Shoutbox

No, it is in no way at all possible to hide the CSS from the user.  If the browser have to reach it, the user will be able as well.  These things are client sided, and thus all information send by the server can be used by the browser.

Another reason is that the feature you are asking for is not standardized javascript, and is only supported by Microsoft's Internet Explorer browsers.  Users using other browsers will not at all feel the affect, in fact, extentions in Mozilla's Firefox enables the user to actually get the CSS by clicking a button.

So no, you cannot hide the CSS, and why would you?  Does he steal it?  Who cares?  He is probably a noob and knows nothing.

Besides and for the record, CSS, HTML, PHP and MySQL are no where similar to each other, they are four completely different things.  Although they are normally used together to form websites (such as this), but one of them does not require the other (although CSS would look stupid without HTML, and PHP works best when outputting HTML (but can be used for other stuff as well)).