Как сделать непрозрачный контрол на прозрачном бордере?

<Window x:Class="DELETE_DELETE.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" MinHeight="200" MinWidth="415" WindowStyle="None" AllowsTransparency="True" Background="{x:Null}"
        TextOptions.TextFormattingMode="Display" mc:Ignorable="d" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" d:DesignHeight="200" d:DesignWidth="415" SizeToContent="WidthAndHeight">
    <Grid>
        <Border BorderBrush="#6943B5E5" BorderThickness="1" Name="border1" MouseDown="border1_MouseDown" Background="#453978C1" CornerRadius="25">
            <Grid Name="grid1">
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="139*" />
                    <ColumnDefinition Width="136" />
                    <ColumnDefinition Width="145*" />
                </Grid.ColumnDefinitions>
                <TextBox Height="23" Margin="17,30,12,0" Name="textBox1" VerticalAlignment="Top" Grid.ColumnSpan="3" />
                <Button Content="Закрыть" Height="23" Margin="0,0,0,14" Name="btnClose" VerticalAlignment="Bottom" Grid.Column="1" Click="btnClose_Click" />
            </Grid>
        </Border>
    </Grid>
</Window>