02Header nhóm cố định

<main class="stage">
  <div class="grp-wrap is-demo" tabindex="0" aria-label="Danh sách liên hệ. Cuộn bằng phím mũi tên hoặc kéo">
    <ul class="grp-list">
      <li class="grp-group">
        <div class="grp-group__header">A</div>
        <ul class="grp-group__rows">
          <li>Ari</li><li>Aiden</li><li>Ava</li>
        </ul>
      </li>
      <li class="grp-group">
        <div class="grp-group__header">B</div>
        <ul class="grp-group__rows">
          <li>Bella</li><li>Ben</li><li>Bora</li>
        </ul>
      </li>
      <li class="grp-group">
        <div class="grp-group__header">C</div>
        <ul class="grp-group__rows">
          <li>Chloe</li><li>Charlie</li><li>Cyan</li>
        </ul>
      </li>
    </ul>
  </div>
</main>

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

$duration: $dur-base;                                  // 스크롤 자동 시연 왕복 시간(스크립트 값과 맞춤)
$easing: $ease-out;
$color: $subject-pink;                                 // 그룹 헤더 배경 (파스텔)

@include stage($stage-paper);

.grp-wrap {
  width: 220px;
  height: 168px;
  overflow: auto;
  border-radius: $r-card;
  background: $stage-paper;
  box-shadow: $shadow-raised;
}
.grp-wrap:focus-visible { outline: 2px solid $subject-blue; outline-offset: 2px; }

.grp-list { list-style: none; margin: 0; padding: 0; }
.grp-group { margin: 0; padding: 0; }

.grp-group__header {
  position: sticky;
  top: 0;
  z-index: 1;
  padding: $sp-2 $sp-4;
  font-weight: 700;
  font-size: 13px;
  color: $stage-ink;
  background: $color;
}
.grp-group:nth-of-type(2) .grp-group__header { background: $subject-mint; }
.grp-group:nth-of-type(3) .grp-group__header { background: $subject-lilac; }

.grp-group__rows {
  list-style: none;
  margin: 0;
  padding: 0;
}
.grp-group__rows li {
  padding: $sp-2 $sp-4;
  font-size: 13px;
  color: $stage-ink;
  border-bottom: 1px solid rgba(23, 20, 26, .06);
}

@media (prefers-reduced-motion: reduce) {
  .grp-wrap { scroll-behavior: auto; }
}

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);
}

.grp-wrap {
  width: 220px;
  height: 168px;
  overflow: auto;
  border-radius: 16px;
  background: #ffffff;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}

.grp-wrap:focus-visible {
  outline: 2px solid #2f6df6;
  outline-offset: 2px;
}

.grp-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.grp-group {
  margin: 0;
  padding: 0;
}

.grp-group__header {
  position: sticky;
  top: 0;
  z-index: 1;
  padding: 8px 16px;
  font-weight: 700;
  font-size: 13px;
  color: #17141a;
  background: #ff9ebb;
}

.grp-group:nth-of-type(2) .grp-group__header {
  background: #4cd4a6;
}

.grp-group:nth-of-type(3) .grp-group__header {
  background: #b9a0ff;
}

.grp-group__rows {
  list-style: none;
  margin: 0;
  padding: 0;
}

.grp-group__rows li {
  padding: 8px 16px;
  font-size: 13px;
  color: #17141a;
  border-bottom: 1px solid rgba(23, 20, 26, 0.06);
}

@media (prefers-reduced-motion: reduce) {
  .grp-wrap {
    scroll-behavior: auto;
  }
}

(function () {
  var wrap = document.querySelector('.grp-wrap');
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var raf = null, t0 = null;
  function maxY() { return wrap.scrollHeight - wrap.clientHeight; }
  function loop(ts) {
    if (!wrap.classList.contains('is-demo')) return;
    if (t0 === null) t0 = ts;
    var p = ((ts - t0) / 2000) % 1;
    var s = p < .5 ? p * 2 : 2 - p * 2;
    wrap.scrollTop = s * maxY();
    raf = requestAnimationFrame(loop);
  }
  function stop() {
    wrap.classList.remove('is-demo');
    if (raf) cancelAnimationFrame(raf);
  }
  wrap.addEventListener('pointerdown', stop);
  wrap.addEventListener('wheel', stop, { passive: true });
  wrap.addEventListener('keydown', function (e) {
    var step = 24;
    if (e.key === 'ArrowDown') { stop(); wrap.scrollTop += step; }
    else if (e.key === 'ArrowUp') { stop(); wrap.scrollTop -= step; }
    else return;
    e.preventDefault();
  });
  if (!reduce) requestAnimationFrame(loop);
})();

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

export type Group = { letter: string; names: string[] };

export type GroupedHeaderStickySectionProps = {
  groups: Group[];
  /** 스크롤 이징 (기본 300ms) */
  duration?: number;
  easing?: string;
  /** 첫 그룹 헤더 배경(파스텔) */
  color?: string;
};

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

/** 그룹 헤더가 position:sticky 로 스크롤 중 위에 붙어 있다가 다음 그룹이 밀어 올린다 */
export default function GroupedHeaderStickySection({
  groups,
  duration = 300,
  easing = "ease-out",
  color = "#ff9ebb",
}: GroupedHeaderStickySectionProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  return (
    <div className={styles.wrap} style={vars} tabIndex={0} aria-label="연락처 목록">
      <ul className={styles.list}>
        {groups.map((g, i) => (
          <li key={g.letter} className={styles.group}>
            <div className={styles.header} data-i={i % 3}>{g.letter}</div>
            <ul className={styles.rows}>
              {g.names.map((n) => <li key={n}>{n}</li>)}
            </ul>
          </li>
        ))}
      </ul>
    </div>
  );
}