Update focus outline color so it coordinates with our branding

[MelSumner]

We're using the default focus outline at the moment, but we need to update the color so it meets the following criteria:

1. it meets color contrast criteria for accessibility purposes (so it should show up on light and dark backgrounds as appropriate)
2. it coordinates with our brand and design

Note that focus outline should never be hidden or removed.

[mansona]

@MelSumner I had a discussion with @pichfl about this and we might need to have a discussion about secondary colours before we can (easily) fix this 🤔

I don't see a blocker tag on this so can we move it to the Phase 2 board?

[takshch]

Can you please tell me whether Secondary colours are already discussed or we need to discuss it?