Default to primitive CSS variable values for SASS typography line-height and size

[iansan5653]

What are you trying to accomplish?

The typography SASS variables for font sizes align with the primitive CSS variables in value, but the default line-height differs. This results in inconsistent spacing in body text - for example, the Markdown editor uses the 1.4285 value while the markdown-body class uses 1.5, resulting in inconsistent spacing across the Markdown preview vs editor (as noted on Slack).

What approach did you choose and why?

To fix this, we can update the value for lh-default to match the primitive. To ensure future consistency I updated it to be the primitive. I also updated the small & default font sizes to use the primitives as well (this has no visual change). This reduces the line-height by 0.0715 (1.001 px).

Note that I did not update lh-condensed and lh-condensed-ultra since there are no existing primitives that match these values (that I know of).

What should reviewers focus on?

Can these changes ship as is?

• Yes, this PR does not depend on additional changes. 🚢

[changeset-bot]

🦋 Changeset detected

Latest commit: aa88388

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

This PR includes changesets to release 1 package

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@primer/css	Minor

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[langermank]

This change scares me a bit 😆 I think changing that default line-height could lead to visual changes which could be both good and bad depending on the context. What if we just update the CSS specific to markdown to isolate the fix? Not a global/long term fix really but these older files typically need a lot of testing to change.

[iansan5653]

Would it be enough to deploy this to lab and test it out? It is a very slight change (1 pixel) and it seems generally good to align on one line height and discourage inconsistency more broadly