make li beautiful and in the middle of the page

.todo-list li {
    margin: 15px 0;
    padding: 15px 15px;
    font-size: 24px;
    color: #333;
    border: 1px solid grey;
    border-radius: 3px;
    text-align: center;
    width: 500px;
    height: 200px;
  }