Feature Request: Apply theming to Invidious/Piped?

[Handrail9]

Hello, I am opening this feature request as I am a Gen-Z person who has nostalgia for the old YouTube layout, however I do not have enough nostalgia to recreate a new Google account and start handing them my data again.
I'm requesting this extension apply custom CSS to Invidious, Piped or both to allow these privacy-respecting youtube proxies to look like classic YouTube.
I understand if this will not be implemented or not planned as I am asking for the project to support separate third party websites, but it would be so awesome to see. Thank you for considering my request

Additional Information
Invidious' Project Website: https://invidious.io/
Piped's Project Website: https://docs.piped.video/
A Public Invidious Instance: https://inv.tux.pizza/
A Public Piped Instance: https://piped.video/
Another project that changes Invidious' UI Materialious