title: MUI v5 @mui/material/styles vs @emotion/react
body: <p>This is a follow-up question, to <a href="https://stackoverflow.com/questions/69629346/mui-v5-theming-with-emotion-mui">this</a> question about theming MUI v5.
  Although my questions were answered, I'm still having difficulties understanding where exactly the <code>@emotion/react</code> API and when the <code>@mui/material/styles</code>  should be used.
  I read to the <a href="https://mui.com/guides/migration-v4/" rel="noreferrer">migration guide</a>, while this does answer some 'how to' questions, I don't understand the bigger picture.</p>
  <p>When do I use MUI's styling, when emotion's? Why are there two styling solutions? Should I use MUI's <code>ThemeProvider</code> or Emotion's? What are the differences?
  These questions might be trivial to an experienced user, but as someone who's just getting started this is all a lot to take in and understand.</p>