I’ve seen that page, yes. I’m wondering if there is an issue with placing the conditional within CSS code, or if it’s only used within HTML code or to link to external stylesheets.
slight nitpicking: conditional comments are not only for linking to external style sheet, you can also put a few CSS declarations in there. But yes, it’s meant to be in the HTML header, not in the CSS
Reason it works that way is because IE’s conditionals are in HTML comments that are incorrect syntax for a CSS parser so just returns an error (browser ignores it). It’s always easier to just have an external stylesheet, and most of the time there’s more than one fix needed