The reason this happens is because you are missing a <body>
open tag. When the <body>
open tag is not explicitly in the HTML, IE (6 at least ) misrenders the document tree and any selectors involving form
elements don't work properly.
Here, I added the body tag and it works.
Just yesterday I documented pretty much the same bug. It looks like I'll have to update the description to account for not only the form being unstylable with the body tag missing, but other elements unstylable if its in the selector.
And as doctororange points out, you can workaround this by not specifying form
in the selector as well, but I advise you to throw in the <body>
tag.