This theme is no longer being maintened. Please read: Please don’t theme our apps
Make sure you have the "User Themes" extension turned on.
To install, copy the Myopia folder and paste it in ~/.local/share/themes or ~/.themes, and select the theme in Gnome Tweaks.
There are some variations of this theme on the 'Variations' folder ;)
Make sure to tweak themes inside the original Myopia-Theme repository.
You can customize colors, transparency and other stuff in the file Settings.scss (Inside the 'Tweaking' folder). For advanced tweaks, use the Advanced folder.
Then, inside the 'Tweaking' folder, open the terminal and type ./parse.sh, this will recreate the 'Myopia' folder with your new settings.
After all of these steps, follow the Installation guide to get your new Myopia customized theme ;)