Option to change the appearance of the application with the theme file.

[artem-rodionov]

Feature Description

It is suggested to create a theme file, which will list the dependencies for changes in the design. For example, as a file settings in vs code.
Changing the design means things like changing the icons (the path to the new icon), adding new colors (I want to add pure white and pure black because through ColorScheme.FromSeed, as far as I know, does not do this), changing various widget characteristics.
At the moment, it is assumed that the design change will be made using a script that takes information from the theme file.

I would l like to hear feedback on whether such functionality is needed? If so, what other suggestions do you have, especially regarding the implementation of the change itself (a separate script or, for example, integrating it into the workflow)?
Thank you!

Rationale

In my opinion, it would be nice to have additional customization functionality that can be performed automatically.

Mockup

The view of the login page modified by the script.

Additional Context

No response