please How can I change the font size of the x-axis and y-axis, it can be through css or another way.
There's currently no way to do this through Kibana. There is an open issue here which you're welcome to comment on. It may be possible to configure custom css to do what you're referring to however there's no official support or documentation for this. With that said, there's nothing stopping you from inspecting and modifying the css to see what you can do.