css style switching

I'm trying to use a radio box button to switch between two style sheets for a page:

In index.php

Code:

---

<input type="radio" name="css" value="style.css"/> Web
<input type="radio" name="css" value="print.css"/> Print
<input type="submit" value="Switch styles"/>

---

new pages get loaded in my <div class=main> using a switch/case structure that uses include.

So every page loaded in the main <div> may be displayed using either the style.css or the print.css, changeable with the radio buttons.

However, it doesn't work. What am I doing wrong?

Thanks in advance.