09ライト・ダーク・自動の3段階

<main class="stage">
  <div class="panel">
    <p class="panel__title">環境設定</p>
    <div class="segmented">
      <span class="segmented__slot segmented__slot--light"></span>
      <span class="segmented__slot segmented__slot--dark"></span>
      <span class="segmented__slot segmented__slot--auto"></span>
      <span class="segmented__thumb"></span>
    </div>
  </div>
</main>

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

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

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

.panel {
  position: relative;
  width: clamp(200px, 70vw, 260px); height: clamp(120px, 42vw, 150px);
  border-radius: $r-card; box-shadow: $shadow-raised;
  background: $subject-cream; color: $subject-ink;
  box-sizing: border-box; padding: clamp(14px, 5vw, 20px);
  display: flex; flex-direction: column; justify-content: center; gap: clamp(12px, 4vw, 18px);
}
.panel__title { margin: 0; font-weight: 700; font-size: clamp(12px, 3.6vw, 15px); line-height: 1.3; font-family: inherit; }

// 3칸짜리 트랙 위 인디케이터가 라이트→다크→자동 순으로 이동한다. transform: translateX 만 쓴다.
.segmented {
  position: relative; display: flex; width: 96px; height: 28px;
  border-radius: $r-pill; background: rgba(23, 20, 26, .08); overflow: hidden;
}
.segmented__slot { flex: 1; }
.segmented__thumb {
  position: absolute; top: 3px; left: 3px; width: 26px; height: 22px; border-radius: $r-pill;
  background: $color; box-shadow: $shadow-press;
  transform: translateX(0); animation: thumb-move $dur-loop $easing infinite;
}

@keyframes thumb-move {
  0%, 22%  { transform: translateX(0); }
  33%, 55% { transform: translateX(32px); }
  66%, 88% { transform: translateX(64px); }
  100%     { transform: translateX(0); }
}

// ── 접근성: 움직임 줄이기 설정이면 첫 칸(라이트)에 고정 ──────────
@media (prefers-reduced-motion: reduce) {
  .segmented__thumb { animation: none !important; transform: translateX(0); }
}

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);
}

.panel {
  position: relative;
  width: clamp(200px, 70vw, 260px);
  height: clamp(120px, 42vw, 150px);
  border-radius: 16px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  background: #fff7e6;
  color: #17141a;
  box-sizing: border-box;
  padding: clamp(14px, 5vw, 20px);
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: clamp(12px, 4vw, 18px);
}

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

.segmented {
  position: relative;
  display: flex;
  width: 96px;
  height: 28px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.08);
  overflow: hidden;
}

.segmented__slot {
  flex: 1;
}

.segmented__thumb {
  position: absolute;
  top: 3px;
  left: 3px;
  width: 26px;
  height: 22px;
  border-radius: 999px;
  background: #2f6df6;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  transform: translateX(0);
  animation: thumb-move 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@keyframes thumb-move {
  0%, 22% {
    transform: translateX(0);
  }
  33%, 55% {
    transform: translateX(32px);
  }
  66%, 88% {
    transform: translateX(64px);
  }
  100% {
    transform: translateX(0);
  }
}
@media (prefers-reduced-motion: reduce) {
  .segmented__thumb {
    animation: none !important;
    transform: translateX(0);
  }
}

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

export type ThreeStateMode = "light" | "dark" | "auto";

export type ThreeStateToggleProps = {
  mode: ThreeStateMode;
  onChange?: (mode: ThreeStateMode) => void;
  /** 인디케이터가 옮겨가는 시간 (기본 350ms) */
  duration?: number;
  easing?: string;
  color?: string;
  className?: string;
};

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

const MODES: ThreeStateMode[] = ["light", "dark", "auto"];

export default function ThreeStateToggle({
  mode,
  onChange,
  duration = 350,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#2f6df6",
  className = "",
}: ThreeStateToggleProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  return (
    <span className={`${styles.track} ${className}`} style={vars} data-mode={mode} role="radiogroup" aria-label="환경설정">
      {MODES.map((m) => (
        <button
          key={m}
          type="button"
          className={styles.slot}
          role="radio"
          aria-checked={m === mode}
          onClick={() => onChange?.(m)}
        />
      ))}
      <span className={styles.thumb} />
    </span>
  );
}