When a comma is involved in a ruleset, "the whole statement should be ignored if there is an error anywhere in the selector, even though the rest of the selector may look reasonable in CSS 2.1." CSS 2.1, section 4.1.7 Rule sets, declaration blocks, and selectors http://www.w3.org/TR/CSS21/syndata.html#q10 In other words: <style type="text/css"> .two { color: green; background: white; } #6ident, .two { color: red; } </style> <p class="two">This should be green.</p> because an ID selector can not start with a digit. http://www.w3.org/TR/CSS21/syndata.html#q6
The real issue at the source may be that Safari accepts, honors id selectors starting with a digit: http://www.hixie.ch/tests/evil/css/css21/tests/t0509-id-sel-syntax-01-f.htm
Bug 14373 is more accurate. *** This bug has been marked as a duplicate of 14373 ***