04リキッド充填（波の水面）

<main class="stage">
  <button class="liq is-demo" type="button">
    <span class="liq__wave" aria-hidden="true"></span>
    <span class="liq__label">カートに入れる</span>
  </button>
</main>

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

// 변형은 이 세 줄만 바꾼다
$duration: $dur-loop;
$easing:   $ease-spring;
$color:    $subject-mint;

@include stage($stage-yellow);

.liq {
  position: relative;
  overflow: hidden;
  isolation: isolate;
  border: 0;
  cursor: pointer;
  padding: $sp-4 $sp-8;
  border-radius: $r-pill;
  background: $subject-cream;
  box-shadow: inset 0 0 0 2px $subject-ink;
  color: $subject-ink;
  font-family: inherit;
  font-size: clamp(15px, 4.5vw, 19px);
  font-weight: 800;
}

// 수면이 평평하지 않은 이유: 완전한 원이 아니라 네 모서리를 42% 둥글린 정사각형을 통째로 돌린다
.liq__wave {
  position: absolute;
  left: 50%;
  bottom: 0;
  width: 260px;
  height: 260px;
  border-radius: 42%;
  background: $color;
  transform: translate(-50%, 100%);
}

.liq__label { position: relative; }

.liq.is-demo .liq__wave { animation: liq-rise $duration $easing infinite; }

// rotate 가 0deg 에서 360deg 로 끝나 마지막 프레임과 첫 프레임의 그림이 같다
@keyframes liq-rise {
  0%   { transform: translate(-50%, 100%) rotate(0deg); }
  52%  { transform: translate(-50%, 68%) rotate(180deg); }
  66%  { transform: translate(-50%, 68%) rotate(230deg); }
  100% { transform: translate(-50%, 100%) rotate(360deg); }
}

@media (prefers-reduced-motion: reduce) {
  .liq.is-demo .liq__wave { animation: none; transform: translate(-50%, 68%); }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.liq {
  position: relative;
  overflow: hidden;
  isolation: isolate;
  border: 0;
  cursor: pointer;
  padding: 16px 32px;
  border-radius: 999px;
  background: #fff7e6;
  box-shadow: inset 0 0 0 2px #17141a;
  color: #17141a;
  font-family: inherit;
  font-size: clamp(15px, 4.5vw, 19px);
  font-weight: 800;
}

.liq__wave {
  position: absolute;
  left: 50%;
  bottom: 0;
  width: 260px;
  height: 260px;
  border-radius: 42%;
  background: #4cd4a6;
  transform: translate(-50%, 100%);
}

.liq__label {
  position: relative;
}

.liq.is-demo .liq__wave {
  animation: liq-rise 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@keyframes liq-rise {
  0% {
    transform: translate(-50%, 100%) rotate(0deg);
  }
  52% {
    transform: translate(-50%, 68%) rotate(180deg);
  }
  66% {
    transform: translate(-50%, 68%) rotate(230deg);
  }
  100% {
    transform: translate(-50%, 100%) rotate(360deg);
  }
}
@media (prefers-reduced-motion: reduce) {
  .liq.is-demo .liq__wave {
    animation: none;
    transform: translate(-50%, 68%);
  }
}

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

export type LiquidFillButtonProps = {
  label?: string;
  duration?: number;
  easing?: string;
  color?: string;
};

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

export default function LiquidFillButton({
  label = "Add to cart",
  duration = 2000,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#4cd4a6",
}: LiquidFillButtonProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  return (
    <button type="button" className={styles.liq} style={vars}>
      <span className={styles.wave} aria-hidden="true" />
      <span className={styles.label}>{label}</span>
    </button>
  );
}