How do I resize a div/element that's position fixed with css ?

Supper,

I set up a fixed element using this code in stage/ composition ready :

sym.$("body").append(sym.$("Group").css({"position":"fixed"}));

The element does "position:fixed" but its size has changed.

How do I resize it to its previous size?

I tried the same css insertion method with size properties as I used in "fixed"( example above) .

It Failed.

So second question is based on that it also loses its "responsive scaling" properties

(just the "fixed" element not the rest of the project)

and no longer zooms in scale.

Can I fix an elements position and maintain scaling with the rest of the project at 100% width?

My objective is to scroll under a fixed element scaled to fit browser.

Thank You,

Henry