TS: Error with @font-face and @import rules in globalCss function

[mateuszaliyev]

Bug report

Describe the bug

Using @font-face and @import rules in globalCss function results in type errors.

To Reproduce

https://codesandbox.io/s/withered-meadow-j4hcj

Expected behavior

No type errors as it used to be in previous releases.

System information

• OS: Windows 10
• Version of Stitches: 1.2.0
• Version of Node.js: 15.14.0

Additional context

I stumbled upon this error while working on my Next.js project after updating from v1.1.0 to v1.2.0. I've managed to reproduce the error using Code Sandbox with React TypeScript template. I'm pretty sure the bug is related to changes made in #793 though those type definitions are too complex for me to come up with a fix.

Error message produced by TypeScript is quite long. There are two sentences that stand out in my opinion:

Property '"@font-face"' is incompatible with index signature.
Types of property 'filter' are incompatible.

With @import rule both string and string[] values result in type errors whereas @font-face rule only produces an error with array of objects. Additionally hovering over @font-face key in VSCode shows that it is of type unknown while I believe it should actually be AtRule.FontFace | AtRule.FontFace[].