The EPUB file format uses standard CSS 2.1 without some elements to change the way book presented.
See http://www.w3schools.com/Css/default.asp for CSS tutorial.

FB2 standard include some elements are absent in XHTML standard used in EPUB files.
To preserve "special" representation of such elements in resulting EPUB such element marked with "class" attribute that you can
style with CSS.
Here is the list of the "class" attribute values used and their meanings:

"annotation" - FB2 annotation element

"body_image" - FB2 image defined on top of main body

"pre.code_fix" ("code_fix")  - set only on "pre" elements used to workaround [code] element problem (wrap them)

"citation" - FB2 citation element

"citation_author" - FB2 citation author element

"drop" - related to capitalization of section's first character, span.drop - controls the first character itself, while p.drop - the trailing text

"empty-line" - FB2 empty line element

"epigraph" - FB2 epigraph element

"epigraph_main" - same as above but only for main (book) epigraphs

"epigraph_author" - FB2 epigraph author element

"ex_bad_link" - ex-bad link that get converted to SPAN element in case had text content

"fb2_info" - FB2 Document Info section transferred to EPUB as a page

"int_image" - FB2 inline image element

"normal_image" - FB2 image element that not section image and not inline image

"note_anchor"  - anchor back to main body in FB2 "notes" body section

"note_section" - section in "notes" FB2 body (usually contains one note) 

"poem" - FB2 poem element

"poemdate" - date in the FB2 poem element

"poem_author" - FB2 poem author element

"poem_subtitle" - subtitle in FB2 poem

"poem_title"  - title of poem

 "poem_epigraph" - epigraph of poem

"section"?  - where "?" is a number starting from 1 - FB2 file section, the number shows the level of inclusioon: 1 - top level section, 
                 2 - section included in section level 1 etc.
                 
"section_image" - FB2 section image.

"stanza" - FB2 stanza element

"subtitle" - FB2 subtitle element

"title"? - FB2 title element where ? - number starting from 1 defines level of inclusion, 1 - top level title (body) , 2 - title of it's subsection , etc


"v" - FB2 "v" element (paragraph in stanza)



Here are style classes specific to cover page only:

"coverpage" - coverpage main section (page)
"coverimage" - coverpage image




Here are style classes specific to TitlePage only:

"titlepage" - title page main section (page)
"title_series" - (applied only to h3 on title page) used to style series on Title page
"title_authors" - (applied only to h3 on title page) used to style authors on Title page




Here are style classes specific to About page only:

"about"   - about page main section (page)

