[Kralik]

I've done the Calibre ePUB-->ePUB trick before but I'd rather not muck with it every time I switch reader firmware or readers. So here's what I have for the userstyles.css (changes from yours):

@page {
  margin: 0.5em !important;
  padding: 0px !important;
}

html, body, p, 
p.indent, p.nonindent,
p.text, p.cotx, p.tx, p.tx1, p.int,
div.preface {
  font-family: "droidserif", sans-serif !important;
  padding: 0px !important;
  margin: 0em 1.2em 0em 0em !important;
  text-align: justify !important;
  line-height: 120% !important;
  font-size: 18px;
}

body { margin: 0px; }

I like a consistent font size and using em wasn't doing it from book to book. So, it's 18px, which is nice to read at 100% zoom. Margins are as I like them and leave just enough space for 3 digit page numbers. Images display correctly at 100% (except for some title pages that are overstretched, such as Feedbooks' logo).

All that I will need to do from book to book is add any p.this and p.that and p.whatever. Header tags don't work quite right, so they usually end up a tad smaller than the normal text, but I can deal with it. I'd rather not have to try to cover all of the header classes...