Docs: Fix xarray Dataset double-rendering in MkDocs

[Copilot]

In the rendered docs, plan.open_dataset() output displayed both the plain-text fallback and the interactive HTML repr simultaneously (before, below):

Root cause: xarray embeds a <style> block in its HTML repr to hide .xr-text-repr-fallback and show .xr-wrap. The MkDocs Material theme's <pre> rules have higher specificity than xarray's bare .xr-text-repr-fallback { display: none }, so the text fallback leaks through. The xr-wrap div shows correctly because xarray uses !important there, but not on the fallback.

Fix — docs/stylesheets/extra.css:

• Add .md-content .xr-text-repr-fallback { display: none !important } to win the specificity battle against the Material theme's pre rules
• Add .md-content .xr-wrap { display: block !important } as an explicit guard
• Map --xr-* color variables to MkDocs Material equivalents (--md-default-fg-color, --md-code-bg-color, etc.) — xarray's CSS expects Jupyter's --jp-* variables which are absent in MkDocs, so without this the widget renders with incorrect colors in both light and dark mode

After the fix, only the interactive collapsible xarray widget is shown, matching the Jupyter notebook experience.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Docs: somthing wrong with rendering of xarray output</issue_title>
<issue_description>Task: Improve xarray Dataset rendering. Preferably how it looks in jupyter notebook

ds = plan.open_dataset(0)
ds

is outputing this. It is showing both print(ds) and a garbled html version of the xarray output

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Docs: somthing wrong with rendering of xarray output #99

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