How to change the style sheet inside an .html file

A page has style sheet files. Any one might be active at a given time. They
all contain the same class names.

If on the page I have an iframe that loads a .html file I don't know how to
set the active style sheet in the .html to agree with the page it is on.

The usage of an iframe is not mandatory as long as I can inset the contents
of the .html into the page.

Even using .html is not mandatory but it is an easy way to obtain data to
display from people .

I thought I knew how but I was mistaken.


Any ideas?

Maybe a different approach to inserting formatted text?


Thanks