Custom CSS not working

Hi @decio,
on the official site http://www.simplestgallery.com you can see that the custom CSS feature is working.
Open http://www.simplestgallery.com then view the page source (CTRL-U or Command-U) and you can locate this code:

<style type="text/css">
.customclass {
color:#aabbcc;
}
</style>

this has been entered in the Custom CSS field in the settings.

Therefore, by using the same procdeure on your site you should see your custom CSS code. If not, then the problem is likely that the class or id specifier in your CSS code is wrong.
But if the custom CSS code cannot be found on your site, then yes, surely there’s something that is not working.

Please, post a link to your site and paste your custom code so that I can check and verify.