How to center an iframe horizontally?

Question

Consider the following example: (live demo)

HTML:

div

CSS:

div         


        

Answer 1

HTML:

    
div
    

CSS:

#all{
    width:100%;
    float:left;
    text-align:center;
}
div.sub, iframe {
    width: 100px;
    height: 50px;
    margin: 0 auto;
    background-color: #777;

}