The following are elements, or CSS selectors.
They are what you are able to modify with code.
.avatar
profile pictures
a
image and text links
body
the element that contains the entire webpage; useful for backgrounds
div
a lot of things; see below for more detail
div.button_div
buttons, duh
div.menu_section
the foreground for each section
div.navbar
div.zebra
elements that contain chat messages in ShoutBoxes
.form_button
spoiler & buttons (save, post, send, refresh)
.form_textarea
where you type
h1
page titles
h1:after
add something after page titles
h1:before
add something before page titles
img
images
input.form_button
basically the same as .form_button, but more specific in case you want to override something
.menu_section
pages list as well as the top box that contains your avatar
tbody#text_comment
td
a row in the list of things that describe you in your user profile
td.title
the topmost row
td.title:after
to add something to the topmost row
td.title:before
to add something before the topmost row
textarea
also a place where you type
.alerts_popup
the small popup at the top of the page when you get a message or alert
div.alerts_popup
also the alerts popup, but more specific
the following are elements that i'm certain have used to function. most have probably been replaced with other elements, & others have probably been removed. i haven't tested them yet with current code.
.awesome
b_text_comment
.comments
div.head
div.row
form
.form_body
table
tbody
td.profile_pages
th
tr
span
.spoiler