ok, I see there is code that simply loads all css files inside the css directory of the current template, is this piece of code
PHP Code:
    foreach($files['css'] as $file)
        if(
$file['include']) include($file['src']);
        else if(!
$RI_CJLoader->get('minify') || $file['external']) echo "<link rel=\"stylesheet\" type=\"text/css\" href='{$file['src']}' />\n";
        else echo 
"<link rel=\"stylesheet\" type=\"text/css\" href=\"min/?f={$file['src']}&amp;".$RI_CJLoader->get('minify_time')."\" />\n"
This is part of the minify script, but it does load all css files inside the directory. So now I understand why there is nothing to be added just the file and it will be loaded automatically by the code.