01Ring pulse (outline, not fill)

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

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

// ── 변수 3개. 변형은 이것만 바꾼다 ──────────────────────────
$duration: $dur-enter;                            // 링이 다 부풀고 사라지는 시간
$easing: $ease-out;
$color: $subject-blue;                            // 버튼·링 색

@include stage($stage-ink);

.btn {
  position: relative;
  border: 0;
  border-radius: $r-pill;
  padding: 18px 40px;
  font-weight: 600; font-size: 18px; line-height: 1; font-family: inherit;
  color: $subject-cream;
  background: $subject-blue-deep;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  transition: filter $dur-quick;

  &:hover { filter: brightness(1.06); }
  &:active { filter: brightness(.96); }

  // 채워지는 원(::after 가 버튼 내부를 덮는 리플)이 아니라, 버튼 바깥으로 테두리만 번지는 링
  // 규칙8 한 겹: 링 하나가 아니라 두 겹이 서로 다른 속도로 번져 노이즈처럼 불규칙한 파면을 만들고,
  // 바깥 겹이 안쪽 겹보다 먼저 옅어지며 감쇠한다(선형 감쇠가 아니라 24%→52%→78% 단계별로 빠르게 줄어듦)
  &::after {
    content: "";
    position: absolute;
    inset: -2px;
    border-radius: inherit;
    box-shadow: 0 0 0 0 rgba($color, .55), 0 0 0 0 rgba($color, .32);
    opacity: 0;
    pointer-events: none;
  }

  &.is-ringing::after {
    animation: ring $duration $easing forwards;
  }

  // 데모용: 클릭 여부와 무관하게 2초마다 자동 반복. linear 로 프레임마다 고르게 퍼지게 한다
  &.is-demo::after {
    animation: ring-loop $dur-loop linear infinite;
  }
}

@keyframes ring {
  0%   { box-shadow: 0 0 0 0 rgba($color, .68), 0 0 0 0 rgba($color, .44); opacity: 1; }
  30%  { box-shadow: 0 0 0 8px rgba($color, .4), 0 0 0 3px rgba($color, .44); opacity: 1; }
  62%  { box-shadow: 0 0 0 14px rgba($color, .18), 0 0 0 9px rgba($color, .24); opacity: .72; }
  86%  { box-shadow: 0 0 0 17px rgba($color, .04), 0 0 0 12px rgba($color, .06); opacity: .16; }
  100% { box-shadow: 0 0 0 17px rgba($color, 0), 0 0 0 12px rgba($color, 0); opacity: 0; }
}

@keyframes ring-loop {
  0%, 8%  { box-shadow: 0 0 0 0 rgba($color, .68), 0 0 0 0 rgba($color, .44); opacity: 1; }
  24%     { box-shadow: 0 0 0 8px rgba($color, .4), 0 0 0 3px rgba($color, .44); opacity: 1; }
  40%     { box-shadow: 0 0 0 14px rgba($color, .18), 0 0 0 9px rgba($color, .24); opacity: .72; }
  52%     { box-shadow: 0 0 0 17px rgba($color, .04), 0 0 0 12px rgba($color, .06); opacity: .16; }
  62%, 100% { box-shadow: 0 0 0 17px rgba($color, 0), 0 0 0 12px rgba($color, 0); opacity: 0; }
}

@media (prefers-reduced-motion: reduce) {
  .btn::after { animation: none !important; opacity: 0; }
  .btn:active { filter: brightness(.88); }
}

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 {
  position: relative;
  border: 0;
  border-radius: 999px;
  padding: 18px 40px;
  font-weight: 600;
  font-size: 18px;
  line-height: 1;
  font-family: inherit;
  color: #fff7e6;
  background: #0a4fe8;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  transition: filter 220ms;
}
.btn:hover {
  filter: brightness(1.06);
}
.btn:active {
  filter: brightness(0.96);
}
.btn::after {
  content: "";
  position: absolute;
  inset: -2px;
  border-radius: inherit;
  box-shadow: 0 0 0 0 rgba(47, 109, 246, 0.55), 0 0 0 0 rgba(47, 109, 246, 0.32);
  opacity: 0;
  pointer-events: none;
}
.btn.is-ringing::after {
  animation: ring 600ms ease-out forwards;
}
.btn.is-demo::after {
  animation: ring-loop 2s linear infinite;
}

