07Sticky + parallax combo

<main class="stage is-demo">
  <div class="stickypar">
    <div class="stickypar__bg" aria-hidden="true"></div>
    <p class="stickypar__caption">A caption that stays put</p>
  </div>
</main>

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

// ── 변수 3개. 변형은 이것만 바꾼다 ──────────────────────────
$bg-shift: 40px;                                 // 뒤 배경 이동량
$duration: $dur-loop;                            // 데모 왕복 주기
$color: $subject-cream;                          // 배경 결·문장 글자 색 (orange 무대라 cream)

@include stage($stage-orange);

.stickypar {
  position: relative;
  width: 100%;
  height: 100%;
  overflow: hidden;
  display: grid;
  place-items: center;
}
.stickypar__bg {
  position: absolute;
  inset: -20% 0;
  background: repeating-linear-gradient(45deg, rgba($color, .22) 0 18px, transparent 18px 36px);

  // ── 실제 사용 코드: 앞 문장은 sticky 로 붙박이, 뒤 배경만 흘러간다 ──
  @supports (animation-timeline: scroll()) {
    animation: bg-drift linear both;
    animation-timeline: scroll(root);
  }
  @supports not (animation-timeline: scroll()) { transform: none; }
}
.stickypar__caption {
  position: sticky;
  top: 40%;
  z-index: 1;
  margin: 0;
  padding: 12px 22px;
  border-radius: $r-pill;
  background: $stage-ink;
  color: $color;
  font: 700 clamp(14px, 4.4vw, 17px)/1 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

@keyframes bg-drift { from { transform: translateY(0); } to { transform: translateY(-#{$bg-shift}); } }

// ── 데모(.is-demo): 왕복 루프로 흉내 ────────
.stage.is-demo .stickypar__bg { animation: bg-loop $duration ease-in-out infinite; }
@keyframes bg-loop { 0%, 100% { transform: translateY($bg-shift); } 50% { transform: translateY(-$bg-shift); } }

@media (prefers-reduced-motion: reduce) {
  .stickypar__bg, .stage.is-demo .stickypar__bg { animation: none !important; transform: none; }
}

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);
}

.stickypar {
  position: relative;
  width: 100%;
  height: 100%;
  overflow: hidden;
  display: grid;
  place-items: center;
}

.stickypar__bg {
  position: absolute;
  inset: -20% 0;
  background: repeating-linear-gradient(45deg, rgba(255, 247, 230, 0.22) 0 18px, transparent 18px 36px);
}
@supports (animation-timeline: scroll()) {
  .stickypar__bg {
    animation: bg-drift linear both;
    animation-timeline: scroll(root);
  }
}
@supports not (animation-timeline: scroll()) {
  .stickypar__bg {
    transform: none;
  }
}

.stickypar__caption {
  position: sticky;
  top: 40%;
  z-index: 1;
  margin: 0;
  padding: 12px 22px;
  border-radius: 999px;
  background: #17141a;
  color: #fff7e6;
  font: 700 clamp(14px, 4.4vw, 17px)/1 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

@keyframes bg-drift {
  from {
    transform: translateY(0);
  }
  to {
    transform: translateY(-40px);
  }
}
.stage.is-demo .stickypar__bg {
  animation: bg-loop 2s ease-in-out infinite;
}

@keyframes bg-loop {
  0%, 100% {
    transform: translateY(40px);
  }
  50% {
    transform: translateY(-40px);
  }
}
@media (prefers-reduced-motion: reduce) {
  .stickypar__bg, .stage.is-demo .stickypar__bg {
    animation: none !important;
    transform: none;
  }
}

import type { CSSProperties, ReactNode } from "react";
import styles from "./StickyParallax.module.scss";

export type StickyParallaxProps = {
  children: ReactNode;
  /** 뒤 배경 이동량 (기본 40px) */
  bgShift?: number;
  /** 배경 결·문장 글자 색 */
  color?: string;
  className?: string;
};

type Vars = CSSProperties & { "--bg-shift"?: string; "--color"?: string };

export default function StickyParallax({
  children,
  bgShift = 40,
  color = "#fff7e6",
  className = "",
}: StickyParallaxProps) {
  const vars: Vars = { "--bg-shift": `${bgShift}px`, "--color": color };

  return (
    <div className={`${styles.wrap} ${className}`} style={vars}>
      <div className={styles.bg} aria-hidden="true" />
      <p className={styles.caption}>{children}</p>
    </div>
  );
}