For security reasons, browsers impose limitations on pages that you open locally through your filesystem. You have to use a local webserver. There are many options for setting one up permanently, but if you have Python 3 installed a very simple temporary option is to run python3 -m http.server inside the directory. Tested on Linux; should work as-is on Mac; on Windows you may need to add the Python executable to your path or use the full path to it.