cheat sheets.

For element E:
  E[attr^="val"]         Attribute value which begins with "val"
  E[attr$="val"]         ... which ends with "val"
  E[attr*="val"]         ... with the substring "val"
  E:root                 Only if root of document
  E:nth-child(n)         Only if also the nth child of its parent
  E:nth-last-child(n)    ... counting from the end
  E:nth-of-type(n)       The n-th E element sibling
  E:nth-last-of-type(n)  ... counting from the end
  E:last-child           Only if last child (first-child is in CSS2)
  E:first-of-type        First E element sibling
  E:last-of-type         Last E element sibling
  E:only-child           If only child of parent
  E:only-of-type         If only child of type E of parent
  E:empty                With no text or element children
  E:target               Identified by browser via fragment identifier
  E:enabled              User interface element which is enabled
  E:disabled             ... which is disabled
  E:checked              ... which is checked (checkbox / radio button)
  E::selection           ... portion selected/highlighted by user.
  E:not(S1)              Not matching additional selector S1
  E ~ F                  With sibling F following (not immediately)