Capacitor app with dark mode

[DuncanTLaw]

I am coding using Angular Ionic with Capacitor. I would like to make a toggle for dark mode:

Light | Dark | Auto

where light or dark is the appearance of the PWA and 'Auto' follows system dark/light mode.

I have tried removing the CSS rule @media (prefers-color-scheme: dark) then dynamically adding class = "dark" which does work, however when the system OS toggles back to light mode the app goes back to light mode. How can I make sure that the theme is retained? I have added window.addEvenetListener('change', (ev) => { this.dark = ev } to listen to the change event.