I don't use a standard theme, but I have added custom CSS into my theme for the same reason. I have two options -- one for just the page text, the other for the entire page itself.
/* Add Paper-Look to Book Module to JUST BEHIND the text on the book page */
[id=page-mod-book-view] div[role=main] .no-overflow {padding: 10px; background: #fff; box-shadow: -1px -1px 8px rgba(0,0,0,0.1), 1px 1px 0 rgba(0,0,0,0.1), 3px 3px 0 #fff, 4px 4px 0 rgba(0,0,0,0.125), 6px 6px 0 #fff, 7px 7px 0 rgba(0,0,0,0.15), 9px 9px 0 #fff, 10px 10px 0 rgba(0,0,0,0.175), 12px 12px 10px rgba(0,0,0,0.4);}
/* Add Paper-Look to Book Module to BEHIND the entire book page */
[id=page-mod-book-view] .region-main {padding: 10px; background: #fff; box-shadow: -1px -1px 8px rgba(0,0,0,0.1), -1px 1px 0 rgba(0,0,0,0.1), -3px 3px 0 #fff, -4px 4px 0 rgba(0,0,0,0.125), -6px 6px 0 #fff, -7px 7px 0 rgba(0,0,0,0.15), -9px 9px 0 #fff, -10px 10px 0 rgba(0,0,0,0.175), -10px 12px 10px rgba(0,0,0,0.4);}
