Fix: A11y - Use a darker contrast-compliant gray

[machikoyasuda]

closes #389

Use tertiary-gray instead of seconday:

I'm going to keep the secondary variable for now, in case we use it for non-text things like borders, etc.

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[thekaveman]

I'm not sure why our code formatting has been changing lately? Is it a missing plugin? Or a new version that formats differently?

[thekaveman]

Thanks 😅

Even for small PRs like this, we want to keep things as clean as possible!