WPopupPlayer.xaml

<Window x:Class="CustomToolbox.WPopupPlayer"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d"
        Title="WPopupPlayer"
        MinHeight="255"
        Height="480" 
        MinWidth="426"
        Width="854"
        Closing="WPopupPlayer_Closing"
        Loaded="WPopupPlayer_Loaded">
    <Grid Background="#FFE5E5E5">
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <WindowsFormsHost x:Name="WFHContainer"
                          Grid.Row="0" 
                          MinHeight="240"
                          Height="Auto"
                          MinWidth="426"
                          Width="Auto"
                          Margin="0,0,0,0">
        </WindowsFormsHost>
    </Grid>
</Window>