Adjust the styling of the Design Manual's header

[marteki]

When adding the Data Visualizations category to the Design Manual, we made some basic changes to the navigation menu to accommodate the new entry. We should take a closer look now at the styling of the new longer menu, including possibly tightening up the height of the header and aligning the site name's baseline with the logo's baseline.

Current navigation menu:

[Scotchester]

We might want to roll a proper responsive design strategy into this issue, as well. I kinda half-arsed it way back in the day.

This is not doing so good, Pearl:

[marteki]

@Scotchester Maybe mobile-first? 😉

[nataliafitzgerald]

@Scotchester @marteki I would love to "roll proper responsive design strategy" into this!