Hi Armands,
I havnt checked out the graph html yet, but it should be possible.
there are 2 ways to go about this.
here are some links that might help you out:
how to start styling in MX with sass
https://docs.mendix.com/howto/front-end/style-with-gulp-and-sass#1-introduction
how nth child works
https://css-tricks.com/how-nth-child-works/