[Feature Request] Dark / Light Theme switch

[PerfectlyFineCode]

I would love a light / dark switch in the preview to switch between the themes instead of having to explicitly define the theme in design by:

<Design.DesignStyle>
    <Style Selector="Window">
        <Setter Property="RequestedThemeVariant" Value="Dark" />
    </Style>
</Design.DesignStyle>

Example of how it could look