I know how frustrating this is, - I did go through something similar. What I didn't know then that I do know now, is that when testing and you come upon an error, once you've tried stuff and reuploaded files etc, you must close the browser completely and then reopen it before going to your page to see if your modification was any good.
It might help you to have a look at my Spry .css files - the ones that I modified but work OK (and perhaps try substituting them for yours to see if that makes a difference), so I attach them here. You might get something from looking at the contactus.php page code too, so I include that.
But the WA Guys will be in tomorrow, and will probably have a fairly instant logical answer, so make sure to back up your files first if you should decide to try these 'known' working ones as I think they would want to see your originals. (You can see my heavily css-ified example form here. Feel free to send a message - the thank you page is styled similarly.
