flex: 0 1 auto, cannot grow but can shrink when there isn't enough space
flex: 1 1 auto, can grow and shrink to fit available space
flex: 0 0 auto, cannot grow or shrink, AKA inflexible
flex: <positive-number> 1 0, can grow and shrink, extent of growth depends on flex factor
Authors are encouraged to control flexibility using the flex shorthand rather than with its longhand properties directly, as the shorthand correctly resets any unspecified components to accommodate common uses.