04Arbitrary-value scroll-timeline

<main class="stage">
  <div class="page">
    <p class="page__label">A progress bar that fills as you read</p>
    <div class="track"><div class="track__fill is-demo"></div></div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
// 실제 스크롤에 물리는 animation-timeline:scroll() 은 브라우저마다 지원이 갈려
// (편브리프 표 참고) 데모에서 쓰지 않는다 — 같은 진행률을 2초 루프로 안전하게 재현한다.
$duration: 2000ms;
$easing: linear;
$color: $subject-blue;

// ── 데모 무대 ──────────────────────────────────────────
@include stage($stage-paper);

.page {
  box-sizing: border-box;
  width: min(300px, 88vw);
}

.page__label {
  margin: 0 0 $sp-4;
  color: $subject-ink;
  font-weight: 600;
  font-size: clamp(13px, 3.6vw, 15px);
  line-height: 1.4;
  font-family: inherit;
}

.track {
  height: $sp-2;
  border-radius: $r-pill;
  background: rgba($subject-ink, .12);
  overflow: hidden;
}

.track__fill {
  height: 100%;
  border-radius: inherit;
  background: $color;
  transform-origin: left center; // 규칙8: 진행바 왼쪽 채움
  transform: scaleX(0);
}

// 데모: 진행률이 0→1 로 다 차고 나면 리셋해 2초마다 반복
.track__fill.is-demo {
  animation: fill-loop $duration $easing infinite;
}

@keyframes fill-loop {
  0%   { transform: scaleX(0); }
  90%  { transform: scaleX(1); }
  100% { transform: scaleX(1); }
}

// ── 접근성: 움직임 줄이기 설정이면 다 찬 상태로 고정 ──────
@media (prefers-reduced-motion: reduce) {
  .track__fill.is-demo { animation: none; 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: #ffffff;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.page {
  box-sizing: border-box;
  width: min(300px, 88vw);
}

.page__label {
  margin: 0 0 16px;
  color: #17141a;
  font-weight: 600;
  font-size: clamp(13px, 3.6vw, 15px);
  line-height: 1.4;
  font-family: inherit;
}

.track {
  height: 8px;
  border-radius: 999px;
  background: rgba(23, 20, 26, 0.12);
  overflow: hidden;
}

.track__fill {
  height: 100%;
  border-radius: inherit;
  background: #2f6df6;
  transform-origin: left center;
  transform: scaleX(0);
}

.track__fill.is-demo {
  animation: fill-loop 2000ms linear infinite;
}

@keyframes fill-loop {
  0% {
    transform: scaleX(0);
  }
  90% {
    transform: scaleX(1);
  }
  100% {
    transform: scaleX(1);
  }
}
@media (prefers-reduced-motion: reduce) {
  .track__fill.is-demo {
    animation: none;
    transform: scaleX(1);
  }
}

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

export type ArbitraryTimelineProgressProps = {
  label?: string;
  /** 진행률이 다 차는 시간, ms — 실제 scroll-timeline 대신 안전한 루프로 재현 */
  duration?: number;
  easing?: string;
  color?: string;
};

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

export default function ArbitraryTimelineProgress({
  label = "A progress bar that fills as you read",
  duration = 2000,
  easing = "linear",
  color = "#2f6df6",
}: ArbitraryTimelineProgressProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  return (
    <div className={styles.page} style={vars}>
      <p className={styles.page__label}>{label}</p>
      <div className={styles.track}>
        <div className={styles.track__fill} />
      </div>
    </div>
  );
}