CSS 保证金属性简化
示例
p {
margin:1px; /* 1px margin in all directions */
/*equals to:*/
margin:1px 1px;
/*equals to:*/
margin:1px 1px 1px;
/*equals to:*/
margin:1px 1px 1px 1px;
}另一个例子：
p{
margin:10px 15px; /* 10px margin-top & bottom And 15px margin-right & left*/
/*equals to:*/
margin:10px 15px 10px 15px;
/*equals to:*/
margin:10px 15px 10px;
/* margin left will be calculated from the margin right value (=15px) */
}