参考:https://blog.youkuaiyun.com/zwkkkk1/article/details/79678177
box-sizing: content-box
盒子width = content的width
box-sizing: border-box 盒子width = (content+border)的width
参考:https://blog.youkuaiyun.com/zwkkkk1/article/details/79678177
box-sizing: content-box
盒子width = content的width
box-sizing: border-box 盒子width = (content+border)的width