03Nút bị hút như nam châm

<main class="stage">
  <button class="btn is-demo" type="button">Bắt đầu</button>
  <div class="cursor is-demo" aria-hidden="true"></div>
</main>

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

$duration: $dur-loop;                                // 커서가 버튼을 스치는 한 바퀴
$easing: $ease-spring;
$color: $subject-cream;                               // 버튼 색

@include stage($stage-orange);

.stage { position: relative; overflow: hidden; cursor: none; }

.btn {
  position: relative;
  border: 0;
  border-radius: $r-pill;
  padding: clamp(12px, 3.4vw, 18px) clamp(26px, 7vw, 40px);
  font-weight: 700; font-size: clamp(14px, 3.8vw, 18px); line-height: 1; font-family: inherit;
  color: $subject-orange-deep;                          // AA: 크림 면 위 주황 글자 5.04:1
  background: $color;
  cursor: pointer;
  transition: transform 160ms $easing;                 // 실제 조작에서 버튼이 끌려가는 부드러움

  &.is-demo { animation: magnet-pull $duration $easing infinite; }
}

.cursor {
  position: absolute;
  top: 0;
  left: 0;
  width: 14px;
  height: 14px;
  margin: -7px 0 0 -7px;
  border-radius: 50%;
  background: $stage-ink;
  pointer-events: none;

  &.is-demo { animation: cursor-path $duration $easing infinite; }
}

@keyframes magnet-pull {
  0%, 100% { transform: translate(0, 0); }
  35%      { transform: translate(12px, -8px); }
  55%      { transform: translate(0, 0); }
}

@keyframes cursor-path {
  0%   { transform: translate(30px, 150px); }
  35%  { transform: translate(150px, 60px); }          // 버튼 근처를 스친다
  70%  { transform: translate(280px, 190px); }
  100% { transform: translate(30px, 150px); }
}

@media (pointer: coarse) {
  .cursor { display: none; }
  .stage { cursor: auto; }
}

@media (prefers-reduced-motion: reduce) {
  .btn.is-demo { animation: none; }
  .cursor.is-demo { animation: none; transform: translate(30px, 150px); }
  .btn { transition: 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);
}

.stage {
  position: relative;
  overflow: hidden;
  cursor: none;
}

.btn {
  position: relative;
  border: 0;
  border-radius: 999px;
  padding: clamp(12px, 3.4vw, 18px) clamp(26px, 7vw, 40px);
  font-weight: 700;
  font-size: clamp(14px, 3.8vw, 18px);
  line-height: 1;
  font-family: inherit;
  color: #c93000;
  background: #fff7e6;
  cursor: pointer;
  transition: transform 160ms cubic-bezier(0.2, 0.8, 0.2, 1);
}
.btn.is-demo {
  animation: magnet-pull 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

.cursor {
  position: absolute;
  top: 0;
  left: 0;
  width: 14px;
  height: 14px;
  margin: -7px 0 0 -7px;
  border-radius: 50%;
  background: #17141a;
  pointer-events: none;
}
.cursor.is-demo {
  animation: cursor-path 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@keyframes magnet-pull {
  0%, 100% {
    transform: translate(0, 0);
  }
  35% {
    transform: translate(12px, -8px);
  }
  55% {
    transform: translate(0, 0);
  }
}
@keyframes cursor-path {
  0% {
    transform: translate(30px, 150px);
  }
  35% {
    transform: translate(150px, 60px);
  }
  70% {
    transform: translate(280px, 190px);
  }
  100% {
    transform: translate(30px, 150px);
  }
}
@media (pointer: coarse) {
  .cursor {
    display: none;
  }
  .stage {
    cursor: auto;
  }
}
@media (prefers-reduced-motion: reduce) {
  .btn.is-demo {
    animation: none;
  }
  .cursor.is-demo {
    animation: none;
    transform: translate(30px, 150px);
  }
  .btn {
    transition: none;
  }
}

// 실제 포인터가 버튼 반경 90px 안에 들어오면 거리에 비례해 버튼이 그쪽으로 끌려간다.
if (matchMedia('(pointer: fine)').matches) {
  var stage = document.querySelector('.stage'), btn = document.querySelector('.btn'), cur = document.querySelector('.cursor');
  stage.addEventListener('pointermove', function (e) {
    cur.classList.remove('is-demo'); btn.classList.remove('is-demo');
    var r = stage.getBoundingClientRect(), x = e.clientX - r.left, y = e.clientY - r.top;
    cur.style.transform = 'translate(' + x + 'px,' + y + 'px)';
    var br = btn.getBoundingClientRect(), cx = br.left - r.left + br.width / 2, cy = br.top - r.top + br.height / 2;
    var dx = x - cx, dy = y - cy, dist = Math.hypot(dx, dy), pull = dist < 90 ? (90 - dist) / 90 : 0;
    btn.style.transform = 'translate(' + (dx * pull * .35) + 'px,' + (dy * pull * .35) + 'px)';
  });
}

import { useRef, useState } from "react";
import type { CSSProperties, PointerEvent } from "react";
import styles from "./MagneticCursorButton.module.scss";

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

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

export default function MagneticCursorButton({
  label = "시작하기",
  radius = 90,
  duration = 2000,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#fff7e6",
}: MagneticCursorButtonProps) {
  const btnRef = useRef<HTMLButtonElement>(null);
  const [demo, setDemo] = useState(true);
  const [cur, setCur] = useState({ x: 30, y: 150 });
  const [pull, setPull] = useState({ x: 0, y: 0 });

  const move = (e: PointerEvent<HTMLDivElement>) => {
    const r = e.currentTarget.getBoundingClientRect();
    setDemo(false);
    const x = e.clientX - r.left, y = e.clientY - r.top;
    setCur({ x, y });
    const br = btnRef.current!.getBoundingClientRect();
    const cx = br.left - r.left + br.width / 2, cy = br.top - r.top + br.height / 2;
    const dx = x - cx, dy = y - cy, dist = Math.hypot(dx, dy), p = dist < radius ? (radius - dist) / radius : 0;
    setPull({ x: dx * p * 0.35, y: dy * p * 0.35 });
  };

  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  return (
    <div className={styles.stage} style={vars} onPointerMove={move}>
      <button
        ref={btnRef}
        type="button"
        className={demo ? `${styles.btn} ${styles.isDemo}` : styles.btn}
        style={demo ? undefined : { transform: `translate(${pull.x}px,${pull.y}px)` }}
      >
        {label}
      </button>
      <div
        className={demo ? `${styles.cursor} ${styles.isDemo}` : styles.cursor}
        style={demo ? undefined : { transform: `translate(${cur.x}px,${cur.y}px)` }}
        aria-hidden="true"
      />
    </div>
  );
}