ConstWorkbookElement and WorksheetElement render this at their roots. Render it yourself only when you
build your own shell around them and its chrome sits outside their roots: then that shell is the theme
root. Set data-sxl-theme-mode on the root element alongside the class.
const scopeClass = createThemeScopeClass('shell', useId());
<div className={scopeClass} data-sxl-theme-mode="dark">
<ThemeRootStyles scopeClass={scopeClass} />
…
</div>
The stylesheets that make an element a self-contained themed instance: the neutral token defaults for the
app,gridandheadersurfaces, the spreadsheet system colors (--sxl-sys-color-*) resolved against those surfaces, and the host's ThemeRootStylesProps.tokens, all scoped toscopeClass.