Extend Magento Luma theme less

Question

When extending Magento Luma less files in one children theme, what exactly is the name and the complete structure of the "parent" folder (mentioned at https://developer.adobe.com/commerce/frontend-core/guide/css/quickstart/customize-styles/#extend-parent-styles) ?

I find the documentation very fuzzy here and I need help with this. I only can assume at this point we don't want to add the new file _extend-child.less on core parent theme folder.

Thank you very much in advance! See below the diagram from the documentation link.

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

Answer 1

Since the Luma theme does not have <luma theme dir>/web/css/source/_extend.less, you don't need to do anything with Luma's theme folder, just create <your theme dir>/web/css/source/_extend.less, then your theme will extend Luma theme (and Blank theme which is the parent of Luma theme) properly.

The diagram and the case mentioned in the documentation you are mentioning are for the parent theme (called theme A) that extends theme Blank and has web/css/source/_extend.less + the child theme (called theme B) that extends theme A and has web/css/source/_extend.less