top-bar position when sticky

fixed a problem when the top-bar is sticky that it will have its fixed position removed when clicking the menu icon and it will disappear from view until the user scrolls again. 

also corrected the offset calculation for its home position when resizing the window. currently the t_top var is not declared and needed to be, and the new offset that was being obtained was calculated from the fixed position not from the home position of the top-bar.