Fix color of cluster labels in Mermaid flowcharts

[pawamoy]

See #3618

Without this change, a rule like color: #333 would be applied on clusters labels (.cluster span), making these difficult to read with the dark theme enabled.

I have other files that were modified, I think I should commit them as well (at least the ones already tracked)? Let me know.

 M material/base.html
 M material/overrides/main.html
 M package-lock.json
?? material/assets/javascripts/bundle.js
?? material/assets/javascripts/bundle.js.map
?? material/assets/javascripts/workers/search.js
?? material/assets/javascripts/workers/search.js.map
?? material/assets/stylesheets/main.css
?? material/assets/stylesheets/main.css.map
?? material/assets/stylesheets/palette.css
?? material/assets/stylesheets/palette.css.map
?? material/overrides/assets/javascripts/bundle.js
?? material/overrides/assets/javascripts/bundle.js.map
?? material/overrides/assets/stylesheets/main.css
?? material/overrides/assets/stylesheets/main.css.map

[squidfunk]

Thanks for the PR. Please go through the theme build process – it will remove all non-production files (which you currently see in your working copy). Please don't include the package-lock.json.

[squidfunk]

Could you please also share the Markdown that this PR fixes?

[pawamoy]

Example flowchart:

```mermaid
flowchart LR

client["client"]
load_balancer["load balancer"]
api1["API (replica 1)"]
api2["API (replica 2)"]
apin["API (replica N)"]

client --- load_balancer
subgraph openshift
    subgraph service
        api1 --- api2 --- apin
    end
    load_balancer --- service
end
```

flowchart LR

client["client"]
load_balancer["load balancer"]
api1["API (replica 1)"]
api2["API (replica 2)"]
apin["API (replica N)"]

client --- load_balancer
subgraph openshift
    subgraph service
        api1 --- api2 --- apin
    end
    load_balancer --- service
end

Before:

After:

[pawamoy]

I also have:

## fix-mermaid-subgraph-labels-color...origin/fix-mermaid-subgraph-labels-color
 M material/.icons/material/LICENSE
 D material/overrides/assets/javascripts/iconsearch_index.json

LICENSE seems to be CR/LF related. Not sure about the iconsearch_index.json deletion.
Let me know if I should rebase on master or resolve the conflict directly on GitHub.

[squidfunk]

Thanks! LGTM!