There is quite a difference between css flexbox and the one implemented by Facebook. Lots of things in common but defaults are very different. Specifically:
Everything is display: flex by default. All the behaviors of block and inline-block can be expressed in term of flex but not the opposite.
flex: attribute is only used when at the same level there are few components with different flex values (flex: 1, flex: 3) means that the second element should be 3 times bigger than the first one. flex attribute is the only one supported (no grow/shrink support).
More info: https://github.com/facebook/css-layout