모달 팝업 (Modal Popup)
완전 정복 가이드

<!-- HTML 구조 -->
<button onclick="openModal()">모달 열기</button>

<div class="modal-overlay" id="myModal"
     onclick="handleOverlayClick(event)">
  <div class="modal-box">
    <button class="modal-close" onclick="closeModal()">✕</button>
    <h2>모달 제목</h2>
    <p>모달 내용이 여기에 들어가요.</p>
    <button onclick="closeModal()">확인</button>
  </div>
</div>

/* CSS 스타일 */
.modal-overlay {
  position: fixed;
  inset: 0;                         /* top:0; right:0; bottom:0; left:0 */
  z-index: 1000;
  background: rgba(0, 0, 0, 0.55);
  backdrop-filter: blur(4px);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 24px;
  opacity: 0;
  visibility: hidden;
  transition: opacity .22s ease, visibility .22s ease;
}
.modal-overlay.open {
  opacity: 1;
  visibility: visible;
}
.modal-box {
  background: #fff;
  border-radius: 16px;
  box-shadow: 0 24px 64px rgba(0,0,0,.18);
  width: 100%;
  max-width: 440px;
  padding: 32px;
  position: relative;
  transform: translateY(16px) scale(.97);
  transition: transform .25s cubic-bezier(.34,1.56,.64,1);
}
.modal-overlay.open .modal-box {
  transform: translateY(0) scale(1);
}
.modal-close {
  position: absolute;
  top: 16px; right: 16px;
  background: #f3f4f6;
  border: none;
  border-radius: 50%;
  width: 30px; height: 30px;
  cursor: pointer;
}

// JavaScript
function openModal() {
  document.getElementById('myModal').classList.add('open');
  document.body.style.overflow = 'hidden';  // 배경 스크롤 막기
}

function closeModal() {
  document.getElementById('myModal').classList.remove('open');
  document.body.style.overflow = '';         // 스크롤 복구
}

function handleOverlayClick(e) {
  if (e.target === e.currentTarget) closeModal(); // 오버레이만 클릭 시
}

// ESC 키로 닫기
document.addEventListener('keydown', (e) => {
  if (e.key === 'Escape') closeModal();
});