9 CSS Scroll Progress Bar — không cần JS

<main class="stage">
  <div class="track" role="progressbar" aria-label="Tiến độ đọc" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0">
    <div class="bar is-demo"></div>
  </div>
  <div class="page">
    <div class="page__block"></div>
    <div class="page__block"></div>
    <div class="page__block short"></div>
  </div>
</main>

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

// ── 변수 3개. 변형은 이것만 바꾼다 ──────────────────────────
$thickness: 3px;                                   // 바 두께. 굵게 6px
$color: $subject-blue;                              // 채워진 구간 색
$track: rgba(255, 255, 255, .16);                    // 안 읽은 구간

@include stage($stage-ink);

.track {
  position: fixed;
  top: 0; left: 0; right: 0;
  height: $thickness;
  background: $track;
}

.bar {
  height: 100%;
  width: 100%;
  background: $color;
  transform: scaleX(0);
  transform-origin: left; // 규칙8: 진행바 left 채움

  // 실제 사용: 문서 스크롤 진행률이 곧 바 길이 (Chrome·Edge 115+ · Safari 26+ · Firefox 158+ 플래그, 편브리프 표)
  @supports (animation-timeline: scroll()) {
    animation: fill linear both;
    animation-timeline: scroll(root);
  }
}
@keyframes fill { to { transform: scaleX(1); } }

// ── 데모(.is-demo): 스크롤 없이 2초 루프로 흉내 ────────────────
.bar.is-demo { animation: fill-loop $dur-loop linear infinite; }
@keyframes fill-loop {
  0%   { transform: scaleX(0); }
  92%  { transform: scaleX(1); }
  100% { transform: scaleX(1); }
}

.page { padding: $sp-10 $sp-6 0; }
.page__block {
  height: $sp-6;
  margin: 0 0 $sp-4;
  border-radius: $r-sm;
  background: rgba(255, 255, 255, .12);
  &.short { width: 55%; }
}

// ── 접근성: 움직임 줄이기 — 다 채워진 상태로 고정 ────────────
@media (prefers-reduced-motion: reduce) {
  .bar, .bar.is-demo { animation: none !important; transform: scaleX(1); }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.track {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: rgba(255, 255, 255, 0.16);
}

.bar {
  height: 100%;
  width: 100%;
  background: #2f6df6;
  transform: scaleX(0);
  transform-origin: left;
}
@supports (animation-timeline: scroll()) {
  .bar {
    animation: fill linear both;
    animation-timeline: scroll(root);
  }
}

@keyframes fill {
  to {
    transform: scaleX(1);
  }
}
.bar.is-demo {
  animation: fill-loop 2s linear infinite;
}

@keyframes fill-loop {
  0% {
    transform: scaleX(0);
  }
  92% {
    transform: scaleX(1);
  }
  100% {
    transform: scaleX(1);
  }
}
.page {
  padding: 40px 24px 0;
}

.page__block {
  height: 24px;
  margin: 0 0 16px;
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.12);
}
.page__block.short {
  width: 55%;
}

@media (prefers-reduced-motion: reduce) {
  .bar, .bar.is-demo {
    animation: none !important;
    transform: scaleX(1);
  }
}

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

export type TopBarProps = {
  /** 바 두께 (기본 3px) */
  thickness?: number;
  /** 바 색 */
  color?: string;
};

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

// 실제 쓰임: 문서 스크롤 비율을 window scroll 로 재서 --scale 에 반영한다.
// scroll() 타임라인을 쓸 수 있는 브라우저(Chrome·Edge 115+, Safari 26+)에서는 CSS 만으로도 되지만,
// React 컴포넌트는 아직 지원이 갈린 Firefox 를 포함해 항상 움직여야 하므로 스크롤 리스너로 재계산한다.
export default function TopBar({ thickness = 3, color = "#2f6df6" }: TopBarProps) {
  const [scale, setScale] = useState(0);

  useEffect(() => {
    const onScroll = () => {
      const max = document.documentElement.scrollHeight - window.innerHeight;
      setScale(max > 0 ? Math.min(1, window.scrollY / max) : 0);
    };
    onScroll();
    window.addEventListener("scroll", onScroll, { passive: true });
    return () => window.removeEventListener("scroll", onScroll);
  }, []);

  const vars: Vars = { "--thickness": `${thickness}px`, "--color": color };

  return (
    <div className={styles.track} style={vars} role="progressbar" aria-label="Reading progress"
         aria-valuemin={0} aria-valuemax={100} aria-valuenow={Math.round(scale * 100)}>
      <div className={styles.bar} style={{ transform: `scaleX(${scale})` }} />
    </div>
  );
}

<main class="stage">
  <div class="badge is-demo" role="progressbar" aria-label="Lên đầu trang" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0">
    <span class="badge__inner"><span class="badge__arrow" aria-hidden="true"></span></span>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$size: 56px;                                        // 배지 지름
$color: $subject-ink;                               // 링 색
$duration: $dur-loop;                               // 한 바퀴(스크롤 전체) 도는 시간

@include stage($stage-yellow);

// 정수라야 링 각도가 매끄럽게 보간된다
@property --p {
  syntax: '<number>';
  initial-value: 0;
  inherits: false;
}

.badge {
  --p: 0;
  position: fixed;
  right: $sp-6; bottom: $sp-6;
  width: $size; height: $size;
  border-radius: 50%;
  display: grid;
  place-items: center;
  background: conic-gradient($color calc(var(--p) * 1%), $stage-paper 0);
  box-shadow: $shadow-raised;

