How to quickly set up styles for multi-level numbering headings

This topic is specifically written in a personal diary, as I doubt that it will be useful to a lot of people. By and large, the whole essence of the topic in one useful office opportunity is to change the style in accordance with the selected text fragment. Consider the simplest example of how this can be applied.
Let's say we have a document already written by someone with a large number of headings.



You want to change the heading styles so that they are numbered according to the heading level.

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Select one of the headings of the first level and add numbering to it.



Not bad, but the numbering applied to a specific paragraph, and not to the whole style.
We will use the function of bringing the style in accordance with the selected fragment and make sure that all the headings of the first level are numbered.

Repeat the same for the second level headings:



Choose the second numbering level:


Similarly, we update the style:


Beauty:


Last, third level:






On the last screenshot see the final result. I was a little mistaken and the last line is actually the second level heading :)


Ps. Dedicated to N. :)