Navigation lacks clear hover / focus interaction states

[alexgibson]

STR:

1. Open https://main--mozilla-rise25.netlify.app/
2. Click "See the Winners"
3. Hover over the category navigation links with a mouse, or tab to the links to focus them

Expected results:

Both hover and focus states should clearly indicate which link is selected.

Actual results:

We do get a mouse pointer change on hover, but it's not easy to spot. The links are also small and not so easy to click. Similarly, we get a default outline on focus, but it's very small and at the start / end items is also partially obscured.