04端をマスクでフェード

<main class="stage">
  <div class="marquee">
    <div class="marquee__track">
      <span class="marquee__chip">01</span>
      <span class="marquee__chip">02</span>
      <span class="marquee__chip">03</span>
      <span class="marquee__chip">04</span>
      <span class="marquee__chip">05</span>
      <span class="marquee__chip" aria-hidden="true">01</span>
      <span class="marquee__chip" aria-hidden="true">02</span>
      <span class="marquee__chip" aria-hidden="true">03</span>
      <span class="marquee__chip" aria-hidden="true">04</span>
      <span class="marquee__chip" aria-hidden="true">05</span>
    </div>
  </div>
</main>

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

$duration: $dur-loop;
$easing: linear;
$color: $subject-ink;

@include stage($stage-paper);

.marquee {
  width: min(320px, 84vw);
  overflow: hidden;
  mask-image: linear-gradient(to right, transparent, #000 14%, #000 86%, transparent);
  -webkit-mask-image: linear-gradient(to right, transparent, #000 14%, #000 86%, transparent);
}
.marquee__track {
  display: flex;
  width: max-content;
  animation: marquee-scroll $duration $easing infinite;
}
.marquee__chip {
  margin-right: 18px;   // 트랙의 gap 대신 — 세트 폭이 정확히 절반이 되어 -50% 이음새가 0px 이 된다
  flex-shrink: 0;
  display: grid;
  place-items: center;
  width: 44px;
  height: 44px;
  border-radius: $r-control;
  border: 2px solid $color;
  color: $color;
  font-weight: 700; font-size: 14px; line-height: 1; font-family: inherit;
}

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

@media (prefers-reduced-motion: reduce) {
  .marquee__track { animation: none; transform: translateX(0); }
}

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 {
  width: min(320px, 84vw);
  overflow: hidden;
  mask-image: linear-gradient(to right, transparent, #000 14%, #000 86%, transparent);
  -webkit-mask-image: linear-gradient(to right, transparent, #000 14%, #000 86%, transparent);
}

.marquee__track {
  display: flex;
  width: max-content;
  animation: marquee-scroll 2s linear infinite;
}

.marquee__chip {
  margin-right: 18px;
  flex-shrink: 0;
  display: grid;
  place-items: center;
  width: 44px;
  height: 44px;
  border-radius: 12px;
  border: 2px solid #17141a;
  color: #17141a;
  font-weight: 700;
  font-size: 14px;
  line-height: 1;
  font-family: inherit;
}

@keyframes marquee-scroll {
  from {
    transform: translateX(0);
  }
  to {
    transform: translateX(-50%);
  }
}
@media (prefers-reduced-motion: reduce) {
  .marquee__track {
    animation: none;
    transform: translateX(0);
  }
}

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

export type FadeEdgeMarqueeProps = {
  items?: string[];
  duration?: number;
  easing?: string;
  color?: string;
};

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

export default function FadeEdgeMarquee({
  items = ["01", "02", "03", "04", "05"],
  duration = 12000,
  easing = "linear",
  color = "#17141a",
}: FadeEdgeMarqueeProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  return (
    <div className={styles.marquee} style={vars}>
      <div className={styles.track}>
        {items.map((it) => (
          <span key={it} className={styles.chip}>{it}</span>
        ))}
        {items.map((it) => (
          <span key={"dup-" + it} className={styles.chip} aria-hidden="true">{it}</span>
        ))}
      </div>
    </div>
  );
}