#box1{
      box-sizing: border-box;
      height: 100px;
      width: 100px;
      border: 20px solid gray;
      background-color:bisque;
      padding: 100px;
      margin: 50px;
    }

    元素的实际高度 = 240px  = max(padding + border, height) 

    #box2{
      box-sizing: content-box;
      height: 100px;
      width: 100px;
      border: 20px solid gray;
      background-color:bisque;
      padding: 100px;
      margin: 50px;
    }
    元素的实际高度 = 340px = height + padding + border