css div水平垂直居中

< STYLE TYPE ="text/css" > ...
.middle-demo-4{...}{
height:400;
width:100%;
position:relative;

background:#aaa;
}
.middle-demo-4div{...}{
position:absolute;
top:50%;
left:50%;
background:blue
}
.middle-demo-4divdiv{...}{
position:relative;
top:-50%;
left:-50%;
background:yellow;
overflow:hidden;

}
</ STYLE >

< div class =middle-demo-4 >
< div >
< div > helpipsumdolorsitamet,consectetueradipiscingelit.asdsadfs. < br >< img src =1.jpg width =140 height =100 > asdsadfs. < br > asdsadfs.asdsadfs. < br > asdsadfs.asdsadfs. </ div >
</ div >
</ div >