If I animate the
That's how fixed positioned elements work - they are positioned relative to the viewport.
See the CSS 2.1 specification:
Fixed positioning is a subcategory of absolute positioning. The only difference is that for a fixed positioned box, the containing block is established by the viewport. For continuous media, fixed boxes do not move when the document is scrolled. In this respect, they are similar to fixed background images.
You might animate
margin-left properties of the the fixed elements too.