New button in code / markdown cells

[Aevox]

Good evening,

I’m trying to add a new button in the following marked area:

However, so far I’ve been failing at it.
I’ve managed to add a button in the toolbar and also somehow below the cell in which I want to add it.

Does anyone know how I can add a corresponding button?
If possible, a code example would be lovely.

Kind regards
Aevox

[spookster]

There are some examples at the extension-examples repo over on github.
You probably want the cell-toolbar example here.