r = f.sel >= 0 ? Math.max(1, clamp(x, 0, 1.25)) : clamp(x, 0, 1.25);
            const s = 1 - (1 - LABEL_SCALE) * r;
            f.label.style.transform = "translate3d(0," + (-RISE_PX * r).toFixed(2) + "px,0) scale(" + s.toFixed(3) + ")";
            f.chev.style.transform = "rotate(" + (OPEN_DEG * x).toFixed(1) + "deg)";
            f.box.style.setProperty("--p", clamp(r, 0, 1).toFixed(3));
            const h = (OPT_H * f.opts.length + 2 * MENU_PAD) * o;
            f.menu.style.height = h.toFixed(1) + "px";
            f.menu.style.opacity = clamp(o * 1.6, 0, 1).toFixed(3);
            f.menu.style.visibility = h < 1 ? "hidden" : "visible";
        });
    }
    fields.forEach(function (f: F): void {
        f.opts.forEach(function (o: HTMLElement, k: number): void {
            on(o, "pointerenter", function (): void {
                if (f.open) move(f, k);
            });
            on(o, "click", function (): void {
                stopDemo();
                pick(f, k);
            });
        });
        // 목록을 누를 때 버튼이 포커스를 잃어 닫히지 않게 한다.
        on(f.menu, "mousedown", function (e: MouseEvent): void {
            e.preventDefault();
        });
        on(f.btn, "click", function (e: MouseEvent): void {
            stopDemo();
            if (e.detail === 0 && f.open) pick(f, f.hi);
            else setOpen(f, !f.open);
        });
        on(f.btn, "keydown", function (e: KeyboardEvent): void {
            if (e.key === "ArrowDown" || e.key === "ArrowUp") {
                e.preventDefault();
                stopDemo();
                if (!f.open) setOpen(f, true);
                else move(f, f.hi + (e.key === "ArrowDown" ? 1 : -1));
            } else if (e.key === "Escape" && f.open) {
                setOpen(f, false);
            }
        });
        on(f.btn, "blur", function (): void {
            if (f.open) setOpen(f, false);
        });
    });
    on(document, "pointerdown", function (e: PointerEvent): void {
        fields.forEach(function (f: F): void {
            if (f.open && !f.box.contains(e.target as Node)) setOpen(f, false);
        });
    });

    relayout();
    if (reduce) {
        render();
    } else {
        raf = requestAnimationFrame(frame);
    }

    return () => {
      cancelAnimationFrame(raf);
      offs.forEach((f) => f());
      ro.disconnect();
    };
  }, []);

  return (
    <main className={styles["stage"]}>
      <div ref={rootRef} className={styles["fl"] + " is-demo"} data-demo="1">
        <div className={styles["fl__field"]}>
          <div className={styles["fl__box"]} data-r="box">
            <button className={styles["fl__input"] + " " + styles["fl__select"]} id="c1" data-r="btn" type="button" role="combobox" aria-haspopup="listbox" aria-expanded="false" aria-controls="m1">
              <span className={styles["fl__val"]} data-r="val" />
            </button>
            <label className={styles["fl__label"]} htmlFor="c1" id="l1" data-r="label">도시</label>
            <svg className={styles["fl__chev"]} data-r="chev" aria-hidden="true" width="24" height="24" viewBox="0 0 256 256"><g fill="currentColor"><path d="m208 96l-80 80l-80-80Z" opacity=".2"/><path d="M215.39 92.94A8 8 0 0 0 208 88H48a8 8 0 0 0-5.66 13.66l80 80a8 8 0 0 0 11.32 0l80-80a8 8 0 0 0 1.73-8.72M128 164.69L67.31 104h121.38Z"/></g></svg>
            <ul className={styles["fl__menu"]} id="m1" role="listbox" aria-labelledby="l1" data-r="menu">
              <li className={styles["fl__opt"]} role="option" id="m1o0" data-r="opt" aria-selected="false">서울</li>
              <li className={styles["fl__opt"]} role="option" id="m1o1" data-r="opt" aria-selected="false">부산</li>
              <li className={styles["fl__opt"]} role="option" id="m1o2" data-r="opt" aria-selected="false">제주</li>
            </ul>
          </div>
        </div>
        <div className={styles["fl__field"]}>
          <div className={styles["fl__box"]} data-r="box">
            <button className={styles["fl__input"] + " " + styles["fl__select"]} id="c2" data-r="btn" type="button" role="combobox" aria-haspopup="listbox" aria-expanded="false" aria-controls="m2">
              <span className={styles["fl__val"]} data-r="val" />
            </button>
            <label className={styles["fl__label"]} htmlFor="c2" id="l2" data-r="label">요일</label>
            <svg className={styles["fl__chev"]} data-r="chev" aria-hidden="true" width="24" height="24" viewBox="0 0 256 256"><g fill="currentColor"><path d="m208 96l-80 80l-80-80Z" opacity=".2"/><path d="M215.39 92.94A8 8 0 0 0 208 88H48a8 8 0 0 0-5.66 13.66l80 80a8 8 0 0 0 11.32 0l80-80a8 8 0 0 0 1.73-8.72M128 164.69L67.31 104h121.38Z"/></g></svg>
            <ul className={styles["fl__menu"] + " " + styles["fl__menu--up"]} id="m2" role="listbox" aria-labelledby="l2" data-r="menu">
              <li className={styles["fl__opt"]} role="option" id="m2o0" data-r="opt" aria-selected="false">월요일</li>
              <li className={styles["fl__opt"]} role="option" id="m2o1" data-r="opt" aria-selected="false">수요일</li>
              <li className={styles["fl__opt"]} role="option" id="m2o2" data-r="opt" aria-selected="false">금요일</li>
            </ul>
          </div>
        </div>
      </div>
    </main>
  );
}