New `light` and `dark` neutral scales

[langermank]

Introducing... new light and dark neutral base scales! 🎉

This isn't technically a breaking change and there should be very little visual differences right now, but we'll be releasing this in Primitives v9 since its a new way of approaching neutral base scales.

Changes

Inverted scales

Going forward, our base scales will follow a reverse pattern where 0 is the lightest value in light and the darkest value in dark. This makes it easier to maintain and use for functional tokens where in many cases, both light and dark themes will be identical in base value.

Two scales to rule them all

Rather than maintaining separate high contrast scales, we now have only two scales that handle low, medium and high contrast. We adjust contrast by moving up and down the scale, like darker background shades or darker text shades for light high contrast.

Contrast ratios and application

Each step of the scale serves a purpose. The first 5 shades are primarily background shades, 6 and 7 are borders, and 8 to 11 are for text.

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 87053dbfddb7bf5a78f18cf773737d0e72e639d7

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/primitives	Major

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[lukasoppermann]

Can we fix this in here or would it better be a separate fix?

Hover state of button

I think the fix would be a using black with a very low alpha, like 0.1 or even lower.