Here is a collection of userscripts I have made!
You will need a browser extension such as Tampermonkey. Click the link to the userscript and you will be taken to the repository for the code. In the readme.md there will be a link to install the userscript. Click it and follow the instructions to install the userscript.
My best dark theme for Scratch 3.0Check it out
Dark theme for Scratch 3.0Check it out
Make Scratch 3.0 have Scratch 2.0 block colorsCheck it out
I Can't Believe It's Not 2
Make Scratch 3.0 look like Scratch 2.0Check it out