Created attachment 304560 [details]
See attached test case.
The align-items and justify-content properties seems to be completely ignored when the flex container is a button. It doesn't seem to matter if the flex direction is row or column, or what value you use for align-items and justify-content - setting them does not affect any change whatsoever.
Works as expected in Chrome, Firefox, IE11, and Edge. Fails only in Safari
Looks fine on Safari Version 11.0 (12604.1.38.1.7)
Created attachment 321277 [details]
Test run on safari 11
Created attachment 328444 [details]
Screenshot of actual output of Safari 8
Note the attached test case image is wrong. It shows the expected output instead of the actual output. I have attached a corrected screenshot of the actual output on Safari 8.
This does appear to be fixed in Safari 11.
Thanks for the confirmation.