The plugin will show up in the left-side menu only for users with the “Admin” or the “Web Designer” role. You can remove the plugin from the menu for a specific user or role by using a plugin similar to Members or User Role Editor and by removing all the “*_custom_css” capabilities assigned to the user or the role.
There are 10 “*_custom_css” capabilities in total. By default the 10 capabilities are assigned to the “Admin” and the “Web Designer” role.
After making the capabilities and roles changes you are free to uninstall the Members or the User Role Editor plugin. The plugin is only an interface for the Roles and Capabilities functionality from the WordPress core.