Created attachment 82750 [details] test case An absolute positioned element whose containing block is the viewport (initial containing block) has percentages for its margin-top computed based on the height of the viewport (instead of the width). Css 2.1:8.3 is formal in specifying that percentages for margin (and padding) are computed based on the *width* of the containing block. http://www.w3.org/TR/CSS21/box.html#propdef-margin In the testcase, the div has a 5% margin-top. Widening or narrowing the window horizontally doesn’t change the position of the block. Gecko and Opera behave correctly.
Created attachment 82755 [details] test case 2 There should be no red in this test case (resize window vertically…)
Reproduced with r79118.
I can confirm that this bug is still there. Tested on Safari 5.1.1 (6534.51.22) and Chrome 16.0.912.63
Created attachment 139552 [details] test case 3
Comment on attachment 139552 [details] test case 3 Tested on 30 April 2012 webkit night build on Mac OSX.
Created attachment 156378 [details] This clearly shows percentage as being calculated as 50% of height of parent, not width of parent. This shows margin-top configured relative to parent element. On compliant browser, the green box is outside the red box. On Chrome and Safari, the green box is fully inside of the red box. This clearly shows percentage as being calculated as 50% of height of parent, not width of parent.
I believe this has been fixed with bug 103246 and can be closed.
Yes this does work correctly now. Thanks! Tested with WebKit nightly @r137751, the attached test cases and my real world usage work as expected.