I apologize in advance if this question has already been asked, but, despite the vast number of information on the subject, to find the answer to your question, I couldn't.
The essence of the following:
For example, I have two separate scss file header.scss and footer.scss. The footer styles are almost identical with the styles of the header, except for a couple of properties.
But if I write it in the file footer.scss @extend header styles header can't be used because it is a different file.
Tell me how ideologically rather do in this situation? To a new class/item received styles of an existing class from another file, + added or changed some of the styles on their own.