Play cheat with W3C CSS Validator
If you design or create website you must validated the CSS and HTML. You can find the css and html validator from w3c validator. When i used thickbox in my site the css not valid cause thickbox used css3 and the validation use css level 2 
I think i must played cheat with this validation cause it’s make me feel sick. I make some modification for the engine for played cheat with this W3C engine.
First I learn what engine that W3C have and if found this on my engine [HTTP_USER_AGENT] => W3C_Validator/1.575 .When i see that i got the point, W3C used custom engine and the call the engine with W3C_Validator . I think i can modified my code and put some code for hide my thickbox.css from this engine.
This is the code for hide my CSS
<?php
$text = $_SERVER["HTTP_USER_AGENT"];
$findme = 'W3C';
$engine = strstr($email, $findme);
if (!preg_match("/".$findme."/i", $text)) { ?>
<link rel="stylesheet" href="thickbox.css" type="text/css" media="screen" />
<?php } ?>
You just need change the line 6 with your css that you want hide
And when i checked on W3C once more time, they said this site already validating 
you can see here
