02Phối cảnh 3 lớp

<main class="stage is-demo">
  <div class="layer3">
    <div class="layer3__back" aria-hidden="true"></div>
    <div class="layer3__mid" aria-hidden="true"></div>
    <div class="layer3__front" aria-hidden="true"></div>
    <h2 class="layer3__title">Phối cảnh 3 lớp</h2>
  </div>
</main>

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

// ── 변수 3개. 변형은 이것만 바꾼다 ──────────────────────────
$back-shift: 10px;                               // 뒤 레이어 이동량 (가장 적게)
$mid-shift: 26px;                                // 중간 레이어 이동량
$front-shift: 46px;                              // 앞 레이어 이동량 (가장 많이)

@include stage($stage-yellow);

.layer3 {
  position: relative;
  width: 100%;
  height: 100%;
  overflow: hidden;

  &__back, &__mid, &__front {
    position: absolute;
    border-radius: 50%;
    background: $subject-ink;
  }
  &__back {
    width: 70px; height: 70px; left: 14%; top: 20%; opacity: .18;
    @supports (animation-timeline: scroll()) { animation: drift-back linear both; animation-timeline: scroll(root); }
  }
  &__mid {
    width: 56px; height: 56px; left: 58%; top: 46%; opacity: .38;
    @supports (animation-timeline: scroll()) { animation: drift-mid linear both; animation-timeline: scroll(root); }
  }
  &__front {
    width: 40px; height: 40px; left: 30%; top: 66%; opacity: .82;
    @supports (animation-timeline: scroll()) { animation: drift-front linear both; animation-timeline: scroll(root); }
  }

  &__title {
    position: absolute;
    z-index: 1;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    margin: 0;
    padding: 14px 22px;
    border-radius: $r-pill;
    background: $stage-ink;
    color: #fff;
    font: 700 clamp(14px, 4.6vw, 18px)/1 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
    white-space: nowrap;
  }
}

// ── 실제 사용 코드: 세 레이어가 각각 다른 속도로 스크롤과 함께 이동한다 ──
@keyframes drift-back  { from { transform: translateY(0); } to { transform: translateY(-#{$back-shift}); } }
@keyframes drift-mid   { from { transform: translateY(0); } to { transform: translateY(-#{$mid-shift}); } }
@keyframes drift-front { from { transform: translateY(0); } to { transform: translateY(-#{$front-shift}); } }

// ── 데모(.is-demo): 왕복 루프로 흉내 ────────
.stage.is-demo .layer3__back  { animation: loop-back $dur-loop ease-in-out infinite; }
.stage.is-demo .layer3__mid   { animation: loop-mid $dur-loop ease-in-out infinite; }
.stage.is-demo .layer3__front { animation: loop-front $dur-loop ease-in-out infinite; }
@keyframes loop-back  { 0%, 100% { transform: translateY($back-shift); }  50% { transform: translateY(-$back-shift); } }
@keyframes loop-mid   { 0%, 100% { transform: translateY($mid-shift); }   50% { transform: translateY(-$mid-shift); } }
@keyframes loop-front { 0%, 100% { transform: translateY($front-shift); } 50% { transform: translateY(-$front-shift); } }

@media (prefers-reduced-motion: reduce) {
  .layer3__back, .layer3__mid, .layer3__front,
  .stage.is-demo .layer3__back, .stage.is-demo .layer3__mid, .stage.is-demo .layer3__front {
    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: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.layer3 {
  position: relative;
  width: 100%;
  height: 100%;
  overflow: hidden;
}
.layer3__back, .layer3__mid, .layer3__front {
  position: absolute;
  border-radius: 50%;
  background: #17141a;
}
.layer3__back {
  width: 70px;
  height: 70px;
  left: 14%;
  top: 20%;
  opacity: 0.18;
}
@supports (animation-timeline: scroll()) {
  .layer3__back {
    animation: drift-back linear both;
    animation-timeline: scroll(root);
  }
}
.layer3__mid {
  width: 56px;
  height: 56px;
  left: 58%;
  top: 46%;
  opacity: 0.38;
}
@supports (animation-timeline: scroll()) {
  .layer3__mid {
    animation: drift-mid linear both;
    animation-timeline: scroll(root);
  }
}
.layer3__front {
  width: 40px;
  height: 40px;
  left: 30%;
  top: 66%;
  opacity: 0.82;
}
@supports (animation-timeline: scroll()) {
  .layer3__front {
    animation: drift-front linear both;
    animation-timeline: scroll(root);
  }
}
.layer3__title {
  position: absolute;
  z-index: 1;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  margin: 0;
  padding: 14px 22px;
  border-radius: 999px;
  background: #17141a;
  color: #fff;
  font: 700 clamp(14px, 4.6vw, 18px)/1 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  white-space: nowrap;
}

@keyframes drift-back {
  from {
    transform: translateY(0);
  }
  to {
    transform: translateY(-10px);
  }
}
@keyframes drift-mid {
  from {
    transform: translateY(0);
  }
  to {
    transform: translateY(-26px);
  }
}
@keyframes drift-front {
  from {
    transform: translateY(0);
  }
  to {
    transform: translateY(-46px);
  }
}
.stage.is-demo .layer3__back {
  animation: loop-back 2s ease-in-out infinite;
}

.stage.is-demo .layer3__mid {
  animation: loop-mid 2s ease-in-out infinite;
}

.stage.is-demo .layer3__front {
  animation: loop-front 2s ease-in-out infinite;
}

@keyframes loop-back {
  0%, 100% {
    transform: translateY(10px);
  }
  50% {
    transform: translateY(-10px);
  }
}
@keyframes loop-mid {
  0%, 100% {
    transform: translateY(26px);
  }
  50% {
    transform: translateY(-26px);
  }
}
@keyframes loop-front {
  0%, 100% {
    transform: translateY(46px);
  }
  50% {
    transform: translateY(-46px);
  }
}
@media (prefers-reduced-motion: reduce) {
  .layer3__back, .layer3__mid, .layer3__front,
  .stage.is-demo .layer3__back, .stage.is-demo .layer3__mid, .stage.is-demo .layer3__front {
    animation: none !important;
    transform: none;
  }
}

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

export type ThreeLayerDepthProps = {
  children: ReactNode;
  /** 뒤 레이어 이동량 (기본 10px) */
  backShift?: number;
  /** 중간 레이어 이동량 (기본 26px) */
  midShift?: number;
  /** 앞 레이어 이동량 (기본 46px) */
  frontShift?: number;
  className?: string;
};

type Vars = CSSProperties & {
  "--back-shift"?: string;
  "--mid-shift"?: string;
  "--front-shift"?: string;
};

export default function ThreeLayerDepth({
  children,
  backShift = 10,
  midShift = 26,
  frontShift = 46,
  className = "",
}: ThreeLayerDepthProps) {
  const vars: Vars = {
    "--back-shift": `${backShift}px`,
    "--mid-shift": `${midShift}px`,
    "--front-shift": `${frontShift}px`,
  };

  return (
    <div className={`${styles.layer3} ${className}`} style={vars}>
      <div className={styles.back} aria-hidden="true" />
      <div className={styles.mid} aria-hidden="true" />
      <div className={styles.front} aria-hidden="true" />
      <div className={styles.title}>{children}</div>
    </div>
  );
}