In another thread, DiapDealer said:
Originally Posted by DiapDealer
The stylesheet goes in the Styles folder. And you link each xhtml file (that you want to use it) to that stylesheet with:
<link href="../Styles/stylesheet-name.css" rel="stylesheet" type="text/css" />
in the head section.
My style sheet has its own file name (myfirstbook.css), but after I paste that file into Sigil, Sigil assigns it a new name "Style0001.css". So far, Sigil doesn't see my style sheet, even though it's right there in the Book Browser with the message "The resource is present in the OPF <manifest>, but it's not reachable (it's unused)". I'm not clear what Sigil is doing file-wise, so how do I ensure the text files see the style sheet as you've described it?