are you running calypso to process the created class? if you don’t run calypso locally, the class is not added to your directory, resulting in it not being available in your front-end:
other options to try as well is running a nanoflow instead of JS
I had a similar error when I had the cell styler inside a container below the data grid. The problem went away when I moved the cell styler out of the container so it was on the same level as the data grid. You may want to try removing any containers around the cell styler that don’t encompass the data grid.