Why does the dropdown arrow disappears when I try to use the following code? Is there any other method which I can round out the corners of the combobox? Thanks!

Code:
<ControlTemplate x:Key="ComboBoxTemplate" TargetType="{x:Type ComboBox}">
    <Grid>
        <Border x:Name="border" Background="White" BorderBrush="#FFFFC934" BorderThickness="2" CornerRadius="10,10,10,10" Width="Auto" Height="Auto">
        </Border>
    </Grid>
</ControlTemplate>