Hello,
We do not stylize third party components. Our templates include a basic bootstrap that is meant to stylize the core Joomla components. A component is responsible for styling itself, and should not be relying on the template. If there is an issue with the component's theme, then there is either missing or incomplete css for that theme. I have looked at several Kunena themes and that has been the case.
I have an issue with this response. After spending hours trying to troubleshoot issues with Kunena log-in form not working (you can't type in the fields), I have discovered that the Kunena login form works fine with the Protostar template, along with a Rockettheme template that I use on another site. There is some sort of conflict between Kunena and the Shape 5 templates (I have actually tried two different Shape 5 templates with the same result.) You can see what I mean by going to
http://crazysuzy.co/forum/index and trying to use the log in forms (either one). I have also tried enabling and disabling your register and log in modules, but that has not made a difference. Here is how Kunena 5 looks on a site that does work:
https://cal4wheel.com/forum/index (running Rockettheme).
Also, the Kunena 5 themes come with their own bootstrap support that can be disabled. I have tried enabling and disabling bootstrap on the Kunena template and it has made no difference.