07スクロールで隠れる

<main class="stage is-demo">
  <div class="layout">
    <nav class="rail" aria-label="目次">
      <a class="rail__link" href="#">概要</a>
      <a class="rail__link" href="#">インストール</a>
      <a class="rail__link" href="#">使い方</a>
      <a class="rail__link" href="#">トラブルシューティング</a>
    </nav>
    <div class="content" id="content">
      <p>このエリアを下にスクロールすると左のレールが退く。</p>
      <p>上にスクロールし直すとレールがすぐ戻る。</p>
      <p>本文が長いドキュメントで目次が画面を占領し続けないようにする。</p>
      <p>レールはウィンドウ全体ではなくこのコンテンツエリアのスクロールだけを見る。</p>
    </div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-quick;      // 220ms — 실제 스크롤 시 숨는 속도
$easing: $ease-out;
$color: $subject-cream;     // 레일 링크 강조색

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

.layout {
  display: flex;
  width: min(90vw, 340px);
  height: min(50vw, 150px);
  border-radius: $r-card;
  overflow: hidden;
  background: $stage-paper;
  box-shadow: $shadow-raised;
}

.rail {
  flex: none;
  width: 96px;
  box-sizing: border-box;
  display: flex; flex-direction: column; gap: $sp-1;
  padding: $sp-3 $sp-2;
  background: $stage-ink;
  transform: translateX(0);
  transition: transform $duration $easing;
}
.rail__link {
  padding: $sp-1 $sp-2;
  border-radius: $r-xs;
  color: $stage-paper; text-decoration: none; font-weight: 500; font-size: 11px; line-height: 1.2; font-family: inherit;
  &:hover, &:focus-visible { color: $color; background: rgba($stage-paper, .12); }
}
.rail.is-hidden { transform: translateX(-100%); }

.content {
  flex: 1;
  overflow-y: auto;
  box-sizing: border-box;
  padding: $sp-3;
  display: flex; flex-direction: column; gap: $sp-4;
  color: $stage-ink;

  p { margin: 0; font-size: clamp(10px, 3vmin, 12px); line-height: 1.5; opacity: .8; }
}

// 데모 루프: 레일이 나갔다 들어왔다를 2초에 한 바퀴(실제 스크롤 여부와 무관)
.stage.is-demo .rail { animation: rail-loop $dur-loop ease-in-out infinite; }

@keyframes rail-loop {
  0%, 100% { transform: translateX(0); }
  40%, 70% { transform: translateX(-100%); }
}

@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .rail { animation: none; }
  .rail { transition-duration: 1ms; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.layout {
  display: flex;
  width: min(90vw, 340px);
  height: min(50vw, 150px);
  border-radius: 16px;
  overflow: hidden;
  background: #ffffff;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.rail {
  flex: none;
  width: 96px;
  box-sizing: border-box;
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 12px 8px;
  background: #17141a;
  transform: translateX(0);
  transition: transform 220ms ease-out;
}

.rail__link {
  padding: 4px 8px;
  border-radius: 4px;
  color: #ffffff;
  text-decoration: none;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.2;
  font-family: inherit;
}
.rail__link:hover, .rail__link:focus-visible {
  color: #fff7e6;
  background: rgba(255, 255, 255, 0.12);
}

.rail.is-hidden {
  transform: translateX(-100%);
}

.content {
  flex: 1;
  overflow-y: auto;
  box-sizing: border-box;
  padding: 12px;
  display: flex;
  flex-direction: column;
  gap: 16px;
  color: #17141a;
}
.content p {
  margin: 0;
  font-size: clamp(10px, 3vmin, 12px);
  line-height: 1.5;
  opacity: 0.8;
}

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

@keyframes rail-loop {
  0%, 100% {
    transform: translateX(0);
  }
  40%, 70% {
    transform: translateX(-100%);
  }
}
@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .rail {
    animation: none;
  }
  .rail {
    transition-duration: 1ms;
  }
}

// 콘텐츠 스크롤 방향을 비교해 레일을 translateX 로 숨기고 보인다. 실제 스크롤이 오면 데모 루프를 넘긴다.
(function () {
  var stage = document.querySelector('.stage');
  var rail = document.querySelector('.rail');
  var content = document.getElementById('content');
  var last = 0;
  content.addEventListener('scroll', function () {
    stage.classList.remove('is-demo');
    var y = content.scrollTop;
    if (y > last + 4) rail.classList.add('is-hidden');
    else if (y < last - 4) rail.classList.remove('is-hidden');
    last = y;
  });
})();

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

type ScrollEv = { currentTarget: HTMLDivElement };

export type ScrollHideRailProps = {
  duration?: number;
  easing?: string;
  color?: string;
};

const LINKS = ["개요", "설치", "사용법", "문제 해결"];

export default function ScrollHideRail({
  duration = 220,
  easing = "ease-out",
  color = "#fff7e6",
}: ScrollHideRailProps) {
  const [hidden, setHidden] = useState(false);
  const lastY = useRef(0);

  function onScroll(e: ScrollEv) {
    const y = e.currentTarget.scrollTop;
    const last = lastY.current ?? 0;
    if (y > last + 4) setHidden(true);
    else if (y < last - 4) setHidden(false);
    lastY.current = y;
  }

  const vars: CSSProperties = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  return (
    <div className={styles.stage} style={vars}>
      <div className={styles.layout}>
        <nav className={styles.rail} data-hidden={hidden} aria-label="목차">
          {LINKS.map((label) => (
            <a key={label} className={styles.link} href="#">{label}</a>
          ))}
        </nav>
        <div className={styles.content} onScroll={onScroll}>
          <p>이 영역을 아래로 스크롤하면 왼쪽 레일이 비켜난다.</p>
          <p>다시 위로 스크롤하면 레일이 즉시 돌아온다.</p>
          <p>본문이 긴 문서에서 목차가 화면을 계속 차지하지 않게 한다.</p>
          <p>레일은 창 전체가 아니라 이 콘텐츠 영역의 스크롤만 본다.</p>
        </div>
      </div>
    </div>
  );
}