message: Light/dark mode switch to Preferences - UI part (win)
diff: <TabItem Header="General">
  <ScrollViewer>
  <StackPanel Margin="24 32 24 48">
  - <TextBlock Style="{DynamicResource Toggl.TitleText}" Text="Set up shortcuts" />
  + <TextBlock Style="{DynamicResource Toggl.TitleText}" Text="Light/Dark mode" />
  + <ComboBox Margin="0 6 0 0" Width="360">
  + <ComboBoxItem>Use my Windows mode</ComboBoxItem>
  + <ComboBoxItem>Light</ComboBoxItem>
  + <ComboBoxItem>Dark</ComboBoxItem>
  + </ComboBox>
  + <TextBlock Margin="0 32 0 0" Style="{DynamicResource Toggl.TitleText}" Text="Set up shortcuts" />
  <Grid Margin="0 16 0 0" HorizontalAlignment="Left">
  <Grid.RowDefinitions>
  <RowDefinition />
  