I tried to validate the css of index,and I got a million errors,all about "opacity".
Since W3C gives you the "purged"css I copied it and replaced it on the ftp.
I strongly recommend textwrangler, it's free and you can fix a lot of stuff right at your server.
I used it to get rid of underline text-decorations, fix bad links, and edit any file already uploaded.
I uploaded the css tey gave me and i am css validated and also html. With wrangler I put the W3C icons. Check it out:
http://ionmuniz.mus.br/

W3C validating an iWeb css has to be "purged" of the following items:

************
body {
-webkit-text-size-adjust: none;
}

***********

li.full-width {
width: 100;
}
*************

opacity: 1.00;

after validating you can sport the little button ...
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Before uploading hte site get Mass Replace it, choose the whole folder and change the 3 items above for nothing.