pt_side_pagetabs and side menu. Not sliding away as the page width gets smaller

Hi Folks,

when you do an activity guide, and you get the menu at the side, when you reduce the width of the page the side menu slides out of the way to make more room for the main page.

However, when you put the fluid ps_side_pagetabs page onto the end of your component, you also get the side menu, but it doesn't automatically slide away as the page width reduces.

There must be some css magic that I'm missing.

Thanks in advance,

Ian.