Putting the following on the grid container (grid element before): padding: 20px; doesn't add the top and left padding (see test case).
I misinterpreted the issue. The grid container is properly sized but the grid items ignore any paddings (and probably borders).
Created attachment 195216 [details] Test case, there should be some grey above and left of the colored squares
Created attachment 195468 [details] Proposed fix 1: Add the borders and paddings before / start.
Comment on attachment 195468 [details] Proposed fix 1: Add the borders and paddings before / start. Clearing flags on attachment: 195468 Committed r147140: <http://trac.webkit.org/changeset/147140>
All reviewed patches have been landed. Closing bug.