22474 2013-06-26 13:10:05 +0000 Percentage top and bottom property does not always refer to the height of containing block 2013-06-26 13:10:05 +0000 1 1 1 Unclassified CSS CSS Level 2 unspecified All All NEW P2 normal --- 1 curvedmark bert public-css-bugzilla oldest_to_newest 89885 0 curvedmark 2013-06-26 13:10:05 +0000 From http://www.w3.org/TR/CSS21/visuren.html#position-props the spec says: > <percentage> > The offset is a percentage of the containing block's width (for 'left' or 'right') or height (for 'top' and 'bottom'). But test case http://jsbin.com/ocadip/18/edit show that for all major browsers, when a relatively positioned box is inside an absolutely positioned box, it's percentage top property resolves to zero. From the discussion at http://lists.w3.org/Archives/Public/www-style/2013Jun/0473.html it appears that if a relatively positioned box's containing block doesn't have an explicitly specified height value the top and bottom property of that relatively positioned box, if they are of a percentage value, should compute to zero, which works much like the height property. So I think the spec should at least mention that.