03Gooey blob button

<main class="stage is-demo">
  <button class="btn" type="button"><span class="btn__label">Add</span></button>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-loop;   // 2s — 부풀기 한 주기
$easing: $ease-pop;     // 튕기듯 말랑하게
$color: #bcded4;        // 민트

@include stage($stage-orange);

.btn {
  box-sizing: border-box;
  position: relative;
  width: 240px;
  height: 64px;
  border: none;
  border-radius: $r-pill;
  background: $color;
  color: $subject-ink;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  font-weight: 700;
  font-size: 18px;
  cursor: pointer;
}

// 라벨은 블롭 위에
.btn__label { position: relative; z-index: 1; }

// 좌우 블롭 — 버튼과 같은 색이라 윤곽이 합쳐져 말랑하게 늘어나 보인다
.btn::before,
.btn::after {
  content: "";
  position: absolute;
  top: 50%;
  width: 56px;
  height: 56px;
  border-radius: 50%;
  background: $color;
  transform: translateY(-50%) scale(.3);
}
.btn::before { left: -4px; }
.btn::after  { right: -4px; }

// 실사용: 올리면 좌우로 부풀고, 크기가 커질수록 말랑함이 커진다
.btn:hover::before { transform: translateY(-50%) scale(1.25) translateX(-8px); }
.btn:hover::after  { transform: translateY(-50%) scale(1.25) translateX(8px); }
.btn::before, .btn::after { transition: transform $dur-base $easing; }

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

// 격자 미리보기: 말랑-주물럭 루프
.stage.is-demo .btn::before { animation: blob-l $duration $easing infinite; }
.stage.is-demo .btn::after  { animation: blob-r $duration $easing infinite; }

@keyframes blob-l {
  0%, 12%  { transform: translateY(-50%) scale(.3); }
  40%      { transform: translateY(-50%) scale(1.3) translateX(-8px); }
  68%, 82% { transform: translateY(-50%) scale(1.15) translateX(-4px); }
  100%     { transform: translateY(-50%) scale(.3); }
}
@keyframes blob-r {
  0%, 12%  { transform: translateY(-50%) scale(.3); }
  40%      { transform: translateY(-50%) scale(1.3) translateX(8px); }
  68%, 82% { transform: translateY(-50%) scale(1.15) translateX(4px); }
  100%     { transform: translateY(-50%) scale(.3); }
}

@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .btn::before, .stage.is-demo .btn::after { animation: none; }
}

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);
}

.btn {
  box-sizing: border-box;
  position: relative;
  width: 240px;
  height: 64px;
  border: none;
  border-radius: 999px;
  background: #bcded4;
  color: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  font-weight: 700;
  font-size: 18px;
  cursor: pointer;
}

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

.btn::before,
.btn::after {
  content: "";
  position: absolute;
  top: 50%;
  width: 56px;
  height: 56px;
  border-radius: 50%;
  background: #bcded4;
  transform: translateY(-50%) scale(0.3);
}

.btn::before {
  left: -4px;
}

.btn::after {
  right: -4px;
}

.btn:hover::before {
  transform: translateY(-50%) scale(1.25) translateX(-8px);
}

.btn:hover::after {
  transform: translateY(-50%) scale(1.25) translateX(8px);
}

.btn::before, .btn::after {
  transition: transform 300ms cubic-bezier(0.2, 1.4, 0.4, 1);
}

.btn:focus-visible {
  outline: 3px solid #17141a;
  outline-offset: 4px;
}

.stage.is-demo .btn::before {
  animation: blob-l 2s cubic-bezier(0.2, 1.4, 0.4, 1) infinite;
}

.stage.is-demo .btn::after {
  animation: blob-r 2s cubic-bezier(0.2, 1.4, 0.4, 1) infinite;
}

@keyframes blob-l {
  0%, 12% {
    transform: translateY(-50%) scale(0.3);
  }
  40% {
    transform: translateY(-50%) scale(1.3) translateX(-8px);
  }
  68%, 82% {
    transform: translateY(-50%) scale(1.15) translateX(-4px);
  }
  100% {
    transform: translateY(-50%) scale(0.3);
  }
}
@keyframes blob-r {
  0%, 12% {
    transform: translateY(-50%) scale(0.3);
  }
  40% {
    transform: translateY(-50%) scale(1.3) translateX(8px);
  }
  68%, 82% {
    transform: translateY(-50%) scale(1.15) translateX(4px);
  }
  100% {
    transform: translateY(-50%) scale(0.3);
  }
}
@media (prefers-reduced-motion: reduce) {
  .stage.is-demo .btn::before, .stage.is-demo .btn::after {
    animation: none;
  }
}

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

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

export default function GooeyBlobButton({
  duration = 300,
  easing = "cubic-bezier(.2, 1.4, .4, 1)",
  color = "#7fe3c4",
  label = "담기",
}: GooeyBlobButtonProps) {
  const vars: CSSProperties = { "--duration": `${duration}ms`, "--easing": easing, "--color": color } as CSSProperties;
  return (
    <button className={styles.btn} style={vars} type="button">
      <span className={styles.label}>{label}</span>
    </button>
  );
}