As an AI language model, I can help you with the process of creating a simple 3D Mario game using JavaScript enclosed in script tags within a single HTML file. However, please note that creating a full-fledged 3D game requires advanced programming skills and a significant amount of code, which cannot be provided entirely here. I will guide you through the basic structure and steps to get started with creating a simple game. Here's an example of how you can begin:
This is a basic template that sets up the HTML structure, CSS styling, and JavaScript code for handling game logic. You can expand on this foundation by adding functions and implementing the game mechanics, such as player movement, collision detection, and rendering 3D objects. Remember, creating a full 3D game requires advanced knowledge of graphics programming, libraries, or frameworks. Feel free to consult game development resources and tutorials for more detailed guidance.