How to move first element if second is over it : Sorry for my bad english :)

1) Sidebar moves to the right (Start Left position = -270, End position = 0);

2) Header contains logo <div class="head-logo"></div> with position:absolute

How to to move logo div to left if sidebar above the logo?

[What I need][1]


  [1]: http://i.stack.imgur.com/t0rJl.png