盒子模型
*********************** border ***********************
* padding *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXX content XXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* *
********************************************************
margin
*********************** border ***********************
* padding *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXX content XXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX *
* *
********************************************************
盒子所在的实际宽度为:左右margin + 左右border + 左右padding + content
=============================================================================
padding 属性 (margin同)
(1)padding:a b c d; //上 右 下 左
(2)padding:x; //上=右=下=左
(3)padding:a b; //上=下 左=右
(4)padding:a b c; //上 右=左 下
**************按 上-->右-->下-->左 的顺序,没有赋值的等于其对面的值
====================================================================
由于各个浏览器存在着内外边距的默认值,且均不同,需要将所有浏览器默认的内外边距
都从零开始计算。
class,id,body{
padding:0;
margin:0;
}