How to remove the frame so that only the arrow ▼ remains? And you need to make the arrow white. Try this way
<ComboBox x:Name="comboBox" Width="16" Height="20" Margin="570,10,10,670" BorderBrush="{x:Null}" Background="{x:Null}" Foreground="Black" IsReadOnly="True"> <ComboBoxItem Content="Свернуть"/> <ComboBoxItem Content="Закрыть"/> </ComboBox> But this does not solve the problem. Thank you all in advance for your help!