Rework website colors

[ctmbl]

Context

The website supports two themes:

• light
• dark

therefore every content should support both.

Problem

However currently sometimes hardcoded colored are used sometimes its configurable ones (see CSS file and the config file).
Also sometimes a color is used in a non-intended way, for example a background color is used as a font-color, which could result in invisible words for some config.

Tasks

• list hardcoded color
• change hardcoded colors to configurable
• check that every light color has its dark counter-part and vice versa
• list color usage and verify that an appropriate color is used
• test in light mode
• test in dark mode