[landing] reskin investors page

Summary:
This diff updates the UI (typography/colors) for the investors page. I worked closely with @ted on this, and made sure I got his stamp of approval

Depends on D8170

Test Plan:
Please see the demo videos/screenshots below:

Desktop/Responsive:

Tablet:

Mobile:

Reviewers: atul, kamil

Reviewed By: kamil

Subscribers: ashoat, tomek, ted

Differential Revision: https://phab.comm.dev/D8171