How to create insertion point to mount styles in shadow dom for MUI material v5 in React custom element

Using @material-ui/core V4(4.12.3 to be exact) I HAD a custom element created successfully using webpack and babel. I used to be styling it using the @material-ui/core makeStyles. Now I am upgrading to @mui/material v5 and want to use the built-in components from @mui/material but they do not display styled within the custom element.
Please note that I need this to be a custom element as it will be integrated within another hosting app.