CssHackie6,7,8的hack分别是什么

示例如下：

#test       {  
        width:300px;  
        height:300px;  
        background-color:blue;      /*firefox*/
        background-color:red\9;      /*all ie*/
        background-color:yellow;    /*ie8*/
        +background-color:pink;        /*ie7*/
        _background-color:orange;       /*ie6*/    } 
        :root #test { background-color:purple\9; }  /*ie9*/
    @media all and (min-width:0px){ #test {background-color:black;} }  /*opera*/
    @media screen and (-webkit-min-device-pixel-ratio:0){ #test {background-color:gray;} }       /*chrome and safari*/