As I mentioned in an earlier thread of yours, the nav buttons change position because of inconsistency of coding within the different pages of your website.
On some after <BODY> tag line, <CENTER> appears which causes the whole page to be centred, including nav buttons, all except the green column. The visual effect is NAV buttons misaligned with the background. On pages where <CENTER> is not present, whole page is automatically aligned left and nav buttons are within the green column.
Whichever style you prefer, if ALL pages have either <CENTER> tag OR no <CENTER> tag, the nav buttons will not move, whatever screen you put them on.