Homepage and header spacing updates

[joshdarby]

Changes

This pull request makes the following changes:

• Decreases site header margin down to 1.5rem
• Removes padding from the main navbar
• Reduces bottom-margin styling for homepage widget titles to 2rem from 3rem
• Decreases before-footer wrapper area bottom padding to 1rem

Why

For #76

Testing/Questions

Features that this PR affects:

• Site header spacing
• Main navbar spacing
• Homepage widget title spacing
• before-footer area bottom spacing

Questions that need to be answered before merging:

• [ ] Is this PR targeting the correct branch in this repository?

Steps to test this PR:

1. View the homepage on desktop and mobile and make sure none of the spacing updates messed anything up

[benlk]

Using the 1025x789 browser dimensions given in https://www.whatsmybrowser.org/b/4WJEB, a couple of concerns:

• it looks like there's extra space beneath the main menu
• the global nav wraps onto a second line

Decreasing the global nav font size and header donate button font size to 16px clears things up down to around 993px, when the problem reoccurs until 979px when the header social buttons are hidden.

Reducing to 15px solves the problem until 825ish px, where the problem remains until 768px when the global nav is hidden and moved to the main menu.

[joshdarby]

@benlk That should all have been solved in #81 (since it's caused by the original header font being removed from Adobe Fonts)

[joshdarby]

The above should be solved now that I merged master in