What is a continuous cover?
With a continuous cover, the spine of the book is also printed. This is a possibility for books that are bound with the adhesive binding method. Often, with a continuous cover, people choose to print the title of the book on the spine. In addition to the nice look of a continuous cover, that also makes it easy to find in a bookcase.
A continuous cover for your book?
If you want a continuous cover, you must upload a document for the entire cover as a spread. If you only upload a page for the front and/or back of the cover, the spine of the book remains white. More information on how to make such a spread can be found here.