I discover, the buttons and other "window" elements, they there are, but rendered grid is only limited size.
When I add Height="500" for example, Grid is not changed to this size. I implement move window, and if grid is moved with Height="500", is not moved, but only grid inside this grid. I create video for this problem and post it here, when I will have time.
Finally, problem described above is due my mainGrid has rows,
<Grid.RowDefinitions>
<RowDefinition Height="40" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Label Grid.Row="0" Content="TEXT" FontSize="16" FontWeight="Bold" Foreground="White"/>
<!-- ///////////////////////////////////////////////////////////////////////////////////////////////////////////////// GRID RESOURCES -->
<Grid.Resources>
<DataModel x:Name="dataModel" />
</Grid.Resources>
<!-- ///////////////////////////////////////////////////////////////////////////////////////////////////////////////// -->
<Grid x:Name="WindowContainer" >
</Grid>
if I add this code in WindowContainer
Grid is displayed in row 1 insitead row 0. And then grid inside WindowContainer grid is displayed full. Now question is, how to display grid in full window without add grid in to row or column?