@keyframes ring {
  0% {
    box-shadow: 0 0 0 0 rgba(47, 109, 246, 0.68), 0 0 0 0 rgba(47, 109, 246, 0.44);
    opacity: 1;
  }
  30% {
    box-shadow: 0 0 0 8px rgba(47, 109, 246, 0.4), 0 0 0 3px rgba(47, 109, 246, 0.44);
    opacity: 1;
  }
  62% {
    box-shadow: 0 0 0 14px rgba(47, 109, 246, 0.18), 0 0 0 9px rgba(47, 109, 246, 0.24);
    opacity: 0.72;
  }
  86% {
    box-shadow: 0 0 0 17px rgba(47, 109, 246, 0.04), 0 0 0 12px rgba(47, 109, 246, 0.06);
    opacity: 0.16;
  }
  100% {
    box-shadow: 0 0 0 17px rgba(47, 109, 246, 0), 0 0 0 12px rgba(47, 109, 246, 0);
    opacity: 0;
  }
}
@keyframes ring-loop {
  0%, 8% {
    box-shadow: 0 0 0 0 rgba(47, 109, 246, 0.68), 0 0 0 0 rgba(47, 109, 246, 0.44);
    opacity: 1;
  }
  24% {
    box-shadow: 0 0 0 8px rgba(47, 109, 246, 0.4), 0 0 0 3px rgba(47, 109, 246, 0.44);
    opacity: 1;
  }
  40% {
    box-shadow: 0 0 0 14px rgba(47, 109, 246, 0.18), 0 0 0 9px rgba(47, 109, 246, 0.24);
    opacity: 0.72;
  }
  52% {
    box-shadow: 0 0 0 17px rgba(47, 109, 246, 0.04), 0 0 0 12px rgba(47, 109, 246, 0.06);
    opacity: 0.16;
  }
  62%, 100% {
    box-shadow: 0 0 0 17px rgba(47, 109, 246, 0), 0 0 0 12px rgba(47, 109, 246, 0);
    opacity: 0;
  }
}
@media (prefers-reduced-motion: reduce) {
  .btn::after {
    animation: none !important;
    opacity: 0;
  }
  .btn:active {
    filter: brightness(0.88);
  }
}

// 링은 클릭이 끝나도 끝까지 재생돼야 해서 :active 만으로는 부족하다. pointerdown 에서 클래스를 한 번 갈아끼운다.
var b = document.querySelector('.btn');
b.addEventListener('pointerdown', function () {
  b.classList.remove('is-demo');
  b.classList.remove('is-ringing');
  void b.offsetWidth;
  b.classList.add('is-ringing');
});
b.addEventListener('animationend', function (e) {
  if (e.animationName === 'ring') b.classList.remove('is-ringing');
});

import { useCallback, useRef, type CSSProperties } from "react";
import styles from "./RingPulseButton.module.scss";

export type RingPulseButtonProps = {
  label: string;
  /** 링이 다 부풀고 사라지는 시간 (기본 600ms) */
  duration?: number;
  easing?: string;
  /** 버튼·링 색 */
  color?: string;
};

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

export default function RingPulseButton({
  label,
  duration = 600,
  easing = "ease-out",
  color = "#0a4fe8",
}: RingPulseButtonProps) {
  const ref = useRef<HTMLButtonElement>(null);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  // 클릭이 끝나도 링은 끝까지 재생돼야 해서 :active 만으로는 부족하다 (index.html 과 같은 이유)
  const onPointerDown = useCallback(() => {
    const b = ref.current;
    if (!b) return;
    b.classList.remove(styles.ringing);
    void b.offsetWidth;
    b.classList.add(styles.ringing);
  }, []);

  const onAnimationEnd = useCallback((e: { animationName: string }) => {
    if (e.animationName.includes("ring")) ref.current?.classList.remove(styles.ringing);
  }, []);

  return (
    <button
      ref={ref}
      type="button"
      className={styles.btn}
      style={vars}
      onPointerDown={onPointerDown}
      onAnimationEnd={onAnimationEnd}
    >
      {label}
    </button>
  );
}