Y positioning noob question

Hi,

I have a bottom bar on a site that has he following code:

nav_menu.menu_bars._y = 0;

But I want it to be at the top of the stage. Sorry for such a noob question, but how do it?

I’ve tried nav_menu.menu_bars._y = -600;

but when the browser is resized it obviously moves down the page.

Is there a bit of code to keep it at top of the stage?

Thanks in advance, sorry for the noob question!