Adjust page size in books
You can now adjust page size in books with the new zoom feature. Select a preset size to see your content at that magnification level. You can also resize the page view to fit the page or fit to width of your window. In both cases, the page size is responsive and automatically adjusts to fit the page or window when you resize your window.
You can change the layout position of a book in Edit mode on the General tab under Properties.
You can also set a default zoom value for your book under Properties so that it always opens in the selected size.
When you enter full screen mode, your zoom value is overridden and the page size changes to Fit to page to allow you to see the full contents of your page. However, you can still change your zoom value in full screen mode. When you exit full screen mode, you automatically go back to the previously selected zoom value.