Opera developers are extremely thorough and hence slow at reviewing the updates to extensions. The process can take months. Simply install Stylus from Chrome Webstore as explained below.

1. Install a helper extension written by Opera Software to enable direct installations from CWS in Opera up to 76.0.3995.0:

   

2. Open Stylus in Chrome Webstore

3. Click Add to Opera button (or icon in address bar)

4. Wait a bit, open the extensions manager (Ctrl+Shift+E in Windows) opera://extensions

5. Click Install button in the Stylus entry