08Logo bar — a row whose horizontal offset value keeps growing without a seam

<main class="stage" id="stage">
  <section class="marquee-wrap">
    <p class="marquee__caption">Partners we work with</p>
    <div class="marquee">
      <div class="marquee__track is-demo">
        <span class="logo logo--a">BRAND A</span>
        <span class="logo logo--b">BRAND B</span>
        <span class="logo logo--c">BRAND C</span>
        <span class="logo logo--d">BRAND D</span>
        <span class="logo logo--a" aria-hidden="true">BRAND A</span>
        <span class="logo logo--b" aria-hidden="true">BRAND B</span>
        <span class="logo logo--c" aria-hidden="true">BRAND C</span>
        <span class="logo logo--d" aria-hidden="true">BRAND D</span>
      </div>
    </div>
  </section>
</main>

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

$duration: 9s;
$easing: linear;
$color: $subject-blue-deep;

@include stage($stage-paper);

.marquee-wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: $sp-5;
  width: 100%;
}

.marquee__caption {
  margin: 0;
  color: $subject-ink;
  font-weight: 600;
  font-size: 12px;
  letter-spacing: 0.02em;
}

.marquee {
  overflow: hidden;
  width: min(92vw, 360px);
  -webkit-mask-image: linear-gradient(to right, transparent, #000 12%, #000 88%, transparent);
  mask-image: linear-gradient(to right, transparent, #000 12%, #000 88%, transparent);
}

.marquee__track {
  display: flex;
  width: max-content;
  will-change: transform;
}

.marquee__track.is-demo {
  animation: scroll $duration $easing infinite;
}

.logo {
  margin-right: $sp-8;
  color: $color;
  font-weight: 700;
  font-size: 15px;
  letter-spacing: 0.03em;
  white-space: nowrap;
}

@keyframes scroll {
  from { transform: translateX(0); }
  to { transform: translateX(-50%); }
}

@media (max-width: 340px) {
  .logo { font-size: 13px; margin-right: $sp-6; }
}

@media (prefers-reduced-motion: reduce) {
  .marquee__track.is-demo { animation: none; }
}

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);
}

.marquee-wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 20px;
  width: 100%;
}

.marquee__caption {
  margin: 0;
  color: #17141a;
  font-weight: 600;
  font-size: 12px;
  letter-spacing: 0.02em;
}

.marquee {
  overflow: hidden;
  width: min(92vw, 360px);
  -webkit-mask-image: linear-gradient(to right, transparent, #000 12%, #000 88%, transparent);
  mask-image: linear-gradient(to right, transparent, #000 12%, #000 88%, transparent);
}

.marquee__track {
  display: flex;
  width: max-content;
  will-change: transform;
}

.marquee__track.is-demo {
  animation: scroll 9s linear infinite;
}

.logo {
  margin-right: 32px;
  color: #0a4fe8;
  font-weight: 700;
  font-size: 15px;
  letter-spacing: 0.03em;
  white-space: nowrap;
}

@keyframes scroll {
  from {
    transform: translateX(0);
  }
  to {
    transform: translateX(-50%);
  }
}
@media (max-width: 340px) {
  .logo {
    font-size: 13px;
    margin-right: 24px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .marquee__track.is-demo {
    animation: none;
  }
}

import styles from "./LogoBar.module.scss";

// 트랙을 통째로 복제해 이어 붙이고, 가로 이동 값(translateX)이 계속 늘어나다 -50% 지점에서 이음매 없이 되돌아간다.
// 계산 겹: 가로 이동 값 -> translateX 보간(무한 반복). 리스너 없음(자동 재생).
const LOGOS = ["BRAND A", "BRAND B", "BRAND C", "BRAND D"];

export default function LogoBar() {
  const track = [...LOGOS, ...LOGOS];

  return (
    <main className={styles.stage}>
      <section className={styles["marquee-wrap"]}>
        <p className={styles.marquee__caption}>함께하는 파트너</p>
        <div className={styles.marquee}>
          <div className={`${styles.marquee__track} ${styles["is-demo"]}`}>
            {track.map((name, i) => (
              <span key={`${name}-${i}`} className={styles.logo} aria-hidden={i >= LOGOS.length}>
                {name}
              </span>
            ))}
          </div>
        </div>
      </section>
    </main>
  );
}