Hello,
Apologies about the Inconveniences caused! However, to properly check what is causing the issue, we need to check Live URLs as there might be many possible issues for the error including incorrect codes or invalid CSS Codes.
So, whenever you are ready, please provide us with a Live URL and we will definitely check this out for you. Thanks for your Patience.
Also, you can consider checking out the Position of the Colors CSS required for correct theming: http://docs.semicolonweb.com/docs/getting-started/color-schemes/
Meanwhile, do let us know if we can help you with anything else or if you find any further issues with Canvas.