  // 실제 사용: 링 배지는 플로팅 위로가기 버튼에 흔히 결합된다
  @supports (animation-timeline: scroll()) {
    animation: fill-ring linear both;
    animation-timeline: scroll(root);
  }
}
@keyframes fill-ring { from { --p: 0; } to { --p: 100; } }

.badge.is-demo { animation: fill-ring-loop $duration linear infinite; }
@keyframes fill-ring-loop {
  0%   { --p: 0; }
  92%  { --p: 100; }
  100% { --p: 100; }
}

.badge__inner {
  width: 44px; height: 44px;
  border-radius: 50%;
  background: $stage-paper;
  display: grid;
  place-items: center;
}
.badge__arrow {
  width: 0; height: 0;
  border-left: 6px solid transparent;
  border-right: 6px solid transparent;
  border-bottom: 9px solid $subject-ink;
}

@media (prefers-reduced-motion: reduce) {
  .badge, .badge.is-demo { animation: none !important; --p: 100; }
}

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);
}

@property --p {
  syntax: "<number>";
  initial-value: 0;
  inherits: false;
}
.badge {
  --p: 0;
  position: fixed;
  right: 24px;
  bottom: 24px;
  width: 56px;
  height: 56px;
  border-radius: 50%;
  display: grid;
  place-items: center;
  background: conic-gradient(#17141a calc(var(--p) * 1%), #ffffff 0);
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
}
@supports (animation-timeline: scroll()) {
  .badge {
    animation: fill-ring linear both;
    animation-timeline: scroll(root);
  }
}

@keyframes fill-ring {
  from {
    --p: 0;
  }
  to {
    --p: 100;
  }
}
.badge.is-demo {
  animation: fill-ring-loop 2s linear infinite;
}

@keyframes fill-ring-loop {
  0% {
    --p: 0;
  }
  92% {
    --p: 100;
  }
  100% {
    --p: 100;
  }
}
.badge__inner {
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: #ffffff;
  display: grid;
  place-items: center;
}

.badge__arrow {
  width: 0;
  height: 0;
  border-left: 6px solid transparent;
  border-right: 6px solid transparent;
  border-bottom: 9px solid #17141a;
}

@media (prefers-reduced-motion: reduce) {
  .badge, .badge.is-demo {
    animation: none !important;
    --p: 100;
  }
}

import { useEffect, useState } from "react";
import type { CSSProperties, MouseEvent } from "react";
import styles from "./RingBadge.module.scss";

export type RingBadgeProps = {
  /** 배지 지름 (기본 56px) */
  size?: number;
  /** 링 색 */
  color?: string;
  onClick?: (e: MouseEvent<HTMLButtonElement>) => void;
};

type Vars = CSSProperties & { "--size"?: string; "--color"?: string; "--p"?: number };

// 실제 쓰임: 위로가기 버튼과 결합. percent 만큼 conic-gradient 링이 채워진다.
export default function RingBadge({ size = 56, color = "#17141a", onClick }: RingBadgeProps) {
  const [percent, setPercent] = useState(0);

  useEffect(() => {
    const onScroll = () => {
      const max = document.documentElement.scrollHeight - window.innerHeight;
      setPercent(max > 0 ? Math.min(100, Math.round((window.scrollY / max) * 100)) : 0);
    };
    onScroll();
    window.addEventListener("scroll", onScroll, { passive: true });
    return () => window.removeEventListener("scroll", onScroll);
  }, []);

  const vars: Vars = { "--size": `${size}px`, "--color": color, "--p": percent };

  return (
    <button
      type="button"
      className={styles.badge}
      style={vars}
      role="progressbar"
      aria-label="Back to top"
      aria-valuemin={0}
      aria-valuemax={100}
      aria-valuenow={percent}
      onClick={(e: MouseEvent<HTMLButtonElement>) => { window.scrollTo({ top: 0, behavior: "smooth" }); onClick?.(e); }}
    >
      <span className={styles.inner}><span className={styles.arrow} /></span>
    </button>
  );
}

<main class="stage">
  <nav class="dots is-demo" aria-label="Điều hướng section">
    <span class="dot" aria-hidden="true"></span>
    <span class="dot" aria-hidden="true"></span>
    <span class="dot" aria-hidden="true"></span>
    <span class="dot" aria-hidden="true"></span>
    <span class="dot" aria-hidden="true"></span>
    <span class="dot" aria-hidden="true"></span>
  </nav>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;                               // 점 하나가 켜졌다 꺼지는 한 순환
$easing: $ease-out;
$color: $subject-cream;                             // 활성 점 색

@include stage($stage-orange);

.dots {
  position: fixed;
  right: $sp-6; top: 50%;
  transform: translateY(-50%);
  display: flex;
  flex-direction: column;
  gap: $sp-3;
}

.dot {
  width: 8px; height: 8px;
  border-radius: 50%;
  background: rgba(23, 20, 26, .28);
  transition: transform 200ms $easing, background 200ms $easing;
}

// ── 실제 사용: 섹션이 뷰포트에 들어오는 순간 그 섹션의 점에 .is-active 를 켠다 (IntersectionObserver) ──
.dot.is-active { transform: scale(1.6); background: $color; }

