3
Okey, seems like the order of css inclusion does make difference. My fault.
Edit modules/system/themes/default/default.php and change
$xoTheme->addStylesheet(XOOPS_ADMINTHEME_URL . '/default/css/dark.css', array('title' => 'dark', 'media' => 'screen'));
$xoTheme->addStylesheet(XOOPS_ADMINTHEME_URL . '/default/css/silver.css', array('title' => 'silver', 'media' => 'screen'));
$xoTheme->addStylesheet(XOOPS_ADMINTHEME_URL . '/default/css/orange.css', array('title' => 'orange', 'media' => 'screen'));
$xoTheme->addStylesheet(XOOPS_ADMINTHEME_URL . '/default/css/style.css' );
Into
$xoTheme->addStylesheet(XOOPS_ADMINTHEME_URL . '/default/css/style.css' );
$xoTheme->addStylesheet(XOOPS_ADMINTHEME_URL . '/default/css/dark.css', array('title' => 'dark', 'media' => 'screen'));
$xoTheme->addStylesheet(XOOPS_ADMINTHEME_URL . '/default/css/silver.css', array('title' => 'silver', 'media' => 'screen'));
$xoTheme->addStylesheet(XOOPS_ADMINTHEME_URL . '/default/css/orange.css', array('title' => 'orange', 'media' => 'screen'));