08Negative invert flash

<main class="stage">
  <p class="ni-wrap is-demo">
    <span class="ni-base">EXPOSED</span>
    <span class="ni-negative" aria-hidden="true">EXPOSED</span>
  </p>
</main>

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

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

@include stage($stage-paper);

.ni-wrap {
  position: relative;
  margin: 0;
  display: inline-block;
}

.ni-base,
.ni-negative {
  display: block;
  font: 800 clamp(20px, 6vw, 30px)/1.2 "Space Mono", "Courier New", monospace;
  letter-spacing: .02em;
}

.ni-base { color: $color; }

.ni-negative {
  position: absolute;
  inset: 0;
  color: $stage-paper;
  background: $color;
  padding: $sp-1 $sp-2;
  margin: -#{$sp-1} -#{$sp-2};
  border-radius: $r-xs;
}

// 데모 루프: 색이 반전된 네거티브 레이어가 두세 번 깜빡이다 사라지고 정상 색 글자만 남는다
@keyframes ni-flash {
  0%, 4% { opacity: 1; }
  9% { opacity: 0; }
  14% { opacity: 1; }
  19% { opacity: 0; }
  24% { opacity: 1; }
  32%, 100% { opacity: 0; }
}

.ni-wrap.is-demo .ni-negative { animation: ni-flash $duration $easing infinite; }

@media (prefers-reduced-motion: reduce) {
  .ni-negative,
  .ni-wrap.is-demo .ni-negative {
    animation: none !important;
    opacity: 0 !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);
}

.ni-wrap {
  position: relative;
  margin: 0;
  display: inline-block;
}

.ni-base,
.ni-negative {
  display: block;
  font: 800 clamp(20px, 6vw, 30px)/1.2 "Space Mono", "Courier New", monospace;
  letter-spacing: 0.02em;
}

.ni-base {
  color: #2f6df6;
}

.ni-negative {
  position: absolute;
  inset: 0;
  color: #ffffff;
  background: #2f6df6;
  padding: 4px 8px;
  margin: -4px -8px;
  border-radius: 4px;
}

@keyframes ni-flash {
  0%, 4% {
    opacity: 1;
  }
  9% {
    opacity: 0;
  }
  14% {
    opacity: 1;
  }
  19% {
    opacity: 0;
  }
  24% {
    opacity: 1;
  }
  32%, 100% {
    opacity: 0;
  }
}
.ni-wrap.is-demo .ni-negative {
  animation: ni-flash 2s ease-out infinite;
}

@media (prefers-reduced-motion: reduce) {
  .ni-negative,
  .ni-wrap.is-demo .ni-negative {
    animation: none !important;
    opacity: 0 !important;
  }
}

import { CSSProperties, useEffect, useRef, useState } from "react";
import styles from "./NegativeInvertFlash.module.scss";

export interface NegativeInvertFlashProps {
  text?: string;
  duration?: string;
  easing?: string;
}

// 실사용: 뷰포트에 들어오면 색이 반전된 레이어가 두세 번 깜빡이다 사라지고 정상 색 글자만 남는다.
export default function NegativeInvertFlash({
  text = "EXPOSED",
  duration = "160ms",
  easing = "ease-out",
}: NegativeInvertFlashProps) {
  const ref = useRef<HTMLParagraphElement>(null);
  const [flash, setFlash] = useState(0);

  useEffect(() => {
    const el = ref.current;
    if (!el) return;
    const io = new IntersectionObserver((entries) => {
      entries.forEach((e) => {
        if (!e.isIntersecting) return;
        io.unobserve(e.target);
        const reduced = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
        if (reduced) return;
        const steps = [1, 0, 1, 0, 1, 0];
        steps.forEach((v, i) => setTimeout(() => setFlash(v), i * 160));
      });
    }, { threshold: 0.3 });
    io.observe(el);
    return () => io.disconnect();
  }, []);

  const style = { "--duration": duration, "--easing": easing } as CSSProperties;

  return (
    <p className={styles.wrap} style={style} ref={ref}>
      <span className={styles.base}>{text}</span>
      <span className={styles.negative} style={{ opacity: flash }} aria-hidden="true">{text}</span>
    </p>
  );
}