08light-dark() aware glow

<main class="stage is-demo">
  <div class="row" aria-hidden="true">
    <div class="pane pane--light"><span class="badge"></span></div>
    <div class="pane pane--dark"><span class="badge"></span></div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;   // 2s — 숨쉬기 한 번
$easing: ease-in-out;
$color: #7c5cff;        // 네온 인디고

@include stage($stage-ink);

.row { display: flex; gap: $sp-6; }

.pane {
  box-sizing: border-box;
  width: clamp(96px, 26vmin, 130px);
  aspect-ratio: 1;
  border-radius: $r-card;
  display: grid; place-items: center;
}

// color-scheme 은 요소 단위로도 걸린다 — light-dark() 는 이 값을 보고 고른다
.pane--light { background: $stage-paper; color-scheme: light; }
.pane--dark  { background: $stage-ink;   color-scheme: dark;  border: 1px solid rgba($stage-paper, .1); }

.badge {
  width: 42px; height: 42px; border-radius: 50%;
  background: light-dark(#e9e2ff, #1c1630);
  // light-dark() 는 색 값에만 쓴다 — 길이(px)에 쓰면 무효한 선언이라 box-shadow 전체가 버려진다 (함정 섹션 재료, 실측)
  --glow-rest: #{light-dark(rgba($color, 0), rgba($color, .2))};
  --glow-peak: #{light-dark(rgba($color, .7), $color)};
  --glow-peak-soft: #{light-dark(rgba($color, .3), rgba($color, .7))};
  // 미디어쿼리 없이 한 줄이 배경에 맞춰 옅게/짙게 갈린다
  box-shadow: 0 0 $sp-1 var(--glow-rest);
}

// box-shadow 가 거의 안 보이는 상태와 짙은 상태를 짧게 오간다 — 전환을 좁게 몰아야 눈에 확실히 띈다
.stage.is-demo .badge {
  animation: breathe $duration $easing infinite;
}

@keyframes breathe {
  0%, 15%, 85%, 100% { box-shadow: 0 0 $sp-1 var(--glow-rest); }
  35%, 65%            { box-shadow: 0 0 $sp-4 var(--glow-peak), 0 0 $sp-10 var(--glow-peak-soft); }
}

@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .badge { animation: none; }
}

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);
}

.row {
  display: flex;
  gap: 24px;
}

.pane {
  box-sizing: border-box;
  width: clamp(96px, 26vmin, 130px);
  aspect-ratio: 1;
  border-radius: 16px;
  display: grid;
  place-items: center;
}

.pane--light {
  background: #ffffff;
  color-scheme: light;
}

.pane--dark {
  background: #17141a;
  color-scheme: dark;
  border: 1px solid rgba(255, 255, 255, 0.1);
}

.badge {
  width: 42px;
  height: 42px;
  border-radius: 50%;
  background: light-dark(#e9e2ff, #1c1630);
  --glow-rest: light-dark(rgba(124, 92, 255, 0), rgba(124, 92, 255, 0.2));
  --glow-peak: light-dark(rgba(124, 92, 255, 0.7), #7c5cff);
  --glow-peak-soft: light-dark(rgba(124, 92, 255, 0.3), rgba(124, 92, 255, 0.7));
  box-shadow: 0 0 4px var(--glow-rest);
}

.stage.is-demo .badge {
  animation: breathe 2s ease-in-out infinite;
}

@keyframes breathe {
  0%, 15%, 85%, 100% {
    box-shadow: 0 0 4px var(--glow-rest);
  }
  35%, 65% {
    box-shadow: 0 0 16px var(--glow-peak), 0 0 40px var(--glow-peak-soft);
  }
}
@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .badge {
    animation: none;
  }
}

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

export type LightDarkGlowProps = {
  /** 숨쉬기 한 번 (기본 2000ms) */
  duration?: number;
  color?: string;
};

export default function LightDarkGlow({ duration = 2000, color = "#7c5cff" }: LightDarkGlowProps) {
  const vars: CSSProperties = { "--duration": `${duration}ms`, "--color": color } as CSSProperties;
  return (
    <div className={styles.row} style={vars}>
      <div className={`${styles.pane} ${styles.light}`}>
        <span className={styles.badge} />
      </div>
      <div className={`${styles.pane} ${styles.dark}`}>
        <span className={styles.badge} />
      </div>
    </div>
  );
}