Beginnings of a built in - the sides

I've built two base cabinets for either side of the window.  These are 24" deep and will have bookshelf sections above.  I've also assembled the tops for these, and trimmed them out underneath.  There will be a window seat between the two side towers.  I've used basic cabinets construction and pocket hole joinery for the tops - see previous posts on how to do this.