New design for the FreeBSD website

Light/dark modes match the environment. The largest asset on the home page is 78K. When toggled visible, the top menu doesn't create a fiddly overlay, it just pushes other content down. Great taste, less filling!

All I can fuss about is that the menu remains hamburgered all the way up to about 1300px window width. A modestly sized desktop browser window, say 1000px, should still get the desktop version imo.

First two nits I've noticed:

• drop-down menus don't highlight hovered items
• label of "❤️ Donate" button is not centred within its container bounds