// ── 데모: 점을 순서대로 하나씩 밝힌다 ────────────────────
.dots.is-demo .dot { animation: pulse $duration linear infinite; }
.dots.is-demo .dot:nth-child(1) { animation-delay: 0s; }
.dots.is-demo .dot:nth-child(2) { animation-delay: .333s; }
.dots.is-demo .dot:nth-child(3) { animation-delay: .667s; }
.dots.is-demo .dot:nth-child(4) { animation-delay: 1s; }
.dots.is-demo .dot:nth-child(5) { animation-delay: 1.333s; }
.dots.is-demo .dot:nth-child(6) { animation-delay: 1.667s; }

@keyframes pulse {
  0%, 83.34%, 100% { transform: scale(1);   background: rgba(23, 20, 26, .28); }
  8.33%, 16.66%     { transform: scale(1.6); background: $color; }
}

@media (prefers-reduced-motion: reduce) {
  .dots.is-demo .dot { animation: none !important; }
  .dots.is-demo .dot:first-child { transform: scale(1.6); background: $color; }
}

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);
}

.dots {
  position: fixed;
  right: 24px;
  top: 50%;
  transform: translateY(-50%);
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: rgba(23, 20, 26, 0.28);
  transition: transform 200ms ease-out, background 200ms ease-out;
}

.dot.is-active {
  transform: scale(1.6);
  background: #fff7e6;
}

.dots.is-demo .dot {
  animation: pulse 2s linear infinite;
}

.dots.is-demo .dot:nth-child(1) {
  animation-delay: 0s;
}

.dots.is-demo .dot:nth-child(2) {
  animation-delay: 0.333s;
}

.dots.is-demo .dot:nth-child(3) {
  animation-delay: 0.667s;
}

.dots.is-demo .dot:nth-child(4) {
  animation-delay: 1s;
}

.dots.is-demo .dot:nth-child(5) {
  animation-delay: 1.333s;
}

.dots.is-demo .dot:nth-child(6) {
  animation-delay: 1.667s;
}

@keyframes pulse {
  0%, 83.34%, 100% {
    transform: scale(1);
    background: rgba(23, 20, 26, 0.28);
  }
  8.33%, 16.66% {
    transform: scale(1.6);
    background: #fff7e6;
  }
}
@media (prefers-reduced-motion: reduce) {
  .dots.is-demo .dot {
    animation: none !important;
  }
  .dots.is-demo .dot:first-child {
    transform: scale(1.6);
    background: #fff7e6;
  }
}

import { useEffect, useState } from "react";
import styles from "./SectionDots.module.scss";

export type SectionDotsProps = {
  /** 관찰할 섹션 id 목록 (순서대로) */
  sectionIds: string[];
  /** 활성 점 색 */
  color?: string;
};

// 실제 쓰임: IntersectionObserver 로 지금 뷰포트에 가장 많이 걸친 섹션을 찾아 그 점만 켠다.
export default function SectionDots({ sectionIds, color = "#fff7e6" }: SectionDotsProps) {
  const [active, setActive] = useState(0);

  useEffect(() => {
    const els = sectionIds.map((id) => document.getElementById(id)).filter(Boolean) as HTMLElement[];
    const io = new IntersectionObserver(
      (entries) => {
        const top = entries.filter((e) => e.isIntersecting).sort((a, b) => b.intersectionRatio - a.intersectionRatio)[0];
        if (top) setActive(els.indexOf(top.target as HTMLElement));
      },
      { threshold: [0.3, 0.6] }
    );
    els.forEach((el) => io.observe(el));
    return () => io.disconnect();
  }, [sectionIds]);

  return (
    <nav className={styles.dots} aria-label="Section navigation">
      {sectionIds.map((id, i) => (
        <a
          key={id}
          href={`#${id}`}
          className={`${styles.dot} ${i === active ? styles.active : ""}`}
          style={i === active ? { background: color } : undefined}
          aria-hidden="true"
          tabIndex={-1}
        />
      ))}
    </nav>
  );
}

<main class="stage">
  <div class="rail" role="progressbar" aria-label="Vị trí đã đọc" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0">
    <div class="rail__fill is-demo"></div>
  </div>
  <div class="page">
    <div class="page__block"></div>
    <div class="page__block"></div>
    <div class="page__block short"></div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$thickness: 4px;                                    // 레일 두께
$color: $subject-blue;                              // 채워진 구간 색
$track: rgba(23, 20, 26, .1);                       // 안 읽은 구간

@include stage($stage-paper);

.rail {
  position: fixed;
  top: 0; right: 0;
  width: $thickness;
  height: 100%;
  background: $track;
}

.rail__fill {
  width: 100%;
  height: 100%;
  background: $color;
  transform: scaleY(0);
  transform-origin: top; // 규칙8: 세로레일 top 채움

  // 실제 사용: 문서 안에서 지금까지 읽은 위치를 세로로 보여준다
  @supports (animation-timeline: scroll()) {
    animation: fill-y linear both;
    animation-timeline: scroll(root);
  }
}
@keyframes fill-y { to { transform: scaleY(1); } }

.rail__fill.is-demo { animation: fill-y-loop $dur-loop linear infinite; }
@keyframes fill-y-loop {
  0%   { transform: scaleY(0); }
  92%  { transform: scaleY(1); }
  100% { transform: scaleY(1); }
}

.page { padding: $sp-10 $sp-8 0 $sp-6; }
.page__block {
  height: $sp-6;
  margin: 0 0 $sp-4;
  border-radius: $r-sm;
  background: rgba(23, 20, 26, .08);
  &.short { width: 55%; }
}

