Theme overrides example

[robinnorth]

Hi @bmartel, thank you for your super useful component! Would you consider adding an example of how to override the base MultiSelectTheme in the same way as you are able to do with built-in Chakra components?

Perhaps I'm missing something, but I haven't been able to work out a simple way to do so in order to change the control's focussed outline color, so it feels like an example in the documentation or the sample implementation would be very helpful indeed.

[blascokoa]

Same issue here, not able to override the default theme in a simple way.

Thanks for your work @bmartel!