02눌림 축소 + 그림자 감소

<main class="stage">
  <button class="btn is-demo" type="button">구매하기</button>
</main>

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

$duration: $dur-quick;                            // 눌렸다가 돌아오는 시간 (바운스 없음)
$easing: $ease-out;
$color: $subject-ink;                             // 버튼 색

@include stage($stage-yellow);

.btn {
  position: relative;
  border: 0;
  border-radius: $r-control;
  padding: 18px 40px;
  font-weight: 600; font-size: 18px; line-height: 1; font-family: inherit;
  color: $subject-cream;
  background: $color;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  touch-action: manipulation;                     // 더블탭 확대·300ms 지연 제거
  box-shadow: $shadow-raised;
  transform: scale(1);
  transition: transform $duration $easing, box-shadow $duration $easing;

  // 규칙8 한 겹: 눌리는 순간 버튼 바깥으로 두 겹 링이 서로 다른 속도로 불규칙하게 번지다 감쇠
  &::after {
    content: "";
    position: absolute;
    inset: -2px;
    border-radius: inherit;
    box-shadow: 0 0 0 0 rgba($subject-blue, .5), 0 0 0 0 rgba($subject-blue, .3);
    opacity: 0;
    pointer-events: none;
  }
}

.btn:active {
  transform: scale(.96);
  box-shadow: $shadow-press;
}
.btn:active::after {
  animation: ripple-wave $dur-enter $easing;
}

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

.btn.is-demo { animation: press-loop $dur-loop $easing infinite; }
.btn.is-demo::after { animation: ripple-loop $dur-loop $easing infinite; }

@keyframes press-loop {
  0%, 20%  { transform: scale(1);    box-shadow: $shadow-raised; }
  45%, 60% { transform: scale(.96);  box-shadow: $shadow-press; }
  100%     { transform: scale(1);    box-shadow: $shadow-raised; }
}

@keyframes ripple-wave {
  0%   { box-shadow: 0 0 0 0 rgba($subject-blue, .55), 0 0 0 0 rgba($subject-blue, .34); opacity: 1; }
  20%  { box-shadow: 0 0 0 8px rgba($subject-blue, .55), 0 0 0 3px rgba($subject-blue, .34); opacity: 1; }
  55%  { box-shadow: 0 0 0 14px rgba($subject-blue, .3), 0 0 0 9px rgba($subject-blue, .2); opacity: .9; }
  85%  { box-shadow: 0 0 0 16px rgba($subject-blue, .06), 0 0 0 12px rgba($subject-blue, .04); opacity: .2; }
  100% { box-shadow: 0 0 0 16px rgba($subject-blue, 0), 0 0 0 12px rgba($subject-blue, 0); opacity: 0; }
}

@keyframes ripple-loop {
  0%, 40%   { box-shadow: 0 0 0 0 rgba($subject-blue, .55), 0 0 0 0 rgba($subject-blue, .34); opacity: 1; }
  46%       { box-shadow: 0 0 0 8px rgba($subject-blue, .55), 0 0 0 3px rgba($subject-blue, .34); opacity: 1; }
  53%       { box-shadow: 0 0 0 14px rgba($subject-blue, .3), 0 0 0 9px rgba($subject-blue, .2); opacity: .9; }
  58%       { box-shadow: 0 0 0 16px rgba($subject-blue, .06), 0 0 0 12px rgba($subject-blue, .04); opacity: .2; }
  63%, 100% { box-shadow: 0 0 0 16px rgba($subject-blue, 0), 0 0 0 12px rgba($subject-blue, 0); opacity: 0; }
}

@media (prefers-reduced-motion: reduce) {
  .btn { transition: none; }
  .btn::after { animation: none !important; opacity: 0; }
  .btn.is-demo { animation: none; box-shadow: $shadow-press; }
}

