Without knowing what you changed, I can't tell you where you went wrong. Please answer all of the questions I ask.
Do you get any errors in the server logs or in your browser console when you attempt to access the page?
Trying to reimplement what is used in plugin-quickstart in theme-quickstart was unsuccessful (white page as well).
Yes, plugin quick start is where you want to look if you're adding new pages. https://github.com/NodeBB/nodebb-plugin-quickstart/blob/104b739ed8f8a82b36f92fa4b680238ebb1d8306/library.js#L19