Improved the declared types related to Stylis (#2493)

Author: Andarist

.changeset/itchy-waves-beg.md

@@ -0,0 +1,5 @@
+---
+'@emotion/cache': patch
+---
+
+Improved the declared types related to Stylis. This should improve the compatibility with the types published in `@types/stylis`.

packages/cache/types/index.d.ts

@@ -7,9 +7,10 @@ export { EmotionCache }
 export interface StylisElement {
   type: string
   value: string
-  props: Array<string>
+  props: Array<string> | string
   root: StylisElement | null
-  children: Array<StylisElement>
+  parent: StylisElement | null
+  children: Array<StylisElement> | string
   line: number
   column: number
   length: number
@@ -20,14 +21,14 @@ export type StylisPluginCallback = (
   index: number,
   children: Array<StylisElement>,
   callback: StylisPluginCallback
-) => string | undefined
+) => string | void
 
 export type StylisPlugin = (
   element: StylisElement,
   index: number,
   children: Array<StylisElement>,
   callback: StylisPluginCallback
-) => string | undefined
+) => string | void
 
 export interface Options {
   nonce?: string