wordpress login page

I was wondering if anyone could help point me in the right direction, I have searched and searched the internet and could not really find the answer i have been looking for….

I have customized my login page with my logo, the colors i want the width of box ect, my problem is, that everytime wordpress updates to a newer version all my customization is lost, and it takes me a good 2 hrs to re customize it…

Is their anyway that i can create a login page that does not touch the core files so when i update wordpress its not effected.

I dont want to use theme my login plugin, i basically want to take the code in wp-login.php and create a login page with that code and just add my customizations to it…

i thought it would be easy, but it appears not to be so easy, i was having the same issue with my theme everytime the developer updated it i would loose my customization until i learned how how to create a child theme….

i didnt know if their maybe some kind of tutorial out their or video tutorial to show how to accomplish this..

The only kind of tutorial i have found is how to create a login page from createing a wordpress page so the form would appear on a page and thats not what i want to do..

Thanks in advance any help is appreciated.