The input type should not be 'yubikey', that would be an HTML error. Here are the tricks I've used for the demo server:
1) Auto-focus. Label the form, and use this:
2) Autocomplete off. Passwords are typically remembered by the browser, which we don't want. Add autocomplete=off to the input field.
I think there was a third item to keep in mind, but I can't recall it now...
Thus, the State of The Art Yubico-Compliant HTML input from page will look something like:
<input autocomplete="off" type="password" name="yubikey">
Of course, the auto-focus may not always be applicable. On the forum, I think it would interfere with the forum auto-focus design.
Hope this helps.