datepicker显示问题

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<c1:C1DatePicker Grid.Row="2" Grid.Column="3" Name="txtDate" Height="35" SelectedDateFormat="Short" AllowNull="True" DisplayMode="Month" Text="{Binding MeasureInfo.AppointmentTime}" Visibility="{Binding MeasureInfo.AppointmentType,Converter={StaticResource ValToVisible}}" Margin="0"/>

这个datepicker弹出的选择框样式有问题，帮忙看下是什么情况导致的。