[CSS] Ngrams Table, nested ngrams in groups
Children of Ngrams in Tree are too much aligned :
- In the table: https://dl.delanoe.org/groupTreeCSS.png
- In edition mode: https://matrix.org/_matrix/media/r0/download/matrix.org/XNtTgruhlYIzzZCakdOSEQDG/Screenshot%20from%202022-06-30%2009-51-02.png
Please test it for many levels of depth, it will be easier for user to use the ngrams table when seeing the Tree shape.