Customizing a few things on the WP login form

Hello,
Login URL: http://yourtechadvisors.com/wp-admin
I would like to do the following to the login form.
1. Change the login button background to black and login text white.
2. Center the logo above the login message.
I already have a customization plugin installed, so all I need is the css code to put in the plugin.

Support access is open.

Thanks.