How to add custom CSS to the WordPress admin area

This snippet will change the default style of WordPress admin area by overriding the old stylesheet (CSS).

Instructions
1) Create a new css file in your theme folder, and then include it in WP-Admin using the admin_head hook.
2) Add this to your functions.php file.

* Change the paths according to where you put your new/extra wp-admin.css file.
* Add whatever styles you want to override the defaults with, or copy the old stylesheet and use as a template for your new one. Location: /wp-admin/css/colors-fresh.css.