Using body[data-theme] instead of html[data-theme] breaks using theme switcher

[AliveDevil]

Describe the bug

A theme switcher component sets data-theme on html-element, not on html.body, as html attributes aren't inherited, Tabs break when using html.data-theme.

Reproduce the bug

1. Create project with sphinx-rtd, sphinx-tabs and sphinx-rtd-dark-mode
2. Create tab
3. Switch theme

List your environment

No response

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