In profile preferences, allow a dark/light/system mode to change Community to Dark/Light/System for UI.
Thanks for the request, @Brian_McLeer. Introducing a Dark Mode or Dark Theme for Esri Community is something that has come up in conversation in the past. The interest is something we'll keep in mind if/when our platform vendor makes this type of feature possible.
The Dark Reader extension works well for me.
Thanks for pointing out that option, @JonM32. @Brian_McLeer, if you end up deciding to give that a go we'd love to hear if it satisfies what you're looking for.