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);
}

.btn {
  position: relative;
  border: 0;
  border-radius: 12px;
  padding: 18px 40px;
  font-weight: 600;
  font-size: 18px;
  line-height: 1;
  font-family: inherit;
  color: #fff7e6;
  background: #17141a;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  touch-action: manipulation;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  transform: scale(1);
  transition: transform 220ms ease-out, box-shadow 220ms ease-out;
}
.btn::after {
  content: "";
  position: absolute;
  inset: -2px;
  border-radius: inherit;
  box-shadow: 0 0 0 0 rgba(47, 109, 246, 0.5), 0 0 0 0 rgba(47, 109, 246, 0.3);
  opacity: 0;
  pointer-events: none;
}

.btn:active {
  transform: scale(0.96);
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
}

.btn:active::after {
  animation: ripple-wave 600ms ease-out;
}

.btn:focus-visible {
  outline: 3px solid #2f6df6;
  outline-offset: 3px;
}

.btn.is-demo {
  animation: press-loop 2s ease-out infinite;
}

.btn.is-demo::after {
  animation: ripple-loop 2s ease-out infinite;
}

@keyframes press-loop {
  0%, 20% {
    transform: scale(1);
    box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  }
  45%, 60% {
    transform: scale(0.96);
    box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  }
  100% {
    transform: scale(1);
    box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  }
}
@keyframes ripple-wave {
  0% {
    box-shadow: 0 0 0 0 rgba(47, 109, 246, 0.55), 0 0 0 0 rgba(47, 109, 246, 0.34);
    opacity: 1;
  }
  20% {
    box-shadow: 0 0 0 8px rgba(47, 109, 246, 0.55), 0 0 0 3px rgba(47, 109, 246, 0.34);
    opacity: 1;
  }
  55% {
    box-shadow: 0 0 0 14px rgba(47, 109, 246, 0.3), 0 0 0 9px rgba(47, 109, 246, 0.2);
    opacity: 0.9;
  }
  85% {
    box-shadow: 0 0 0 16px rgba(47, 109, 246, 0.06), 0 0 0 12px rgba(47, 109, 246, 0.04);
    opacity: 0.2;
  }
  100% {
    box-shadow: 0 0 0 16px rgba(47, 109, 246, 0), 0 0 0 12px rgba(47, 109, 246, 0);
    opacity: 0;
  }
}
@keyframes ripple-loop {
  0%, 40% {
    box-shadow: 0 0 0 0 rgba(47, 109, 246, 0.55), 0 0 0 0 rgba(47, 109, 246, 0.34);
    opacity: 1;
  }
  46% {
    box-shadow: 0 0 0 8px rgba(47, 109, 246, 0.55), 0 0 0 3px rgba(47, 109, 246, 0.34);
    opacity: 1;
  }
  53% {
    box-shadow: 0 0 0 14px rgba(47, 109, 246, 0.3), 0 0 0 9px rgba(47, 109, 246, 0.2);
    opacity: 0.9;
  }
  58% {
    box-shadow: 0 0 0 16px rgba(47, 109, 246, 0.06), 0 0 0 12px rgba(47, 109, 246, 0.04);
    opacity: 0.2;
  }
  63%, 100% {
    box-shadow: 0 0 0 16px rgba(47, 109, 246, 0), 0 0 0 12px rgba(47, 109, 246, 0);
    opacity: 0;
  }
}
@media (prefers-reduced-motion: reduce) {
  .btn {
    transition: none;
  }
  .btn::after {
    animation: none !important;
    opacity: 0;
  }
  .btn.is-demo {
    animation: none;
    box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  }
}

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

export type PressShrinkButtonProps = {
  label: string;
  /** 눌렸다가 돌아오는 시간, 바운스 없음 (기본 220ms) */
  duration?: number;
  easing?: string;
  color?: string;
};

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

export default function PressShrinkButton({
  label,
  duration = 220,
  easing = "ease-out",
  color = "#17141a",
}: PressShrinkButtonProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  return (
    <button type="button" className={styles.btn} style={vars}>
      {label}
    </button>
  );
}