Better fill colors for Facebook and GitHub links in the footer

**Is your feature request related to a problem? Please describe.**
The icon link for GitHub at the footer has very poor contrast and therefore is hard to read.

**Describe the solution you'd like**
I would like to change these default and hover colors for the GitHub icon to `#ccc` and `white` respectively. Inspired by the following site: https://dunks1980.com/


This will result in better readability and contrast.

While I'm at it, I would also like to change the default color of the Facebook icon to match with the GitHub icon. And also change the hover fill color to the appropriate official Facebook primary color on their website:


**Proposed result*
Default state:

Hover state:

As you can see this will result in better readability and consistency between the two icons.