Step 1: Create the theme

1. Create a bosco-blocks directory inside of themes.
2. Add a style.css and theme.json file as shown below.
3. Create a templates directory, and add an empty index.html file.

The theme directory should look like this:

Step 2: Test

1. Activate the theme, and check that no errors are displayed.
2. Go to the site editor, and check that no errors are displayed.

Code

style.css

theme.json