Sure, you don't develop something on the side for an existing IDE which treats your content as remote and potentially insecure, prohibiting access to DOM and other useful APIs like embedding editors. If you are building an end product for particular developers you want to be in the control of final developer experience, you don't want to deal with limitations of iframes because your content is not remote, you want to change styles, access DOM and have good integration with editors. Consider new Arduino IDE, they have to provide similar UX as old IDE for smooth transition. It requires disabling many features by default and complete restyling and rebranding. There is no way to do it with VS Code apis.