03ease-out-expo 곡선

<main class="stage is-demo">
  <div class="track">
    <span class="dot dot--start"></span>
    <span class="dot dot--end"></span>
    <div class="puck"></div>
  </div>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;                       // 2s
$easing: cubic-bezier(.16, 1, .3, 1);       // ease-out-expo — 첫 프레임부터 거의 다 이동해 있고, 나머지 구간은 아주 천천히 기어간다
$color: $subject-cream;

@include stage($stage-orange);

$track-w: 220px;
$puck-w: $sp-6;
$travel: $track-w - $puck-w;

.track {
  position: relative;
  width: $track-w;
  height: $sp-2;
}

.dot {
  position: absolute;
  top: 50%;
  width: $sp-2;
  height: $sp-2;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .3);
  transform: translate(-50%, -50%);
}
.dot--start { left: 0; }
.dot--end { left: $track-w; }

.puck {
  position: absolute;
  top: 50%;
  left: 0;
  width: $puck-w;
  height: $puck-w;
  border-radius: $r-pill;
  background: $color;
  box-shadow: $shadow-raised;
  transform: translate(0, -50%);
}

.stage.is-demo .puck {
  animation: move $duration $easing infinite alternate;
}

@keyframes move {
  from { transform: translate(0, -50%); }
  to   { transform: translate($travel, -50%); }
}

@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .puck { animation: none; transform: translate($travel, -50%); }
}

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);
}

.track {
  position: relative;
  width: 220px;
  height: 8px;
}

.dot {
  position: absolute;
  top: 50%;
  width: 8px;
  height: 8px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.3);
  transform: translate(-50%, -50%);
}

.dot--start {
  left: 0;
}

.dot--end {
  left: 220px;
}

.puck {
  position: absolute;
  top: 50%;
  left: 0;
  width: 24px;
  height: 24px;
  border-radius: 999px;
  background: #fff7e6;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  transform: translate(0, -50%);
}

.stage.is-demo .puck {
  animation: move 2s cubic-bezier(0.16, 1, 0.3, 1) infinite alternate;
}

@keyframes move {
  from {
    transform: translate(0, -50%);
  }
  to {
    transform: translate(196px, -50%);
  }
}
@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .puck {
    animation: none;
    transform: translate(196px, -50%);
  }
}

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

export type EaseOutExpoProps = {
  duration?: number;
  color?: string;
};

export default function EaseOutExpo({ duration = 2000, color = "#fff7e6" }: EaseOutExpoProps) {
  const vars: CSSProperties = { "--duration": `${duration}ms`, "--color": color } as CSSProperties;
  return (
    <div className={styles.stage} style={vars}>
      <div className={styles.track}>
        <span className={`${styles.dot} ${styles.dotStart}`} />
        <span className={`${styles.dot} ${styles.dotEnd}`} />
        <div className={styles.puck} />
      </div>
    </div>
  );
}