@media (prefers-reduced-motion: reduce) {
  .rail__fill, .rail__fill.is-demo { animation: none !important; transform: scaleY(1); }
}

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);
}

.rail {
  position: fixed;
  top: 0;
  right: 0;
  width: 4px;
  height: 100%;
  background: rgba(23, 20, 26, 0.1);
}

.rail__fill {
  width: 100%;
  height: 100%;
  background: #2f6df6;
  transform: scaleY(0);
  transform-origin: top;
}
@supports (animation-timeline: scroll()) {
  .rail__fill {
    animation: fill-y linear both;
    animation-timeline: scroll(root);
  }
}

@keyframes fill-y {
  to {
    transform: scaleY(1);
  }
}
.rail__fill.is-demo {
  animation: fill-y-loop 2s linear infinite;
}

@keyframes fill-y-loop {
  0% {
    transform: scaleY(0);
  }
  92% {
    transform: scaleY(1);
  }
  100% {
    transform: scaleY(1);
  }
}
.page {
  padding: 40px 32px 0 24px;
}

.page__block {
  height: 24px;
  margin: 0 0 16px;
  border-radius: 8px;
  background: rgba(23, 20, 26, 0.08);
}
.page__block.short {
  width: 55%;
}

@media (prefers-reduced-motion: reduce) {
  .rail__fill, .rail__fill.is-demo {
    animation: none !important;
    transform: scaleY(1);
  }
}

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

export type SideRailProps = {
  /** 레일 두께 (기본 4px) */
  thickness?: number;
  /** 채워진 구간 색 */
  color?: string;
};

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

// 실제 쓰임: TopBar 와 같은 계산을 세로(scaleY)로 그린다.
export default function SideRail({ thickness = 4, color = "#2f6df6" }: SideRailProps) {
  const [scale, setScale] = useState(0);

  useEffect(() => {
    const onScroll = () => {
      const max = document.documentElement.scrollHeight - window.innerHeight;
      setScale(max > 0 ? Math.min(1, window.scrollY / max) : 0);
    };
    onScroll();
    window.addEventListener("scroll", onScroll, { passive: true });
    return () => window.removeEventListener("scroll", onScroll);
  }, []);

  const vars: Vars = { "--thickness": `${thickness}px`, "--color": color };

  return (
    <div className={styles.rail} style={vars} role="progressbar" aria-label="Reading position"
         aria-valuemin={0} aria-valuemax={100} aria-valuenow={Math.round(scale * 100)}>
      <div className={styles.fill} style={{ transform: `scaleY(${scale})` }} />
    </div>
  );
}

<main class="stage">
  <h2 class="headline is-demo">Tiêu đề được tô đầy theo mức đã đọc</h2>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$color: $subject-blue;                              // 읽은 구간 색
$dim: rgba(255, 255, 255, .32);                     // 안 읽은 구간 색
$duration: $dur-loop;

@include stage($stage-ink);

// 퍼센트라야 그라데이션 경계가 매끄럽게 보간된다
@property --p {
  syntax: '<percentage>';
  initial-value: 0%;
  inherits: false;
}

.headline {
  --p: 0%;
  max-width: 80%;
  margin: 0;
  text-align: center;
  font-weight: 800;
  font-size: clamp(20px, 6vw, 28px);
  line-height: 1.35;
  font-family: inherit;
  background-image: linear-gradient(90deg, $color var(--p), $dim var(--p));
  background-clip: text;
  -webkit-background-clip: text;
  color: transparent;

  // 실제 사용: 헤드라인 색이 스크롤 진행률만큼 왼쪽부터 채워진다
  @supports (animation-timeline: scroll()) {
    animation: fill-text linear both;
    animation-timeline: scroll(root);
  }
}
@keyframes fill-text { from { --p: 0%; } to { --p: 100%; } }

.headline.is-demo { animation: fill-text-loop $duration linear infinite; }
@keyframes fill-text-loop {
  0%   { --p: 0%; }
  92%  { --p: 100%; }
  100% { --p: 100%; }
}

@media (prefers-reduced-motion: reduce) {
  .headline, .headline.is-demo { animation: none !important; --p: 100%; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

@property --p {
  syntax: "<percentage>";
  initial-value: 0%;
  inherits: false;
}
.headline {
  --p: 0%;
  max-width: 80%;
  margin: 0;
  text-align: center;
  font-weight: 800;
  font-size: clamp(20px, 6vw, 28px);
  line-height: 1.35;
  font-family: inherit;
  background-image: linear-gradient(90deg, #2f6df6 var(--p), rgba(255, 255, 255, 0.32) var(--p));
  background-clip: text;
  -webkit-background-clip: text;
  color: transparent;
}
@supports (animation-timeline: scroll()) {
  .headline {
    animation: fill-text linear both;
    animation-timeline: scroll(root);
  }
}

@keyframes fill-text {
  from {
    --p: 0%;
  }
  to {
    --p: 100%;
  }
}
.headline.is-demo {
  animation: fill-text-loop 2s linear infinite;
}

@keyframes fill-text-loop {
  0% {
    --p: 0%;
  }
  92% {
    --p: 100%;
  }
  100% {
    --p: 100%;
  }
}
@media (prefers-reduced-motion: reduce) {
  .headline, .headline.is-demo {
    animation: none !important;
    --p: 100%;
  }
}

