A previous version of the Flexbox spec set the static position of abspos children as if they were a 0x0 flex item. However, the latest version of the spec takes them fully out of flow and sets the static position based on align and justify properties. (The static position is used when there are no top: or left: or related properties used to position the absolute-positioned element. See the sample below.)
Docs: https://developers.google.com/web/updates/2016/06/absolute-positioned-children
Samples: https://googlechrome.github.io/samples/css-flexbox-abspos/index.html http://jsbin.com/sikiqedemo/3/edit?html,output