Adding postcss-cssnext

[lukejpreston]

Postcss-cssnext does the auto prefixing and no one should have to change their project in order to use it. It then means people can start using newer css

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[lukejpreston]

Looking through the past issues:

• I don't feel it is the same as Optional Sass Support #78 as it is not an optional plugin and does not add complexity.
• Also I don't think you are locking yourself into postcss as in this issue Add postcss-use plugin #213. It is letting people write newer css with no configuration or changes

Pretty trivial low impact change allowing people to write next-gen css

[fson]

Adding postcss-cssnext was discussed in #130. The problem is that many of the plugins in cssnext are not stable enough (see #130 (comment)) to be included in Create React App. We can only ship transforms that are really stable and rock solid. At the time there was no consensus on what could be such a subset of transforms.

Adding support for experimental CSS features is not without complexity – some plugins implement features only partially, some implement an older version of the spec or have bugs. There is a risk of having conflicts when the actual spec is implemented in the browsers.