Simplify theming

[knsv]

As an integrator integrating mermaid to a site or a too,l theming might is timeconsuming. There to many options and parameters to change making it difficult.

Instead of overriding the css there should be a base set of theming parameters to set that are easy to understand without going deep into the svg markup of a generated mermaid svg. These parameters should then generate the theme dynamically.

• The less colors to customize the better
• The easier it is to extract all color-related CSS properties the better
• Add sample mermaid diagrams that used all colors, make rendering test with supported themes for those diagrams
• Add those sample diagrams to the live editor for easy access