I've just tested it with the mypage module as outlined in the XOOPS faq, and it does work so now we just need to work out why it's not working for you ...
In the code I pasted there were two parts that you needed to change to match your setup.
The first is the name of your css file. You should have made a css file, called it whatever you want, and put that name at the end of the code I pasted, replacing the 'mypage.css' with the actual name of your css file.
I made a quick css file just for testing, which I called mypage.css. This file is in the same folder that the index.php file is, for this module. It looks like this:
body {
background-color: #009999;
}
That just gives the background a green colour, to show it's using this css file.
To make my code work you need to add the correct url for this file. If you changed the name of the mypage module folder, you need to use that name in the url. Same with the css file, you need to use the right name. The url is in the last part of the code snippet:
XOOPS_URL . "/modules/mypage/mypage.css'/>");
If you make sure the module name is right, and css file name is right, it should work exactly as I posted previously
So your index.php file for your mypage module should look like this (with the module name changed to your module name, and the css file name changed to your css file).
include("../../mainfile.php");
include(XOOPS_ROOT_PATH."/header.php");
$xoopsOption['show_rblock'] = 1;
$xoopsTpl->assign("xoops_module_header", ". XOOPS_URL . "/modules/[color=00CC33]yourMypageHere[/color]/[color=CC0000]YourCSSFileHere.css[/color]'/>");
?>
Let me know how you go...
Rowd