[CSS]exclude 1 style in 1 page

I've made a stylesheet for some 40 pages. All of them have the following properties from within the stylesheet:

html,body {
margin:0;
padding:0;
overflow:hidden;
}

One of these pages contains an iframe. This one should be scrollable but contains all of the other styledefenitions from the other pages. I could just make a copy of the first stylesheet and delete the overflow:hidden, but I don't want the extra work just in case I would want to change a lot of other styleproperties.

Is there a nice way to do this?

Just change it on the fly with: