CSS两种盒模型

1.content box

.content-box {
  margin: 25px;
  border: 5px solid red;
  padding: 15px;
  box-sizing: content-box;
  width:100px;
  height:100px;
}

content-box: 宽度只包含到content;
width=content

2.border box

.border-box {
  margin: 25px;
  border: 5px solid red;
  padding: 15px;
  box-sizing: border-box;
  width:100px;
  height:100px;
}

border box: 宽度包含到border;
width=content+padding+border