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

export type TextFillProps = {
  children: ReactNode;
  /** 읽은 구간 색 */
  color?: string;
  /** 안 읽은 구간 색 */
  dim?: string;
};

type Vars = CSSProperties & { "--p"?: string; "--color"?: string; "--dim"?: string };

// 실제 쓰임: 헤드라인 색이 스크롤 진행률만큼 왼쪽부터 채워진다.
export default function TextFill({ children, color = "#2f6df6", dim = "rgba(255,255,255,.32)" }: TextFillProps) {
  const [percent, setPercent] = useState(0);

  useEffect(() => {
    const onScroll = () => {
      const max = document.documentElement.scrollHeight - window.innerHeight;
      setPercent(max > 0 ? Math.min(100, (window.scrollY / max) * 100) : 0);
    };
    onScroll();
    window.addEventListener("scroll", onScroll, { passive: true });
    return () => window.removeEventListener("scroll", onScroll);
  }, []);

  const vars: Vars = { "--p": `${percent}%`, "--color": color, "--dim": dim };

  return <h2 className={styles.headline} style={vars}>{children}</h2>;
}

<main class="stage">
  <div class="counter" role="status" aria-label="Tiến độ đọc">
    <span class="counter__num is-demo" aria-hidden="true"></span>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$color: $subject-ink;                               // 숫자 색
$duration: $dur-loop;
$easing: linear;                                    // 스크롤과 1:1로 움직이니 linear 가 맞다

@include stage($stage-yellow);

// 정수라야 애니메이션 중간값도 정수로 보간된다 (029 와 같은 기법)
@property --num {
  syntax: '<integer>';
  initial-value: 0;
  inherits: false;
}

.counter {
  position: fixed;
  top: $sp-6; right: $sp-6;
}

.counter__num {
  --num: 0;
  counter-reset: num var(--num);
  display: block;
  font-weight: 800;
  font-size: clamp(26px, 8vw, 36px);
  line-height: 1;
  font-family: inherit;
  font-variant-numeric: tabular-nums;
  color: $color;

  &::before { content: counter(num) '%'; }

  // 실제 사용: 전체 문서를 스크롤한 비율이 그대로 숫자가 된다
  @supports (animation-timeline: scroll()) {
    animation: count-up $easing both;
    animation-timeline: scroll(root);
  }
}
@keyframes count-up { from { --num: 0; } to { --num: 100; } }

.counter__num.is-demo { animation: count-up-loop $duration $easing infinite; }
@keyframes count-up-loop {
  0%   { --num: 0; }
  92%  { --num: 100; }
  100% { --num: 100; }
}

@media (prefers-reduced-motion: reduce) {
  .counter__num, .counter__num.is-demo { animation: none !important; --num: 100; }
}

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);
}

@property --num {
  syntax: "<integer>";
  initial-value: 0;
  inherits: false;
}
.counter {
  position: fixed;
  top: 24px;
  right: 24px;
}

.counter__num {
  --num: 0;
  counter-reset: num var(--num);
  display: block;
  font-weight: 800;
  font-size: clamp(26px, 8vw, 36px);
  line-height: 1;
  font-family: inherit;
  font-variant-numeric: tabular-nums;
  color: #17141a;
}
.counter__num::before {
  content: counter(num) "%";
}
@supports (animation-timeline: scroll()) {
  .counter__num {
    animation: count-up linear both;
    animation-timeline: scroll(root);
  }
}

@keyframes count-up {
  from {
    --num: 0;
  }
  to {
    --num: 100;
  }
}
.counter__num.is-demo {
  animation: count-up-loop 2s linear infinite;
}

@keyframes count-up-loop {
  0% {
    --num: 0;
  }
  92% {
    --num: 100;
  }
  100% {
    --num: 100;
  }
}
@media (prefers-reduced-motion: reduce) {
  .counter__num, .counter__num.is-demo {
    animation: none !important;
    --num: 100;
  }
}

import { useEffect, useState } from "react";
import styles from "./PercentCounter.module.scss";

export type PercentCounterProps = {
  /** 숫자 색 */
  color?: string;
};

// 실제 쓰임: 스크롤 진행률을 그대로 정수 퍼센트로 보여준다.
export default function PercentCounter({ color = "#17141a" }: PercentCounterProps) {
  const [percent, setPercent] = useState(0);

  useEffect(() => {
    const onScroll = () => {
      const max = document.documentElement.scrollHeight - window.innerHeight;
      setPercent(max > 0 ? Math.min(100, Math.round((window.scrollY / max) * 100)) : 0);
    };
    onScroll();
    window.addEventListener("scroll", onScroll, { passive: true });
    return () => window.removeEventListener("scroll", onScroll);
  }, []);

  return (
    <div className={styles.counter} role="status" aria-label="Reading progress">
      <span className={styles.num} style={{ color }}>{percent}%</span>
    </div>
  );
}

<main class="stage">
  <ol class="steps is-demo" aria-label="Tiến độ chương">
    <li class="step"><span class="step__circle">1</span></li>
    <li class="step"><span class="step__circle">2</span></li>
    <li class="step"><span class="step__circle">3</span></li>
    <li class="step"><span class="step__circle">4</span></li>
  </ol>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;
$color: $subject-cream;                             // 채워진 원 색
$track: rgba(255, 255, 255, .22);                    // 연결선 색

@include stage($stage-orange);

.steps {
  position: relative;
  display: flex;
  gap: $sp-6;
  margin: 0; padding: 0;
  list-style: none;
}

