After some Googling I found several interesting articles, most of them repeated themselves and said “well.. edit the ksas.php file in wp-includes” and then stated a long-list with many interesting HTML pieces. This works, but a plugin is more fancy I thought: so I googled on and found a plugin called “unfiltered” content WordPress MU, released by the WordPress guys. This is in so far cool, as you can either stick it in the mu-plugins folder and have it sidewide, or in the regular plugins folder and just activate it on a blog by blog basis. Since I am running this WordPress MU installation on my own and do not have posts to monitor for “havoc causing script includes”, I decided to go for the plugin and enable it side-wide. This way I can upgrade my wordpress mu next time a new version comes out and keep my sanity (because by then I would probably have forgotten about the includes folder and the php file that I need to update every time…)

Hope this helps,
best,
jez

Here is the old css (excerpt)

input { border: 1px solid rgb(204, 204, 204); padding: 3px 6px; background: rgb(255, 255, 255) none repeat; color: rgb(102, 102, 102); }

and here a quick screencap of what the problem looked like:

I applied this quick CSS hack to my code to make the border disappear:

input[type="hidden"] { border: 0; padding: 0; margin: 0; background: white; }

(marked green in screencap)

Voila, the rectangles are gone. No more annoying borders around hidden input fields with CSS.

I hope this helped anyone. You can do a similar trick with the input property “submit” if you want to apply different CSS attributes to your input submit form only.