How to connect your template (based on the default one) in openCart 3x?

Question

opencart

Acted according to this instruction ( here ). Created a duplicate of the default template and made recursive changes. (tried recursive change with and without theme_ prefix). I have a Russian assembly, made the appropriate changes both in the en-gb folder and in ru-ru. But in the system-settings-site(ed)-theme "my new" theme did not appear. Surely someone has come across this. I try everything locally, openCart 3.0.2.0, there is only one entry in the error log "2018-08-21 9:09:32 - PHP Notice: Undefined index: code in D:\wamp\www\testshopru.local\admin\model \design\layout.php on line 38" and she, IMHO, is off topic.