I recently ran across this positioning problem. I was setting up a site where I needed a div layer (nav element) to go inside a layer with 100% width. I needed to position the div absolute, top and also align it in the middle of the page (see Pasta Technology for demo). CSS doesn’t always behave like you expect it would. But in the event you were wondering how to align your div top and center, here is the solution.

Set your container element’s position as absolute with top as 0px, if necessary. Next give it a position of left: 50%. Give the div an appropriate width for its contents. Then set it up with a margin-left as the negative value of half of the width. See my example:

#headerInside {
       position:     absolute;
       top:          0px;
       left:         50%;/*some magic to align the element in the center;
       width:        1000px;
       margin-left:  -500px;/* half of the width */
}

You can also use the same principle if you want to align the element in the middle of the page vertically, by using top: 50%.