Draft: Apply typescale to runner

What does this MR do and why?

This change adds the required CSS to the "new runner" page to apply the typography scales recommended by Pajamas.

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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Related to #383139 (closed)