Though our aim is to make our integration work with as many themes as possible, we cannot guarantee full compatibility with every theme.
It is unlikely that you will encounter CSS issues with Autocomplete. If you do, please reach out to us on our forum so we can further improve Autocomplete to be fully theme-independent.
If your theme is not fully compatible, it is more likely that you would have to adapt your CSS when using our replacement search page as there are more factors required for out-of-the-box compatibility.