Wrong background color on mate panel for "mixed" themes

[Tichy]

Mate version: 1.28.2

I installed the themes using the install.sh script. The installation ended well without errors.

The issue that I have is that the mate panel mate is colored in white background with white text.

It should be dark with white text

I was able to find the style to fix inside the generated gtk3 gtk.css file:

Example for Vimix-doder at line 7214

#PanelPlug,
PanelToplevel.background {
  background-color: #292B2E;
  color: rgba(0, 0, 0, 0.6);
  font-weight: 500;
}

But I don't know how to fix it inside the templates in _sass to obtain the fixed css files when generating them with the install.sh script, otherwise I would have made a branch and a pull request with the fix.