04クラス切替の状態遷移

<main class="stage">
  <div class="tg-panel is-demo">
    <div class="tg-panel__head">
      <span class="tg-panel__label">Shipping details</span>
      <span class="tg-panel__chevron">▾</span>
    </div>
    <div class="tg-panel__body">Arrives in 2–3 business days via standard mail.</div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-base;
$easing: $ease-spring;
$color: $subject-blue-light;   // 잉크 면 위 파란 글자 전용 토큰 — $subject-blue 는 4.03:1

@include stage($stage-paper);

.tg-panel {
  width: min(280px, 88vw);
  box-sizing: border-box;
  border-radius: $r-card;
  background: $subject-ink;
  color: $subject-cream;
  box-shadow: $shadow-raised;
  overflow: hidden;
  font-family: -apple-system, "Segoe UI", sans-serif;
}

.tg-panel__head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: $sp-4 $sp-4;
}

.tg-panel__label { font-weight: 600; font-size: 14px; line-height: 1; font-family: inherit; }

.tg-panel__chevron {
  display: inline-block;
  color: $color;
  transition: transform $duration $easing;
}

.tg-panel__body {
  padding: 0 $sp-4 $sp-4;
  font-weight: 400;
  font-size: 12px;
  line-height: 1.5;
  font-family: inherit;
  opacity: .85;
  transform-origin: top; // 규칙8: 패널 위변 scaleY 펼침
  transition: opacity $duration $easing, transform $duration $easing;
}

// 실사용 원리: isOpen 상태 하나가 className="is-open" 하나로 매핑되고, 사이 움직임은
// 전부 CSS transition 이 맡는다 (React state → class, class → motion).
.tg-panel:not(.is-open) .tg-panel__chevron { transform: rotate(-90deg); }
.tg-panel:not(.is-open) .tg-panel__body { opacity: 0; transform: scaleY(0); }

// 캡처용 루프: 닫힘 → 열림 → 닫힘을 2초에 걸쳐 반복
@keyframes tg-chevron { 0%, 15% { transform: rotate(-90deg); } 45%, 70% { transform: rotate(0deg); } 100% { transform: rotate(-90deg); } }
@keyframes tg-body    { 0%, 15% { opacity: 0; transform: scaleY(0); } 45%, 70% { opacity: .85; transform: scaleY(1); } 100% { opacity: 0; transform: scaleY(0); } }
.tg-panel.is-demo .tg-panel__chevron { animation: tg-chevron $dur-loop $easing infinite; }
.tg-panel.is-demo .tg-panel__body { animation: tg-body $dur-loop $easing infinite; }

@media (prefers-reduced-motion: reduce) {
  .tg-panel__chevron, .tg-panel__body { transition: none; }
  .tg-panel.is-demo .tg-panel__chevron,
  .tg-panel.is-demo .tg-panel__body { animation: none !important; opacity: .85; transform: none; }
}

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

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

.tg-panel {
  width: min(280px, 88vw);
  box-sizing: border-box;
  border-radius: 16px;
  background: #17141a;
  color: #fff7e6;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  overflow: hidden;
  font-family: -apple-system, "Segoe UI", sans-serif;
}

.tg-panel__head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px 16px;
}

.tg-panel__label {
  font-weight: 600;
  font-size: 14px;
  line-height: 1;
  font-family: inherit;
}

.tg-panel__chevron {
  display: inline-block;
  color: #5b8cf8;
  transition: transform 300ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.tg-panel__body {
  padding: 0 16px 16px;
  font-weight: 400;
  font-size: 12px;
  line-height: 1.5;
  font-family: inherit;
  opacity: 0.85;
  transform-origin: top;
  transition: opacity 300ms cubic-bezier(0.2, 0.8, 0.2, 1), transform 300ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.tg-panel:not(.is-open) .tg-panel__chevron {
  transform: rotate(-90deg);
}

.tg-panel:not(.is-open) .tg-panel__body {
  opacity: 0;
  transform: scaleY(0);
}

@keyframes tg-chevron {
  0%, 15% {
    transform: rotate(-90deg);
  }
  45%, 70% {
    transform: rotate(0deg);
  }
  100% {
    transform: rotate(-90deg);
  }
}
@keyframes tg-body {
  0%, 15% {
    opacity: 0;
    transform: scaleY(0);
  }
  45%, 70% {
    opacity: 0.85;
    transform: scaleY(1);
  }
  100% {
    opacity: 0;
    transform: scaleY(0);
  }
}
.tg-panel.is-demo .tg-panel__chevron {
  animation: tg-chevron 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

.tg-panel.is-demo .tg-panel__body {
  animation: tg-body 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@media (prefers-reduced-motion: reduce) {
  .tg-panel__chevron, .tg-panel__body {
    transition: none;
  }
  .tg-panel.is-demo .tg-panel__chevron,
  .tg-panel.is-demo .tg-panel__body {
    animation: none !important;
    opacity: 0.85;
    transform: none;
  }
}

import { CSSProperties, useState } from "react";
import styles from "./ToggleClassState.module.scss";

export interface ToggleClassStateProps {
  duration?: string;
  easing?: string;
}

export default function ToggleClassState({
  duration = "300ms",
  easing = "cubic-bezier(.2, .8, .2, 1)",
}: ToggleClassStateProps) {
  // The idiomatic React pattern: one boolean state maps straight onto one className.
  // Everything visual in between is CSS's job, not this component's.
  const [open, setOpen] = useState(false);

  const style: CSSProperties & { "--duration"?: string; "--easing"?: string } = {
    "--duration": duration,
    "--easing": easing,
  };

  return (
    <div className={`${styles.panel} ${open ? styles.open : ""}`} style={style}>
      <button className={styles.head} onClick={() => setOpen((v) => !v)}>
        <span className={styles.label}>Shipping details</span>
        <span className={styles.chevron}>▾</span>
      </button>
      <div className={styles.body}>Arrives in 2–3 business days via standard mail.</div>
    </div>
  );
}