03Touch-only :active via pointer: coarse

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

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

$duration: $dur-quick;
$easing: $ease-out;
$color: $subject-cream;                           // 버튼 색

@include stage($stage-orange);

.btn {
  position: relative;
  border: 0;
  border-radius: $r-control;
  padding: 18px 44px;
  font-weight: 600; font-size: 18px; line-height: 1; font-family: inherit;
  color: $stage-ink;
  background: $color;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  transition: background $duration $easing, color $duration $easing;

  // 규칙8 한 겹: 색 반전 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($subject-blue, .48), 0 0 0 0 rgba($subject-blue, .28);
    opacity: 0;
    pointer-events: none;
  }
}

// 실제 규칙: 호버가 없는(터치) 기기에서만 :active 배경을 준다.
// 마우스 기기는 이 블록을 아예 안 읽어서, 탭 뒤 색이 눌어붙는 일이 없다.
@media (hover: none) and (pointer: coarse) {
  .btn:active {
    background: $stage-ink;
    color: $color;
  }
  .btn:active::after {
    animation: ripple-wave $dur-enter $easing;
  }
}

// 데모용: 렌더 환경은 마우스 포인터로 잡히므로 위 미디어쿼리가 실제로 켜졌을 때의
// 모습을 .is-demo 로 강제 재생한다 (실제 터치 여부와 무관).
.btn.is-demo {
  animation: touch-active-loop $dur-loop $easing infinite;
}
.btn.is-demo::after {
  animation: ripple-loop $dur-loop $easing infinite;
}

@keyframes touch-active-loop {
  0%, 20%  { background: $subject-cream; color: $stage-ink; }
  50%, 75% { background: $stage-ink;     color: $subject-cream; }
  100%     { background: $subject-cream; color: $stage-ink; }
}

@keyframes ripple-wave {
  0%   { box-shadow: 0 0 0 0 rgba($subject-blue, .48), 0 0 0 0 rgba($subject-blue, .28); opacity: 1; }
  38%  { box-shadow: 0 0 0 10px rgba($subject-blue, .2), 0 0 0 4px rgba($subject-blue, .26); opacity: .74; }
  66%  { box-shadow: 0 0 0 17px rgba($subject-blue, .09), 0 0 0 11px rgba($subject-blue, .15); opacity: .36; }
  100% { box-shadow: 0 0 0 24px rgba($subject-blue, 0), 0 0 0 20px rgba($subject-blue, 0); opacity: 0; }
}

@keyframes ripple-loop {
  0%, 20%  { box-shadow: 0 0 0 0 rgba($subject-blue, .48), 0 0 0 0 rgba($subject-blue, .28); opacity: 1; }
  38%      { box-shadow: 0 0 0 10px rgba($subject-blue, .2), 0 0 0 4px rgba($subject-blue, .26); opacity: .74; }
  55%      { box-shadow: 0 0 0 17px rgba($subject-blue, .09), 0 0 0 11px rgba($subject-blue, .15); opacity: .36; }
  75%, 100% { box-shadow: 0 0 0 24px rgba($subject-blue, 0), 0 0 0 20px rgba($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; }
}

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 {
  position: relative;
  border: 0;
  border-radius: 12px;
  padding: 18px 44px;
  font-weight: 600;
  font-size: 18px;
  line-height: 1;
  font-family: inherit;
  color: #17141a;
  background: #fff7e6;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  transition: background 220ms ease-out, color 220ms ease-out;
}
.btn::after {
  content: "";
  position: absolute;
  inset: -2px;
  border-radius: inherit;
  box-shadow: 0 0 0 0 rgba(47, 109, 246, 0.48), 0 0 0 0 rgba(47, 109, 246, 0.28);
  opacity: 0;
  pointer-events: none;
}

@media (hover: none) and (pointer: coarse) {
  .btn:active {
    background: #17141a;
    color: #fff7e6;
  }
  .btn:active::after {
    animation: ripple-wave 600ms ease-out;
  }
}
.btn.is-demo {
  animation: touch-active-loop 2s ease-out infinite;
}

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

@keyframes touch-active-loop {
  0%, 20% {
    background: #fff7e6;
    color: #17141a;
  }
  50%, 75% {
    background: #17141a;
    color: #fff7e6;
  }
  100% {
    background: #fff7e6;
    color: #17141a;
  }
}
@keyframes ripple-wave {
  0% {
    box-shadow: 0 0 0 0 rgba(47, 109, 246, 0.48), 0 0 0 0 rgba(47, 109, 246, 0.28);
    opacity: 1;
  }
  38% {
    box-shadow: 0 0 0 10px rgba(47, 109, 246, 0.2), 0 0 0 4px rgba(47, 109, 246, 0.26);
    opacity: 0.74;
  }
  66% {
    box-shadow: 0 0 0 17px rgba(47, 109, 246, 0.09), 0 0 0 11px rgba(47, 109, 246, 0.15);
    opacity: 0.36;
  }
  100% {
    box-shadow: 0 0 0 24px rgba(47, 109, 246, 0), 0 0 0 20px rgba(47, 109, 246, 0);
    opacity: 0;
  }
}
@keyframes ripple-loop {
  0%, 20% {
    box-shadow: 0 0 0 0 rgba(47, 109, 246, 0.48), 0 0 0 0 rgba(47, 109, 246, 0.28);
    opacity: 1;
  }
  38% {
    box-shadow: 0 0 0 10px rgba(47, 109, 246, 0.2), 0 0 0 4px rgba(47, 109, 246, 0.26);
    opacity: 0.74;
  }
  55% {
    box-shadow: 0 0 0 17px rgba(47, 109, 246, 0.09), 0 0 0 11px rgba(47, 109, 246, 0.15);
    opacity: 0.36;
  }
  75%, 100% {
    box-shadow: 0 0 0 24px rgba(47, 109, 246, 0), 0 0 0 20px 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;
  }
}

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

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

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

/** @media (hover: none) and (pointer: coarse) 에서만 :active 배경이 걸린다. 마우스 기기에서는 이 규칙이 아예 읽히지 않는다. */
export default function TouchActiveButton({
  label,
  duration = 220,
  easing = "ease-out",
  color = "#fff7e6",
}: TouchActiveButtonProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  return (
    <button type="button" className={styles.btn} style={vars}>
      {label}
    </button>
  );
}