It's mostly: - "flex: 1 1 0px" for fill available space - "flex: 0 0 auto" for sizes to content And then arguably every flexbox item ought to have min-width

It's mostly: - "flex: 1 1 0px" for fill available space - "flex: 0 0 auto" for sizes to content And then arguably every flexbox item ought to have min-width (and/or min-height) set to 0 because flexbox has a "min content sized" automatic minimum size built-in, which is rarely what you want. But if the content isn't overflowing or can be compressed in some way then you can get away without this.