.step {
  position: relative;
  &:not(:first-child)::before {
    content: "";
    position: absolute;
    right: 100%; top: 50%;
    width: $sp-6; height: 2px;
    background: $track;
  }
}

.step__circle {
  display: grid;
  place-items: center;
  width: 28px; height: 28px;
  border-radius: 50%;
  border: 2px solid $track;
  background: transparent;
  color: $subject-ink;                 // AA: 채워지기 전 원 숫자 — 주황 무대 위 5.50:1
  font-weight: 700;
  font-size: 13px;
  line-height: 1;
  font-family: inherit;
}

// ── 실제 사용: 같은 스텝 키프레임을 시간 대신 스크롤 구간(animation-range)에 건다 ──
// .step:nth-child(2) .step__circle { animation: fill-2 linear both; animation-timeline: scroll(root); }

// ── 데모: 챕터 번호가 순서대로 하나씩 부풀며 채워지고, 루프가 돌면 처음으로 되돌아간다 ──
// (색만 순간 전환하면 프레임 사이 변화가 한두 장뿐이라 눈에 덜 띈다 — scale 팝으로 구간을 넓힌다)
.steps.is-demo .step:nth-child(1) .step__circle { animation: fill-1 $duration ease-out infinite; }
.steps.is-demo .step:nth-child(2) .step__circle { animation: fill-2 $duration ease-out infinite; }
.steps.is-demo .step:nth-child(3) .step__circle { animation: fill-3 $duration ease-out infinite; }
.steps.is-demo .step:nth-child(4) .step__circle { animation: fill-4 $duration ease-out infinite; }

@keyframes fill-1 {
  0%          { background: transparent; color: $subject-ink; border-color: $track; transform: scale(1); }
  8%          { background: $color; color: $subject-ink; border-color: $color; transform: scale(1.25); }
  15%, 100%   { background: $color; color: $subject-ink; border-color: $color; transform: scale(1); }
}
@keyframes fill-2 {
  0%, 25%     { background: transparent; color: $subject-ink; border-color: $track; transform: scale(1); }
  33%         { background: $color; color: $subject-ink; border-color: $color; transform: scale(1.25); }
  40%, 100%   { background: $color; color: $subject-ink; border-color: $color; transform: scale(1); }
}
@keyframes fill-3 {
  0%, 50%     { background: transparent; color: $subject-ink; border-color: $track; transform: scale(1); }
  58%         { background: $color; color: $subject-ink; border-color: $color; transform: scale(1.25); }
  65%, 100%   { background: $color; color: $subject-ink; border-color: $color; transform: scale(1); }
}
@keyframes fill-4 {
  0%, 75%     { background: transparent; color: $subject-ink; border-color: $track; transform: scale(1); }
  83%         { background: $color; color: $subject-ink; border-color: $color; transform: scale(1.25); }
  90%, 100%   { background: $color; color: $subject-ink; border-color: $color; transform: scale(1); }
}

@media (prefers-reduced-motion: reduce) {
  .steps.is-demo .step__circle { animation: none !important; background: $color; border-color: $color; }
}

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);
}

.steps {
  position: relative;
  display: flex;
  gap: 24px;
  margin: 0;
  padding: 0;
  list-style: none;
}

.step {
  position: relative;
}
.step:not(:first-child)::before {
  content: "";
  position: absolute;
  right: 100%;
  top: 50%;
  width: 24px;
  height: 2px;
  background: rgba(255, 255, 255, 0.22);
}

.step__circle {
  display: grid;
  place-items: center;
  width: 28px;
  height: 28px;
  border-radius: 50%;
  border: 2px solid rgba(255, 255, 255, 0.22);
  background: transparent;
  color: #17141a;
  font-weight: 700;
  font-size: 13px;
  line-height: 1;
  font-family: inherit;
}

.steps.is-demo .step:nth-child(1) .step__circle {
  animation: fill-1 2s ease-out infinite;
}

.steps.is-demo .step:nth-child(2) .step__circle {
  animation: fill-2 2s ease-out infinite;
}

.steps.is-demo .step:nth-child(3) .step__circle {
  animation: fill-3 2s ease-out infinite;
}

.steps.is-demo .step:nth-child(4) .step__circle {
  animation: fill-4 2s ease-out infinite;
}

@keyframes fill-1 {
  0% {
    background: transparent;
    color: #17141a;
    border-color: rgba(255, 255, 255, 0.22);
    transform: scale(1);
  }
  8% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1.25);
  }
  15%, 100% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1);
  }
}
@keyframes fill-2 {
  0%, 25% {
    background: transparent;
    color: #17141a;
    border-color: rgba(255, 255, 255, 0.22);
    transform: scale(1);
  }
  33% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1.25);
  }
  40%, 100% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1);
  }
}
@keyframes fill-3 {
  0%, 50% {
    background: transparent;
    color: #17141a;
    border-color: rgba(255, 255, 255, 0.22);
    transform: scale(1);
  }
  58% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1.25);
  }
  65%, 100% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1);
  }
}
@keyframes fill-4 {
  0%, 75% {
    background: transparent;
    color: #17141a;
    border-color: rgba(255, 255, 255, 0.22);
    transform: scale(1);
  }
  83% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1.25);
  }
  90%, 100% {
    background: #fff7e6;
    color: #17141a;
    border-color: #fff7e6;
    transform: scale(1);
  }
}
@media (prefers-reduced-motion: reduce) {
  .steps.is-demo .step__circle {
    animation: none !important;
    background: #fff7e6;
    border-color: #fff7e6;
  }
}

import { useEffect, useState } from "react";
import styles from "./ChapterSteps.module.scss";

export type ChapterStepsProps = {
  /** 챕터 수 */
  total: number;
  /** 채워진 원 색 */
  color?: string;
};

