Fix dark mode if theme is not set

[billmn]

If theme is not set in localStorage (e.g. a user did not choose the theme to use), fallback to the theme used by filament (if OS uses dark mode, there is a dark class in the body)

[leandrocfe]

If theme is not set in localStorage (e.g. a user did not choose the theme to use), fallback to the theme used by filament (if OS uses dark mode, there is a dark class in the body)

I'm currently working on some enhancements and I'll change it to something like this:

theme: document.querySelector('html').matches('.dark') ? 'dark' : 'light',

I believe that it will work better. Thank you!

[billmn]

Thank you!