I set a Code Block with css at the top of the main template.
The css is correctly apply, but I can't edit this css. When I load the template from Wordpress backend, the left side of screen is empty and I don't know where to find the block I created.
Can you, please, help me to search at the good place.
Not sure if you already resolved this. But you can open up the structure panel (in your screenshot the little icon on the top right) and then click on the code block. Then you will see the option to edit it.