4th Generation CSS inheritance - grand grand child theme

Question

I have a child theme that inherits magento luma, let's call it Theme A.
Theme B inherits from theme A,
and Theme C inherits from Theme B (By the way this is a multi-store so this is the reason behind all the inheritance structure requirements)

According to magento documentation
https://developer.adobe.com/commerce/frontend-core/guide/css/quickstart/customize-styles/

when i want a child theme to extend parent theme , i need to create this structure:

app/design/frontend/Vendor/
├── parent
│   └── web
│       └── css
│           └── source
│               ├── _extend-child.less (keep this file empty)
│               └── _extend.less
└── child
    └── web
        └── css
            └── source
                └── _extend-child.less
...

and this works when for Theme B extends theme A
but now Theme C need to extend theme B
and _extend-child.less in Theme B already contains code because those were
magento requirements for the time where Theme B needed to extend Theme A

Basically my question is how can i keep Luma,Theme A, Theme B styles(This is currently the existing behavior for all the existing Themes) and load additional styles of Theme C.