The problem is on CSS in RVSitebuilder current version (5.2.10). We'll fix it in next version (5.2.11) and release very soon.

You can contact your host provider to do the temporary solution by making backup the following file:

/home/{user}/.rvsitebuilder/projects/{project_id}/customcss/{template_folder}/style.css.bk

Before preview and publish the project.