I am implementing a rich text editor into NetlifyCMS and went with the react draftjs wysiwyg.

I can implement the text editor as a normal component and put it into a page. CSS classes work fine there because Gatsby uses css-loader from webpack by default. But, css-loader doesn't seem to work in NetlifyCMS.

What I have found is that the Gatsby/NetlifyCMS combo doesn't allow the css-loader to work in the NetlifyCMS environment. I know that some people with similar issues have gone into the webpack config and adjusted the modules option for the css-loader, but Gatsby hides this a bit differently because it is a default package. This may or may not fix the problem but I'm not sure where to find and adjust the webpack config.

Update:

Custom widgets in netlifyCMS can sometimes struggle with stylesheets. So some have suggested to link it in the header of the component. I tried the following and that did not work either

...
return (
    <>
        <Helmet>
          <link rel="stylesheet" href="./RichTextEditor.css" />
        </Helmet>
        <MyCustomWidget ... />
    </>
)