But when you press the button, you're running Python code... how does that work? Toga uses `PyScript <https://pyscript.net>`__ to provide a Python interpreter in the browser. Briefcase packages your app's code as wheels that PyScript can load in the browser. When the page is loaded, the application code runs in the browser, building the UI using the browser DOM. When you click a button, that button runs the event handling code in the browser.