Hi!
Yes, this was for the old edit modal, before action buttons existed. The right selector is not .MuiDialog-container (this is the selector for the exterior background of the modal) but .MuiPaper-root
. I will update the code accordingly.
Though using .MuiDialog-container (no .cssxxxx and with #blockId before) is indeed interesting to customize the text of the labels of the modals
For the button customization of the action modals => Customise "Save" Button Color inside a Modal - #6 by matthieu_chateau