08全体の色がフェード切替

<main class="stage">
  <div class="panel">
    <div class="panel__face panel__face--light">
      <p class="panel__title">ドキュメント</p>
      <p class="panel__line"></p>
      <p class="panel__line panel__line--short"></p>
    </div>
    <div class="panel__face panel__face--dark">
      <p class="panel__title">ドキュメント</p>
      <p class="panel__line"></p>
      <p class="panel__line panel__line--short"></p>
    </div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────
$duration: $dur-enter;
$easing: $ease-out;
$color: $subject-blue;

// ── 데모 무대 ───────────────────────────────
@include stage($stage-paper);

.panel {
  position: relative; overflow: hidden;
  width: clamp(200px, 70vw, 260px); height: clamp(120px, 42vw, 150px);
  border-radius: $r-card; box-shadow: $shadow-raised;
}
.panel__face {
  position: absolute; inset: 0; box-sizing: border-box;
  padding: clamp(12px, 5vw, 18px); text-align: left;
}
.panel__face--light {
  background: $subject-cream; color: $subject-ink;
  opacity: 1; animation: face-light $dur-loop $easing infinite;
}
.panel__face--dark {
  background: $stage-ink; color: $subject-cream;
  opacity: 0; animation: face-dark $dur-loop $easing infinite;
}
.panel__title { margin: 0 0 6px; font-weight: 700; font-size: clamp(12px, 3.6vw, 15px); line-height: 1.3; font-family: inherit; }
.panel__line { margin: 0 0 6px; width: 70%; height: 8px; border-radius: 4px; background: currentColor; opacity: .25; }
.panel__line--short { width: 40%; }

// 배경과 글자색이 같은 곡선을 따라 함께 뒤바뀐다. 토글 없이 페이지 전체가 페이드한다
@keyframes face-light { 0%, 15% { opacity: 1; } 40%, 60% { opacity: 0; } 85%, 100% { opacity: 1; } }
@keyframes face-dark  { 0%, 15% { opacity: 0; } 40%, 60% { opacity: 1; } 85%, 100% { opacity: 0; } }

// ── 접근성: 움직임 줄이기 설정이면 라이트 상태로 고정 ──────────
@media (prefers-reduced-motion: reduce) {
  .panel__face--light, .panel__face--dark { animation: none !important; }
}

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);
}

.panel {
  position: relative;
  overflow: hidden;
  width: clamp(200px, 70vw, 260px);
  height: clamp(120px, 42vw, 150px);
  border-radius: 16px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.panel__face {
  position: absolute;
  inset: 0;
  box-sizing: border-box;
  padding: clamp(12px, 5vw, 18px);
  text-align: left;
}

.panel__face--light {
  background: #fff7e6;
  color: #17141a;
  opacity: 1;
  animation: face-light 2s ease-out infinite;
}

.panel__face--dark {
  background: #17141a;
  color: #fff7e6;
  opacity: 0;
  animation: face-dark 2s ease-out infinite;
}

.panel__title {
  margin: 0 0 6px;
  font-weight: 700;
  font-size: clamp(12px, 3.6vw, 15px);
  line-height: 1.3;
  font-family: inherit;
}

.panel__line {
  margin: 0 0 6px;
  width: 70%;
  height: 8px;
  border-radius: 4px;
  background: currentColor;
  opacity: 0.25;
}

.panel__line--short {
  width: 40%;
}

@keyframes face-light {
  0%, 15% {
    opacity: 1;
  }
  40%, 60% {
    opacity: 0;
  }
  85%, 100% {
    opacity: 1;
  }
}
@keyframes face-dark {
  0%, 15% {
    opacity: 0;
  }
  40%, 60% {
    opacity: 1;
  }
  85%, 100% {
    opacity: 0;
  }
}
@media (prefers-reduced-motion: reduce) {
  .panel__face--light, .panel__face--dark {
    animation: none !important;
  }
}

import type { CSSProperties, ReactNode } from "react";
import styles from "./ColorFadeToggle.module.scss";

export type ColorFadeToggleProps = {
  dark: boolean;
  /** 전체 페이드가 끝나는 시간 (기본 800ms) */
  duration?: number;
  easing?: string;
  lightContent: ReactNode;
  darkContent: ReactNode;
  className?: string;
};

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

export default function ColorFadeToggle({
  dark,
  duration = 800,
  easing = "ease-out",
  lightContent,
  darkContent,
  className = "",
}: ColorFadeToggleProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing };
  return (
    <div className={`${styles.panel} ${className}`} style={vars} data-dark={dark}>
      <div className={styles.light}>{lightContent}</div>
      <div className={styles.dark}>{darkContent}</div>
    </div>
  );
}