Feature request: Add option to provide a wrapper html page (with additional css or js files included)

I'm using this extension to display a live preview of html snippets, that will later be included into a larger page context in a CMS (in my case Moodle). In order to get an accurate preview, I need to provide a wrapper html page, which includes the required css files (and even one js file which changes the content dynamically after that page load).

It would be great if it was possible to define the wrapper file, either in the workspace-settings or even better through a magic comment in the html snippet, e.g. <!-- wrapper:./preview.html -->. The wrapper would need to define where the snippet is to be added, e.g. with a {{ content }} tag.