Flowchart: Not able to set style for dotted/Thick links through themes or themeCSS

[sulabh-msft]

Describe the bug
FlowChart: Not able to set style the styles for dotted/think links through themes or by specifying styles though themeCSS initialize option

Mermaid version 8.2.3

Dotted link

graph LR;
   A-.->B;

Thick link

graph LR
   A ==> B

To Reproduce

1. Go to the Mermaid editor
   Code:

graph TD;
A[Christmas] -.->|Get money| B(Go shopping)

Theme: default
or Go to the Mermaid Editor default theme

Now change the theme to dark
Theme: dark

Mermaid editor dark theme

Observe the color of dotted link. It is not changing across themes. This is resulting in issue where back-ground is also dark ( dark theme)

Expected behavior
The style for dotted/thick links IMO we should have different style for these links in dark theme We should also have it exposed as a separate css class name to that it is customizable through themeCSS option.

Desktop (please complete the following information):

• OS: [Window]
• Browser [chrome]
• Version 76.0.3809.132

Additional context
Looks like the styles are hard coded for dotted/thick links.

Snippet
/// https://github.com/knsv/mermaid/blob/master/src/diagrams/flowchart/flowRenderer.js (line: 193)

    if (typeof edge.style !== 'undefined') {
      edge.style.forEach(function(s) {
        style = style + s + ';';
      });
    } else {
      switch (edge.stroke) {
        case 'normal':
          style = 'fill:none';
          if (typeof defaultStyle !== 'undefined') {
            style = defaultStyle;
          }
          break;
        case 'dotted':
         // ISSUE:  HARD CODED STYLE for dottted
          style = 'stroke: #333; fill:none;stroke-width:2px;stroke-dasharray:3;';  
          break;
        case 'thick':
         // ISSUE:  HARD CODED STYLE for thick
          style = 'stroke: #333; stroke-width: 3.5px;fill:none';   
          break;
      }
    }

[knsv]

@sulabh-msft Thanks for your the issues you have reported on mermaid. They are all good ideas, valid and excellently reported. I have been looking at UML diagrams during autumn but will give flowcharts more focus now.