<button onclick="showModal()">點擊我彈出框</button>

function showModal() {
// 獲取彈出框的容器
var modal = document.getElementById("myModal");
// 設置彈出框的樣式和位置
modal.style.display = "block";
modal.style.position = "fixed";
modal.style.top = "50%";
modal.style.left = "50%";
modal.style.transform = "translate(-50%, -50%)";
}

<div id="myModal" class="modal"><div class="modal-content"><span class="close">×<!-- 在彈出框中添加需要顯示的內容 --></div></div>

var closeButton = document.getElementsByClassName("close")[0];
closeButton.onclick = function() {
// 獲取彈出框的容器
var modal = document.getElementById("myModal");
// 關閉彈出框
modal.style.display = "none";
}