01Nút gradient kẹo chảy

<main class="stage is-demo">
  <button class="btn" type="button">
    <span class="btn__bg" aria-hidden="true"></span>
    <span class="btn__label">Tham gia ngay</span>
  </button>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;    // 2s — 그라데이션 한 주기
$easing: linear;         // 흐름은 일정한 속도로
$color: #ff9ecb;         // 캔디 핑크 (시작색)

// 한 주기 240px — 세 색이 6px 여백을 두고 스며든다
$candy-b: #d9d4ea;       // 바이올렛
$candy-c: #cddfe6;       // 스카이

@include stage($stage-ink);

.btn {
  box-sizing: border-box;
  position: relative;
  width: 240px;
  height: 64px;
  border: none;
  border-radius: $r-pill;
  color: $subject-ink;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  font-weight: 700;
  font-size: 18px;
  cursor: pointer;
  overflow: hidden;       // 3배 그라데이션이 밖으로 새지 않게
  box-shadow: $shadow-raised;
  transition: transform $dur-quick $ease-spring, box-shadow $dur-quick $ease-spring;
}

// 3배 폭 그라데이션 층 — 한 주기(240px)씩 translateX 로 흐른다
.btn__bg {
  position: absolute;
  top: 0; bottom: 0; left: 0;
  width: 720px;
  background: repeating-linear-gradient(to right,
    $color 0 58px, $candy-b 64px 118px, $candy-c 124px 178px, $color 184px 240px);
}

.btn__label { position: relative; z-index: 1; }

// 실사용: 마우스를 올리면 살짝 들리고 흐름은 그대로
.btn:hover { transform: translateY(-2px); box-shadow: 0 18px 28px rgba(23, 20, 26, .4); }

.btn:focus-visible { outline: 3px solid $stage-yellow; outline-offset: 4px; }

// 격자 미리보기: transform 만 이동 (레이아웃 재계산 없음)
.stage.is-demo .btn__bg {
  animation: gradient-flow $duration $easing infinite;
}

@keyframes gradient-flow {
  0%   { transform: translateX(0); }
  100% { transform: translateX(-240px); }   // 정확히 한 주기 = 이음새 없는 루프
}

@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .btn__bg { animation: none; transform: translateX(-120px); }
}

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);
}

.btn {
  box-sizing: border-box;
  position: relative;
  width: 240px;
  height: 64px;
  border: none;
  border-radius: 999px;
  color: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  font-weight: 700;
  font-size: 18px;
  cursor: pointer;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  transition: transform 220ms cubic-bezier(0.2, 0.8, 0.2, 1), box-shadow 220ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.btn__bg {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  width: 720px;
  background: repeating-linear-gradient(to right, #ff9ecb 0 58px, #d9d4ea 64px 118px, #cddfe6 124px 178px, #ff9ecb 184px 240px);
}

.btn__label {
  position: relative;
  z-index: 1;
}

.btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 18px 28px rgba(23, 20, 26, 0.4);
}

.btn:focus-visible {
  outline: 3px solid #ffd23f;
  outline-offset: 4px;
}

.stage.is-demo .btn__bg {
  animation: gradient-flow 2s linear infinite;
}

@keyframes gradient-flow {
  0% {
    transform: translateX(0);
  }
  100% {
    transform: translateX(-240px);
  }
}
@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .btn__bg {
    animation: none;
    transform: translateX(-120px);
  }
}

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

export type GradientFlowButtonProps = {
  duration?: number;
  easing?: string;
  color?: string;
  candyB?: string;
  candyC?: string;
  label?: string;
};

export default function GradientFlowButton({
  duration = 2000,
  easing = "linear",
  color = "#ff9ecb",
  candyB = "#a78bfa",
  candyC = "#7cd8ff",
  label = "멤버 되기",
}: GradientFlowButtonProps) {
  const vars: CSSProperties = {
    "--duration": `${duration}ms`,
    "--easing": easing,
    "--color": color,
    "--candy-b": candyB,
    "--candy-c": candyC,
  } as CSSProperties;
  return (
    <button className={styles.btn} style={vars} type="button">
      <span className={styles.bg} aria-hidden="true" />
      <span className={styles.label}>{label}</span>
    </button>
  );
}