Hello gaetano liggieri,
While viewing the source code, some added CSS codes is appeared there? We believe that you haven’t added any CSS codes on Custom CSS, but have you edited any theme files from any method? Either from Editor of from FTP ? If not, it may be causing the issues with the plugin. Please try once by deactivating the plugin you installed one by one and try to figure out which plugin is causing the issues.
Please try it once, let us know otherwise.
Best Regards,
Acme Supports