Describe the bug
The login button has a negative top-margin that can (depending on the logo size) obscure the custom logo. Additionally, (depending on the logo size) the logo may be left-aligned, when the expectation is for it to be centered.

To Reproduce
If you upload a logo that is 300 x 200, the bottom ~40px of the logo will be covered up by the login button. If you upload a logo that is smaller than 300px wide, the logo will align to the left of that 300px container.

Expected behavior
The expectation is for the custom logo to be centered and placed above the login button.

Screenshots

Applicable Versions:

• netlify-cms 2.5.1
• Git provider: GitHub
• OS: macOS 10.14.3
• Chrome Version 72.0.3626.119 (Official Build) (64-bit)
• Node.JS version: 11.10.0

CMS configuration
No can do, sorry.

Additional context
https://github.com/netlify/netlify-cms/blob/636a141a4ab3c4c9a490aea6956b32fec2324e08/packages/netlify-cms-ui-default/src/AuthenticationPage.js