Not possible modify theme Platon

I've just installed the new version of Opigno (1.20). When I go to modify the theme Platon I can make changes but when I save I get this message: "Forbidden You don't have permission to access /admin/appearance/settings/platon on this server." Please help me to solve this problem. Thank you Roberto Eccher

Don't edit the Platon theme,

Don't edit the Platon theme, make a subtheme. You can rewrite everything in Platon via the subtheme. Follow this tutorial: