A screenshot of MakerWorld in dark mode
From MakerWorld.com

If you opened MakerWorld and found something was different but couldn’t tell what, it probably was the new dark mode! In an update that arrived on January 1st, 2025, MakerWorld released a new dark mode that will follow your system preference by default.

However, if you don’t like it, you can always go to your preferences (https://makerworld.com/en/my/settings/preferences) and select the theme you prefer.