sadikurahman321-cell/study.box ? reverse-engineered prompt

Build me a simple study box web app for helping me review notes and quiz myself.

I want a clean site with a place to manage study items, a place to store the main content, and a play mode where I can go through the material like flashcards or prompts and answers. It should feel lightweight and easy to use, with a nice layout and clear buttons for switching between the main views. If you need to, look up current docs online to make sure the browser APIs and any small JavaScript details are done the right way.

Please make it work well in a browser, keep the design simple and readable, and make sure the data can be loaded and saved in a sensible way so I do not lose my study set. I want the whole thing to feel polished enough that I can open it and immediately start studying without any setup.