The best part is that this time you are allowed to edit "core" files, alter all installation directory with your beautifull design will be deleted afret installation is completed. First go to your installation folder and find template folder.
You edit index.php and your css.In this file you find:
$doc = JFactory::getDocument();
then you need to include your custom css file which is located inside css folder:
Next step is to include your custom logo, some graphics etc.
You have to apply your own classes and style it to fit your needs.
For the purpose of this article I have used gantry's installer which was created by Rockettheme, which I have slightly modified to fit my purpose. I would like to give them credit for another great work! The final result is below.
I hope you find this articles helpfull. Thank you for reading.