Text resizing

ok, this one has had me stumped all day.

I have a dynamic textfield into which I load text from the first node in an xml doc. 2 buttons (previous and next) are used to go through the nodes - so far so good. My client has now requested that the text be resizable using 2 buttons ( a small ‘A’ and a larger ‘A’). I guess this would involve applying a stylesheet initially and then having the 2 buttons dynamically switch between 2 classes in the stylesheet (one for small text and one for large text). Ideally I’d like the timeline to stay on the same frame throughout. Files attached.

Anyone have any ideas? Help much appreciated.