07カスタムセレクトが開く

<main class="stage">
  <div class="cs is-demo">
    <button type="button" class="cs__btn" aria-haspopup="listbox" aria-expanded="false" id="cs-btn">
      <span class="cs__value">テーマを選択</span>
      <svg class="cs__chevron" viewBox="0 0 24 24" aria-hidden="true"><polyline points="6 9 12 15 18 9"/></svg>
    </button>
    <ul class="cs__list" role="listbox" aria-labelledby="cs-btn">
      <li role="option" class="cs__opt">ライト</li>
      <li role="option" class="cs__opt">ダーク</li>
      <li role="option" class="cs__opt">システム</li>
    </ul>
    <span class="cs__bloom" aria-hidden="true"></span>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-base;                  // 열리고 닫히는 시간
$easing: cubic-bezier(.3, 1.5, .4, 1); // 스프링 오버슛 — 목록 scaleY 가 1 을 지나 1.06 까지 뻗었다가 감아 들어간다
$color: $subject-ink;                  // 셰브론 색 — 주황 무대 위 전경은 잉크(크림은 3.11:1 미달)

@include stage($stage-orange);

.cs { position: relative; width: min(200px, 78vw); }
.cs__btn {
  display: flex; align-items: center; justify-content: space-between;
  width: 100%;
  border: 2px solid rgba($subject-ink, .4);
  border-radius: $r-control;
  padding: $sp-3 $sp-4;
  font-weight: 600;
  font-size: clamp(13px, 3.8vw, 15px);
  line-height: 1;
  font-family: inherit;
  color: $subject-ink;                  // 주황 면 위 크림 글자는 3.11:1 — 잉크로 5.50:1
  background: transparent;
  cursor: pointer;
}
.cs__chevron {
  width: 16px; height: 16px;
  fill: none; stroke: $color; stroke-width: 2;
  stroke-linecap: round; stroke-linejoin: round;
  transform: rotate(0deg);
  transition: transform $duration $easing;
}
.cs.is-open .cs__chevron { transform: rotate(180deg); }

.cs__list {
  position: absolute;
  left: 0; right: 0; top: calc(100% + $sp-2);
  margin: 0; padding: $sp-2;
  list-style: none;
  border-radius: $r-control;
  background: $subject-cream;
  box-shadow: $shadow-raised;
  transform: scaleY(0);
  transform-origin: top; // 규칙8: 버튼 아래변에서 펼침
  opacity: 0;
  pointer-events: none;
  transition: transform $duration $easing, opacity $duration $easing;
}
.cs.is-open .cs__list { transform: scaleY(1); opacity: 1; pointer-events: auto; }

// 목록이 열리는 순간 버튼 중심에서 아래로 번지는 radial 글로우 확산 한 겹
.cs__bloom {
  position: absolute;
  left: 0; right: 0; top: calc(100% + $sp-2);
  height: 48px;
  background: radial-gradient(ellipse 70% 100% at 50% 0%, rgba($subject-cream, .35) 0%, rgba($subject-cream, 0) 70%);
  opacity: 0;
  pointer-events: none;
}
.cs.is-open .cs__bloom { animation: cs-bloom $dur-base $ease-out; }

@keyframes cs-bloom {
  0%   { opacity: 0; transform: scaleY(.5); }
  40%  { opacity: 1; transform: scaleY(1); }
  100% { opacity: 0; transform: scaleY(1.1); }
}

.cs__opt {
  padding: $sp-2 $sp-3;
  border-radius: $r-sm;
  font-weight: 500;
  font-size: clamp(13px, 3.6vw, 14px);
  line-height: 1;
  font-family: inherit;
  color: $subject-orange-deep;         // 크림 면 위 주황 글자는 3.11:1 — deep 으로 5.04:1

  &:hover { background: rgba($stage-orange, .08); }
}

@media (prefers-reduced-motion: reduce) {
  .cs__chevron, .cs__list { transition: none; }
  .cs.is-open .cs__bloom { animation: none; }
}

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);
}

.cs {
  position: relative;
  width: min(200px, 78vw);
}

.cs__btn {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  border: 2px solid rgba(23, 20, 26, 0.4);
  border-radius: 12px;
  padding: 12px 16px;
  font-weight: 600;
  font-size: clamp(13px, 3.8vw, 15px);
  line-height: 1;
  font-family: inherit;
  color: #17141a;
  background: transparent;
  cursor: pointer;
}

.cs__chevron {
  width: 16px;
  height: 16px;
  fill: none;
  stroke: #17141a;
  stroke-width: 2;
  stroke-linecap: round;
  stroke-linejoin: round;
  transform: rotate(0deg);
  transition: transform 300ms cubic-bezier(0.3, 1.5, 0.4, 1);
}

.cs.is-open .cs__chevron {
  transform: rotate(180deg);
}

.cs__list {
  position: absolute;
  left: 0;
  right: 0;
  top: calc(100% + 8px);
  margin: 0;
  padding: 8px;
  list-style: none;
  border-radius: 12px;
  background: #fff7e6;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  transform: scaleY(0);
  transform-origin: top;
  opacity: 0;
  pointer-events: none;
  transition: transform 300ms cubic-bezier(0.3, 1.5, 0.4, 1), opacity 300ms cubic-bezier(0.3, 1.5, 0.4, 1);
}

.cs.is-open .cs__list {
  transform: scaleY(1);
  opacity: 1;
  pointer-events: auto;
}

.cs__bloom {
  position: absolute;
  left: 0;
  right: 0;
  top: calc(100% + 8px);
  height: 48px;
  background: radial-gradient(ellipse 70% 100% at 50% 0%, rgba(255, 247, 230, 0.35) 0%, rgba(255, 247, 230, 0) 70%);
  opacity: 0;
  pointer-events: none;
}

.cs.is-open .cs__bloom {
  animation: cs-bloom 300ms ease-out;
}

@keyframes cs-bloom {
  0% {
    opacity: 0;
    transform: scaleY(0.5);
  }
  40% {
    opacity: 1;
    transform: scaleY(1);
  }
  100% {
    opacity: 0;
    transform: scaleY(1.1);
  }
}
.cs__opt {
  padding: 8px 12px;
  border-radius: 8px;
  font-weight: 500;
  font-size: clamp(13px, 3.6vw, 14px);
  line-height: 1;
  font-family: inherit;
  color: #c93000;
}
.cs__opt:hover {
  background: rgba(255, 77, 31, 0.08);
}

@media (prefers-reduced-motion: reduce) {
  .cs__chevron, .cs__list {
    transition: none;
  }
  .cs.is-open .cs__bloom {
    animation: none;
  }
}

// 실사용: 버튼 클릭으로 연다·닫는다. 데모(.is-demo)는 같은 클래스를 주기적으로 토글 (5줄)
var cs = document.querySelector('.cs');
var btn = cs.querySelector('.cs__btn');
var toggle = function () { cs.classList.toggle('is-open'); btn.setAttribute('aria-expanded', cs.classList.contains('is-open')); };
btn.addEventListener('click', toggle);
if (cs.classList.contains('is-demo')) setInterval(toggle, 500);

import { useState } from "react";
import type { CSSProperties } from "react";
import styles from "./CustomSelectOpen.module.scss";

export type CustomSelectOpenProps = {
  id?: string;
  label?: string;
  options?: string[];
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };

export default function CustomSelectOpen({
  id = "cs-btn",
  label = "Choose theme",
  options = ["Light", "Dark", "System"],
  duration = 220,
  easing = "cubic-bezier(.3,1.5,.4,1)",
  color = "#17141a",
}: CustomSelectOpenProps) {
  const [open, setOpen] = useState(false);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  return (
    <div className={open ? `${styles.cs} ${styles.open}` : styles.cs} style={vars}>
      <button
        type="button"
        id={id}
        className={styles.btn}
        aria-haspopup="listbox"
        aria-expanded={open}
        onClick={() => setOpen((v) => !v)}
      >
        <span>{label}</span>
        <svg className={styles.chevron} viewBox="0 0 24 24" aria-hidden="true"><polyline points="6 9 12 15 18 9" /></svg>
      </button>
      <ul className={styles.list} role="listbox" aria-labelledby={id}>
        {options.map((opt) => (
          <li key={opt} role="option" className={styles.opt}>{opt}</li>
        ))}
      </ul>
      <span className={styles.bloom} aria-hidden="true" />
    </div>
  );
}