[Overlay token] Update website docs

[laurenmrice]

Acceptance criteria

• Update the website Elements > Color > Tokens tab page with the new values for the current $overlay color token.
• In VsCode, in the left hand nav, navigate to src > data > guidelines > color-tokens.js and command+f to search for the $overlay color token. This is where you will change the values to the following:

White theme	Gray 10 theme	Gray 90 theme	Gray 100 theme
Black	Black	Black	Black
#000000 @ 60%	#000000 @ 60%	#000000 @ 60%	#000000 @ 60%

• Make PR
• Review
• Merge PR

[github-actions]

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