06Shrinking header

<main class="stage">
  <header class="head is-demo">
    <span class="head__logo">GODRICH</span>
    <nav class="head__nav" aria-hidden="true">
      <span></span><span></span><span></span>
    </nav>
  </header>
  <div class="page">
    <p class="page__line"></p>
    <p class="page__line"></p>
    <p class="page__line short"></p>
  </div>
</main>

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

// ── 변수 3개. 변형은 이것만 바꾼다 (값은 토큰에서 받는다) ──────
$tall: 64px;                                     // 처음 헤더 높이
$short-scale: .75;                               // 줄어든 비율 (64px → 48px ≈ .75)
$color: $subject-ink;                            // 헤더 배경 (yellow 무대라 ink)

// ── 데모 무대 (zip 에서 지워도 된다) ──────────────────────────
html, body { margin: 0; overflow: hidden; }
.stage {
  min-height: 100vh;
  margin: 0;
  background: $stage-yellow;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

// ── 헤더: 높이 대신 transform: scaleY 로 "줄어든다" ────────────
// (height 는 애니메이션하면 레이아웃을 다시 계산한다 — 함정 섹션 참고)
.head {
  position: sticky;
  top: 0;
  height: $tall;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 clamp(16px, 5vw, 24px);
  background: $color;
  transform-origin: top; // 규칙8: 헤더가 top에서 얇아짐

  &__logo { color: #fff; font-weight: 800; font-size: 18px; line-height: 1; font-family: inherit; letter-spacing: .04em; }
  &__nav { display: flex; gap: 10px; span { width: 26px; height: 8px; border-radius: 4px; background: rgba(255, 255, 255, .35); } }

  // ── 실제 사용 코드: 문서 스크롤이 진행되는 동안 얇아진다 ──
  @supports (animation-timeline: scroll()) {
    animation: shrink-header linear both;
    animation-timeline: scroll(root);
    animation-range: 0 200px;
  }

  @supports not (animation-timeline: scroll()) {
    transform: none;
  }
}

@keyframes shrink-header {
  from { transform: scaleY(1); }
  to   { transform: scaleY($short-scale); }
}

// ── 데모(.is-demo): 스크롤 대신 2초 루프(줄었다 늘었다)로 흉내 ──
.head.is-demo {
  animation: shrink-loop $dur-loop ease-in-out infinite;
}
@keyframes shrink-loop {
  0%   { transform: scaleY(1); }
  50%  { transform: scaleY($short-scale); }
  100% { transform: scaleY(1); }
}

// ── 배경: 문서처럼 보이는 자리 ─────────────────────────
.page { padding: 28px 24px 0; }
.page__line {
  height: 12px;
  margin: 0 0 14px;
  border-radius: 4px;
  background: rgba(23, 20, 26, .14);
  &.short { width: 60%; }
}

// ── 접근성: 움직임 줄이기 설정이면 즉시 줄인 상태로 고정 ────────
@media (prefers-reduced-motion: reduce) {
  .head, .head.is-demo { animation: none !important; transform: scaleY($short-scale); }
}

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

.stage {
  min-height: 100vh;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
}

.head {
  position: sticky;
  top: 0;
  height: 64px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 clamp(16px, 5vw, 24px);
  background: #17141a;
  transform-origin: top;
}
.head__logo {
  color: #fff;
  font-weight: 800;
  font-size: 18px;
  line-height: 1;
  font-family: inherit;
  letter-spacing: 0.04em;
}
.head__nav {
  display: flex;
  gap: 10px;
}
.head__nav span {
  width: 26px;
  height: 8px;
  border-radius: 4px;
  background: rgba(255, 255, 255, 0.35);
}
@supports (animation-timeline: scroll()) {
  .head {
    animation: shrink-header linear both;
    animation-timeline: scroll(root);
    animation-range: 0 200px;
  }
}
@supports not (animation-timeline: scroll()) {
  .head {
    transform: none;
  }
}

@keyframes shrink-header {
  from {
    transform: scaleY(1);
  }
  to {
    transform: scaleY(0.75);
  }
}
.head.is-demo {
  animation: shrink-loop 2s ease-in-out infinite;
}

@keyframes shrink-loop {
  0% {
    transform: scaleY(1);
  }
  50% {
    transform: scaleY(0.75);
  }
  100% {
    transform: scaleY(1);
  }
}
.page {
  padding: 28px 24px 0;
}

.page__line {
  height: 12px;
  margin: 0 0 14px;
  border-radius: 4px;
  background: rgba(23, 20, 26, 0.14);
}
.page__line.short {
  width: 60%;
}

@media (prefers-reduced-motion: reduce) {
  .head, .head.is-demo {
    animation: none !important;
    transform: scaleY(0.75);
  }
}

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

export type ShrinkingHeaderProps = {
  logo: string;
  children?: ReactNode;
  /** 처음 헤더 높이 (기본 64px) */
  tall?: number;
  /** 줄어든 비율 (기본 .75 → 64px 기준 48px) */
  shortScale?: number;
  /** 헤더 배경 (기본 어두운색) */
  color?: string;
  className?: string;
};

type Vars = CSSProperties & { "--tall"?: string; "--short-scale"?: number; "--color"?: string };

export default function ShrinkingHeader({
  logo,
  children,
  tall = 64,
  shortScale = 0.75,
  color = "#17141a",
  className = "",
}: ShrinkingHeaderProps) {
  const vars: Vars = { "--tall": `${tall}px`, "--short-scale": shortScale, "--color": color };

  return (
    <header className={`${styles.head} ${className}`} style={vars}>
      <span className={styles.logo}>{logo}</span>
      <nav className={styles.nav}>{children}</nav>
    </header>
  );
}