Fix light and dark theming

[raphaelsalaja]

Problem

There is an issue regarding some UI elements not having their respective dark and light mode variants. This appears due to two reasons.

1. Lack of Defined Colour

Text(title).font(.title3).fontDesign(.rounded).fontWeight(.bold)

2. Explicit Colours

.background(Color(.white))

Additional Context

Can be prevented by defining a base theme, or by colours with in-built variants.