モーダル作成

<button id="modal-button">モーダル</button>

.modal {
  width: 100%;
  height: 100%;
  position: absolute;
  top: 0;
  left: 0;
  background-color: rgba(0, 0, 0, 0.2);
  display: flex;
  justify-content: center;
  align-items: center;
}

const modalButton = document.querySelector("#modal-button");
const setModal = () => {
  const modal = document.createElement("div");
  modal.classList.add("modal");
  modal.innerText = "色は匂へど";
  document.body.appendChild(modal);

  const closeModal = () => {
    modal.remove();
  }

  modal.addEventListener("click", closeModal);
}