// 실제 쓰임: 전체 스크롤 진행률을 챕터 수로 나눠 지금 챕터를 계산한다.
export default function ChapterSteps({ total, color = "#fff7e6" }: ChapterStepsProps) {
  const [current, setCurrent] = useState(0);

  useEffect(() => {
    const onScroll = () => {
      const max = document.documentElement.scrollHeight - window.innerHeight;
      const p = max > 0 ? Math.min(1, window.scrollY / max) : 0;
      setCurrent(Math.min(total - 1, Math.floor(p * total)));
    };
    onScroll();
    window.addEventListener("scroll", onScroll, { passive: true });
    return () => window.removeEventListener("scroll", onScroll);
  }, [total]);

  return (
    <ol className={styles.steps} aria-label="Chapter progress">
      {Array.from({ length: total }, (_, i) => (
        <li key={i} className={styles.step}>
          <span className={styles.circle} style={i <= current ? { background: color, borderColor: color } : undefined}>
            {i + 1}
          </span>
        </li>
      ))}
    </ol>
  );
}

<main class="stage">
  <nav class="toc is-demo" aria-label="Mục lục">
    <span class="toc__pill" aria-hidden="true"></span>
    <a class="toc__item" href="#" tabindex="-1">Giới thiệu</a>
    <a class="toc__item" href="#" tabindex="-1">Cài đặt</a>
    <a class="toc__item" href="#" tabindex="-1">Cách dùng</a>
    <a class="toc__item" href="#" tabindex="-1">Tổng kết</a>
  </nav>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;
$color: $subject-blue;                              // 활성 알약 색
$row: 36px;                                         // 목차 한 줄 높이 (알약 이동 간격)

@include stage($stage-paper);

.toc {
  position: relative;
  display: flex;
  flex-direction: column;
  width: min(220px, 80vw);
}

// 옅은 색 칩이라야 알약이 두 줄에 걸치는 전환 중에도 글자 대비가 안 깨진다 (진한 배경 + 어두운 글자는 전환 중 대비가 무너진다)
.toc__pill {
  position: absolute;
  left: 0; top: 0;
  width: 100%; height: $row;
  border-radius: $r-sm;
  background: rgba(47, 109, 246, .14);
  border-left: 3px solid $color;
  z-index: 0;
  transform: translateY(0);
}

.toc__item {
  position: relative;
  z-index: 1;
  height: $row;
  display: flex;
  align-items: center;
  padding: 0 $sp-3;
  font-weight: 600;
  font-size: 14px;
  line-height: 1;
  font-family: inherit;
  color: $subject-ink;
  text-decoration: none;
}

// ── 실제 사용: 흔히 IntersectionObserver 로 지금 보이는 제목을 찾아 --active 를 바꾼다.
// 구간 크기가 고르면 animation-timeline: scroll(root) 로도 같은 스텝 키프레임을 쓸 수 있다 ──

// ── 데모: 알약이 항목 네 개를 순서대로 미끄러지듯 오르내린다 ──
// (구간마다 바로 다음 값으로 점프하면 프레임 사이 변화가 한두 장뿐이다 — 구간의 절반을 이동에 쓴다)
.toc.is-demo .toc__pill { animation: move $duration ease-in-out infinite; }
@keyframes move {
  0%, 10%    { transform: translateY(0); }
  25%, 35%   { transform: translateY($row); }
  50%, 60%   { transform: translateY($row * 2); }
  75%, 85%   { transform: translateY($row * 3); }
  100%       { transform: translateY(0); }
}

@media (prefers-reduced-motion: reduce) {
  .toc.is-demo .toc__pill { animation: none !important; }
}

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);
}

.toc {
  position: relative;
  display: flex;
  flex-direction: column;
  width: min(220px, 80vw);
}

.toc__pill {
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: 36px;
  border-radius: 8px;
  background: rgba(47, 109, 246, 0.14);
  border-left: 3px solid #2f6df6;
  z-index: 0;
  transform: translateY(0);
}

.toc__item {
  position: relative;
  z-index: 1;
  height: 36px;
  display: flex;
  align-items: center;
  padding: 0 12px;
  font-weight: 600;
  font-size: 14px;
  line-height: 1;
  font-family: inherit;
  color: #17141a;
  text-decoration: none;
}

.toc.is-demo .toc__pill {
  animation: move 2s ease-in-out infinite;
}

@keyframes move {
  0%, 10% {
    transform: translateY(0);
  }
  25%, 35% {
    transform: translateY(36px);
  }
  50%, 60% {
    transform: translateY(72px);
  }
  75%, 85% {
    transform: translateY(108px);
  }
  100% {
    transform: translateY(0);
  }
}
@media (prefers-reduced-motion: reduce) {
  .toc.is-demo .toc__pill {
    animation: none !important;
  }
}

import { useEffect, useState } from "react";
import styles from "./TocHighlight.module.scss";

export type TocItem = { id: string; label: string };
export type TocHighlightProps = {
  items: TocItem[];
  /** 알약 색 */
  color?: string;
  /** 한 줄 높이 (px) */
  row?: number;
};

