By default, Ecwid automatically adapts store colors to your website, but this does not work perfectly in every case.
If your Ecwid store does not match your SimDif theme, you can override it in Ecwid. Just create a new theme in your Ecwid account and adjust your store colors, fonts, and other details to your liking.
Click here to see Ecwid's guide on this topic.
If you need further support, feel free to contact the Ecwid team directly.