Implement Dark Mode

[Isax03]

Feature Request: Dark Mode

Is your feature request related to a problem? Please describe.
For users who work late at night or simply prefer a darker interface, the current light-themed interface can cause eye strain and discomfort. A dark mode option would be helpful to reduce eye fatigue in low-light environments.

Describe the solution you'd like
I would like to request the implementation of a dark mode for the invoice/receipt generator. This option would allow users to toggle between the light and dark themes based on their preferences, improving the user experience, especially in dark settings.

Describe alternatives you've considered
Currently, users have to rely on third-party extensions or browser settings to invert colors or reduce brightness, but a built-in dark mode would be a more elegant and accessible solution.

Additional context
Dark mode is becoming a standard feature across modern applications and websites. It offers better usability in low-light environments, enhances focus, and is generally more comfortable for users who prefer it.

[Isax03]

I am available to implement that during hacktoberfest

[ypratham]

@Isax03 I'll assign this issue to you with appropriate labels.