Cannot use function values or function rules in TypeScript

[16oh4]

Expected behavior:
Function values and function rules should render the appropriate CSS.

Describe the bug:
The rule which includes a function does not render. This is the typescript error (for function rules)

Index signature is missing in type '(data: any) => { backgroundColor: any; width: number; height: number; }'

Codesandbox link:
Please create a codesandbox.io with the issue. Make it as minimal as possible as this will help us find the bug quicker.

https://codesandbox.io/s/nifty-visvesvaraya-7eq2v?file=/src/index.ts

Versions (please complete the following information):

• jss: 10.1.1
• jss-plugin-camel-case: 10.1.1
• Browser [e.g. chrome, safari]:
• OS [e.g. Windows, macOS]: Windows 10 (Also present in CodeSandbox)
  Feel free to add any additional versions which you may think are relevant to the bug.