Ok, this is an issue from Toolset and not WP Grid Builder.
Toolset does not target it's own elements (with a class or id for example) but apply CSS to any element in the admin.
This is consider as a bad pratice and should be avoided by plugins and themes.
The best is to report this issue to toolset plugin author directly.
Would it be possible to provide a copy of the plugin as well as the steps on how to replicate the issue so that I can creae a test site for our team to investigate?