The ability to manage Custom Form Styles is indeed tied to specific permissions in QuickBooks Online Plus, Rose.

Currently, only the Primary Admin has full access to these features, and users with the Standard (All Access) role do not have the functionality required to customize form styles. 

You can add your accountant as a Company Admin, allowing them to perform most tasks, including managing settings and accessing customized invoice templates. But, they will not have the ability to change or reassign the Primary Admin role.

Please review the user roles and access rights to understand the various options available.

Let us know if you have any further questions in the comments, and we'll be happy to assist you.