[Blazor] Some of the default UI styling is not accessible in dark mode

[MackinnonBuck]

There are cases where the styling of some of Blazor's built-in UI elements gets adversely affected by global dark mode styling.

Some examples:

1. The server reconnect UI:
   

2. The "Yellow bar":
   

We should consider styling these elements in ways that don't inherit from other styles defined in the app.

[javiercn]

Looked at the four pieces of UI we produce:

• Blazor Error UI (yellow bar) needs color-scheme: light only on the template to avoid issues with auto dark mode.
• Blazor Loading animation: Seems fine, no changes needed.
• Error boundary UI: It's fine, no changes needed.
• Blazor Server reconnect UI. From what was described in this issue, there were problems when styles where changes. To avoid that, I've put all the content inside a shadow root to avoid accidental styling.
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  • Contrast in auto dark mode is not great, but the text is clear.