refactor(theme): use relative units for dropdowns

[dr-itz]

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Documentation.
Examples.
Dashboards Demo.
Playwright report.

Coverage Reports:

• charts-ng
• dashboards-ng
• element-ng
• element-translate-ng
• maps-ng
• native-charts-ng

[gemini-code-assist]

Code Review

This pull request introduces a new menu example and updates dropdown styles to use dynamic sizing and the :is() selector. Feedback focuses on restoring the !default flag to a theme variable to allow for overrides, removing unsupported text content from a menu divider, and adhering to the style guide by importing standalone components instead of an NgModule.

[spliffone]

With the current approach the si-select template is limited to one line, do we have the changes to fix this behaviour too?

[dr-itz]

With the current approach the si-select template is limited to one line, do we have the changes to fix this behaviour too?

done

[dr-itz]

With the current approach the si-select template is limited to one line, do we have the changes to fix this behaviour too?

done

nope, too much is broken

[dr-itz]

With the current approach the si-select template is limited to one line, do we have the changes to fix this behaviour too?

done

nope, too much is broken

reverted, too much for this PR and out of scope anyway