- Modifed the form to have two color fields (one for dark and one for light theme).
- The colors are stored  in this form"#ffffff,#000000". Where the first one is for light theme and the other for dark theme.
- Then the custom.css consumes the values and performs a split(defined in custom_filters.py) on the color string to get the two colors.
- Those colors then are defined in css variables and consumed by the elements that need them.
- The css variables change base on the current theme (for dark values to be applied it is expected that the body tag has `data-theme="dark"`)

- Insure backward compatibility with previous theme color settings.

- In the new implementation it considers if there was previous color settings. If so it applies them to dark theme colors too.