解决方案:
将Popup的AllowsTransparency设置为True即可解决
<!-- QujiaoComboxItemStyle:下拉控件选中样式 -->
<Style TargetType="{x:Type ComboBoxItem}" x:Key="QujiaoComboBoxItemStyle">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ComboBoxItem}">
<Border x:Name="Bd">
<ContentPresenter/>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsSelected" Value="true">
<Setter Property="Background" TargetName="Bd" Value="#4e97ff"/>
</Trigger>
<Trigger Property="IsMouseOver" Value="true">
<Setter Property="Background" TargetName="Bd" Value="#4e97ff"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<!-- QujiaoComboxStyle:下拉控件样式 -->
<Style TargetType="{x:Type ComboBox}" x:Key="QujiaoComboBoxStyle">
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