<Style Selector="MenuItem.MainMenuHeader"><Setter Property="Foreground" Value="{DynamicResource MainMenuHeaderForeColor}"/><Style Selector="^:pointerover /template/ ContentPresenter#PART_HeaderPresenter"><Setter Property="Foreground" Value="{DynamicResource MainMenuHeaderHoverForeColor}"/></Style>
</Style>Avalonia MenuItem:pointerover setting foreground color
