[BUG] FronteggProvider.customStyles are not applied to admin box

[iurii-iufimov-forgood]

Describe the bug
While creating <FronteggProvider> component you can pass customStyles property. It is applied to the shadow-root of login-page element, but not to the shadow-root of admin panel.

To Reproduce

const customStyles = `
.MuiBox-root {
  background: #000
}
`;

const root = ReactDOM.createRoot(document.getElementById('root') as HTMLElement);
root.render(
  <React.StrictMode>
    <FronteggProvider
      contextOptions={contextOptions}
      hostedLoginBox={false}
      customStyles={customStyles}
    >
      <App />
    </FronteggProvider>
  </React.StrictMode>
);

Expected behavior
Whether customStyles should be applied to all shadow-roots, or them should be configurable only for loginPage (e.g., via themeOptions.loginBox)

Screenshots