// 실제 쓰임: IntersectionObserver 로 지금 보이는 제목을 찾아 알약을 그 줄로 옮긴다.
export default function TocHighlight({ items, color = "#2f6df6", row = 36 }: TocHighlightProps) {
  const [active, setActive] = useState(0);

  useEffect(() => {
    const els = items.map((it) => document.getElementById(it.id)).filter(Boolean) as HTMLElement[];
    const io = new IntersectionObserver(
      (entries) => {
        const top = entries.filter((e) => e.isIntersecting).sort((a, b) => b.intersectionRatio - a.intersectionRatio)[0];
        if (top) setActive(els.indexOf(top.target as HTMLElement));
      },
      { threshold: [0.3, 0.6] }
    );
    els.forEach((el) => io.observe(el));
    return () => io.disconnect();
  }, [items]);

  return (
    <nav className={styles.toc} aria-label="Contents" style={{ width: 220 }}>
      <span className={styles.pill} style={{ borderLeftColor: color, height: row, transform: `translateY(${active * row}px)` }} />
      {items.map((it) => (
        <a key={it.id} href={`#${it.id}`} className={styles.item} style={{ height: row }}>
          {it.label}
        </a>
      ))}
    </nav>
  );
}

<main class="stage">
  <p class="time is-demo" role="status">
    <span class="time__label">còn</span>
    <span class="time__num" aria-hidden="true"></span>
    <span class="time__label">phút</span>
  </p>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$total: 12;                                         // 전체 예상 분 (두 자릿수로 시작해야 자릿수가 바뀌는 순간도 보인다)
$color: $subject-cream;                             // 숫자 색
$duration: $dur-loop;

@include stage($stage-ink);

@property --min {
  syntax: '<integer>';
  initial-value: #{$total};
  inherits: false;
}

.time {
  display: flex;
  align-items: baseline;
  gap: $sp-2;
  margin: 0;
  color: rgba(255, 255, 255, .7);
  font-weight: 600;
  font-size: 16px;
  line-height: 1;
  font-family: inherit;
}

.time__num {
  --min: #{$total};
  counter-reset: min var(--min);
  color: $color;
  font-weight: 800;
  font-size: clamp(34px, 11vw, 46px);
  line-height: 1;
  font-family: inherit;
  font-variant-numeric: tabular-nums;

  &::before { content: counter(min); }

  // 실제 사용: 남은 분수 = 전체 분수 × (1 − 스크롤 진행률)
  @supports (animation-timeline: scroll()) {
    animation: count-down linear both;
    animation-timeline: scroll(root);
  }
}
@keyframes count-down { from { --min: #{$total}; } to { --min: 0; } }

.time.is-demo .time__num { animation: count-down-loop $duration linear infinite; }
@keyframes count-down-loop {
  0%   { --min: #{$total}; }
  92%  { --min: 0; }
  100% { --min: 0; }
}

@media (prefers-reduced-motion: reduce) {
  .time__num, .time.is-demo .time__num { animation: none !important; --min: 0; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

@property --min {
  syntax: "<integer>";
  initial-value: 12;
  inherits: false;
}
.time {
  display: flex;
  align-items: baseline;
  gap: 8px;
  margin: 0;
  color: rgba(255, 255, 255, 0.7);
  font-weight: 600;
  font-size: 16px;
  line-height: 1;
  font-family: inherit;
}

.time__num {
  --min: 12;
  counter-reset: min var(--min);
  color: #fff7e6;
  font-weight: 800;
  font-size: clamp(34px, 11vw, 46px);
  line-height: 1;
  font-family: inherit;
  font-variant-numeric: tabular-nums;
}
.time__num::before {
  content: counter(min);
}
@supports (animation-timeline: scroll()) {
  .time__num {
    animation: count-down linear both;
    animation-timeline: scroll(root);
  }
}

@keyframes count-down {
  from {
    --min: 12;
  }
  to {
    --min: 0;
  }
}
.time.is-demo .time__num {
  animation: count-down-loop 2s linear infinite;
}

@keyframes count-down-loop {
  0% {
    --min: 12;
  }
  92% {
    --min: 0;
  }
  100% {
    --min: 0;
  }
}
@media (prefers-reduced-motion: reduce) {
  .time__num, .time.is-demo .time__num {
    animation: none !important;
    --min: 0;
  }
}

import { useEffect, useState } from "react";
import styles from "./ReadingTime.module.scss";

export type ReadingTimeProps = {
  /** 전체 예상 분 */
  totalMinutes: number;
  /** 숫자 색 */
  color?: string;
};

// 실제 쓰임: 남은 분 = 전체 분 × (1 − 스크롤 진행률).
export default function ReadingTime({ totalMinutes, color = "#fff7e6" }: ReadingTimeProps) {
  const [left, setLeft] = useState(totalMinutes);

  useEffect(() => {
    const onScroll = () => {
      const max = document.documentElement.scrollHeight - window.innerHeight;
      const p = max > 0 ? Math.min(1, window.scrollY / max) : 0;
      setLeft(Math.max(0, Math.round(totalMinutes * (1 - p))));
    };
    onScroll();
    window.addEventListener("scroll", onScroll, { passive: true });
    return () => window.removeEventListener("scroll", onScroll);
  }, [totalMinutes]);

  return (
    <p className={styles.time} role="status">
      <span>left</span>
      <span className={styles.num} style={{ color }}>{left}</span>
      <span>min</span>
    </p>
  );
}