This patch sets the @page margin sizes in epubs, overriding any @page margin set in the book's CSS stylesheet (but not in the XPGT stylesheet, see below). By default the top and bottom margins are set to be adjustable, their size similar to the left/right margin size set by the adjustment slider. There are options to set the top and/or bottom margin to a fixed size instead. Note that @page margins are seperate from (and overlap) both the body margins set in the book and the left/right margins set from the adjustment slider, and are added to any page margins set in the Adobe XPGT stylesheet if the book has one (e.g. page-template.xpgt). For this reason you might want to consider using the Modify ePub Calibre plugin to remove any body margins and XPGT stylesheet margins before sideloading the book, or perhaps enabling the `Ignore ePub Adobe XPGT stylesheet (page-template.xpgt)` patch. Also note that a side-effect of this patch is that the body padding-bottom is removed from the built-in stylesheet, which means that there will no longer be a blank line added automatically at the end of chapters. See at the bottom of the patch for replacement values that can be used to tune the size of the margins to suit different devices and reading modes.