I can´t reproduce your issue, i would need more information about what you're experiencing.
Have you tried the Kanban board in a brand new space without other customisations plugins space-styles?
I also noticed is that your button have other style than how it should really look like, this can be either an incompatibility of some css rules with your browsers (are your browsers up to date) or some other underlying cause.
Yours:
Correct:
i tried to reproduce your issue, but on my side everything works fine: