如何在一个页面上创建以NxM为中心的大按钮？

<div id="button-container"></div>

#button-container {
  display: flex;
  justify-content: center;
  align-items: center;
  width: 300px; /* 根据需求设置容器宽度 */
  height: 200px; /* 根据需求设置容器高度 */
  border: 1px solid #000; /* 可选，添加边框效果 */
}

var buttonContainer = document.getElementById("button-container");

for (var i = 0; i < N; i++) {
  for (var j = 0; j < M; j++) {
    var button = document.createElement("button");
    button.id = "button-" + i + "-" + j;
    button.innerHTML = "Button " + i + "-" + j;
    buttonContainer.appendChild(button);
  }
}