CSS Flexbox model is optimised for UI Design.
It is developed primarily to avoid overflowing parent element. It will shrink children when ancestor element size is constricted. It will fill the space by expanding child element's size when ancestor element size extends.
Flex container shrink and expand behaviour can break with min and max width / height property.
CSS FlexBox versions by version
W3 2009 : display: box;
box-align start | end | center | baseline | stretch
box-direction normal | reverse | inherit
box-flex <number> 0.0
box-flex-group <integer> 1
box-lines single | multiple
box-ordinal-group <integer> 1 visual
box-orient horizontal | vertical | inline-axis | block-axis | inherit inline-axis box elements no no visual
box-pack start | end | center | justify
W3 2011 : display flexbox | inline-flexbox
flex-align auto | baseline auto
flex-direction lr | rl | tb | bt | inline | inline-reverse | block | block-reverse flexboxes no lr | rl | tb | bt
flex-order <integer> 1
flex-pack start | end | center | justify
W3 2012 : display flex | inline-flex
align-content flex-start | flex-end | center | space-between | space-around | stretch
align-items flex-start | flex-end | center | baseline | stretch
align-self auto | flex-start | flex-end | center | baseline | stretch
flex-direction row | row-reverse | column | column-reverse
flex-flow <'flex-direction'> || <'flex-wrap'>
flex-grow <number> ‘0’
flex-shrink <number> ‘1’
flex-wrap nowrap | wrap | wrap-reverse
justify-content flex-start | flex-end | center | space-between | space-around
order <number> 0