[css] How would you make two <div>s overlap?

If you want the logo to take space, you are probably better of floating it left and then moving down the content using margin, sort of like this:

#logo {
    float: left;
    margin: 0 10px 10px 20px;
}

#content {
    margin: 10px 0 0 10px;
}

or whatever margin you want.