Spec: https://drafts.csswg.org/css-align/#propdef-place-content https://drafts.csswg.org/css-align/#propdef-place-items https://drafts.csswg.org/css-align/#place-self-property Note that the syntax has just been discussed on the CSS WG. Check the last comments on this issue before implementing them: https://github.com/w3c/csswg-drafts/issues/595#issuecomment-262709407
All the shorthands, place-content, place-items and place-self have been implemented, so we can close this bug now.