fix: dark mode and header text display issues

[lucaseduoli]

This pull request includes several fixes to address dark mode not starting with the browser saved variable and the addition of the "Last saved at" text on the header. It also fixes some CSS issues related to the header display.

[github-actions]

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_{Last Modified at 13 Aug 24 22:17 UTC}

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[anovazzi1]

LGTM