How to get ThemeProvider in MUI BaseUi working

Question

I was trying to create a themed app with MUI BaseUi using ThemeProvider and createTheme as described in the docs. But in my app the theme is not used.

I am using @mui/base 5.0.0-beta.8 together with @mui/system 5.14.1 and @emotion/react 11.11.1

App.tsx:

import { ReactElement } from "react";
import {ThemeProvider} from "@mui/system";
import {myTheme} from "./themes/mytheme.tsx";

export default function RdApp(): ReactElement {
    return <ThemeProvider theme={myTheme}>
        <div>Hello world</div>
    </ThemeProvider>
}

thems/mytheme.ts:

import {createTheme} from "@mui/system";

export const myTheme = createTheme({
    typography: {
        fontFamily: "Arial"
    },
});

CodeSandbox: https://codesandbox.io/p/sandbox/dry-dew-z593g5