Iam using CefSharp\'s SchemeHandler in order to grab resources from my C# project like .css, .js or .png files using a custom url for
If you simply need to return a string, then you can use ResourceHandler.FromString(html, mimeType). For this you just need to implement the ISchemeHandlerFactory.
https://github.com/cefsharp/CefSharp/blob/cefsharp/47/CefSharp/ResourceHandler.cs#L98
Example reading from a file https://github.com/cefsharp/CefSharp/blob/cefsharp/47/CefSharp.Example/CefSharpSchemeHandlerFactory.cs#L17 which can be translated to reading from a string quite simply.