Menu with slider

Hello, everyone!

I’m new to this forum, to AS and everything. I have a short question:

I made menu with slider like in tutorial on kirupa.com and everything is ok. But how to change the width of the slider if the buttons don’t have the same size? I know how to do it, but how to do it animated. Example: button1 is 150px wide (and slider also), button2 is 110 px wide - how to make slider (when sliding from button1 to button2) smaller (animated).

Thanks.