Works for us
The change would be in the /modules/mod_sclogin.php file. Around line 90, you'll see:
$paths = array();
$paths[] = JPATH_ROOT . '/templates/' . JFactory::getApplication()->getTemplate() . '/html/mod_sclogin/themes/';
$paths[] = JPATH_ROOT . '/media/sourcecoast/themes/sclogin/';
Those are the 2 paths that the SCLogin module will look in for the theme CSS files.
That location will likely change in the next major release as that mod_sclogin.php file is way to big and cumbersome right now.. either way, that should get you going for now!
Should you need anything else, just let me know.
Thanks,
Alex