Upgrade PostCSS to use v8

[jeremyzilar]

Any thoughts on upgrading to use PostCSS v8?
It is currently a default dependency in Storybook and once we started using React Toastify, it started causing build issues in our storybook, mainly because Toastify uses ^7.0.27

[jeremyzilar]

I tried adding postcss to 8.3.10 under a resolution section in my package.json, to force v8 on all packages,

"resolutions": {
    "postcss": "8.3.10"
  },

but it breaks toastify.