Originally Posted by theducks
I assumed the block was: the display page: and I wanted the dingbat not to exceed 10% of available Height (780+px ) (actual size 298)
That's one of the problems with CSS in ePUB, there's no way to refer to the actual display page/screen size (height or width). The containing block is usually <body>, and it takes the width of the page (so width references typically work as expected), but its height is unspecified and adapts to its contents. Could you consider specifying your image's height in ems? It will change when changing the font, but that may be good too.