flexbox is a CSS flexible box layout module, and the standards are constantly changing during the development process:
display:box,box-{*} is the 2009 version of flexbox
display:flexbox, or the function flex(), is a strange hybrid in 2011
display:flex, flex-{*}, is the standard released in 2012 that is currently in use
The trend is of course to follow the latest standards, but the front-end issue must of course be decided based on the support of the browser. If the lower version of the browser only supports the old standard, and we need to support For this part of the browser, you must also write it, but their usage is still very similar, so for the sake of compatibility, it is understandable to write it at the same time.
display:box,box-{*} is the 2009 version of flexbox
display:flexbox, or the function flex(), is a strange hybrid in 2011
display:flex, flex-{*}, is the standard released in 2012 that is currently in use
display:box box-flex is an early use of flex layout, it is no longer standardized, display:flex is standard