RxUiHostView.xaml

<UserControl x:Class="Trader.Client.Views.RxUiHostView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:views="clr-namespace:Trader.Client.Views"
             xmlns:reactiveUi1="http://reactiveui.net"
             xmlns:views1="clr-namespace:Trader.Client.Views"
             mc:Ignorable="d" 
             x:Name="ContentHolder"
              d:DataContext="{d:DesignInstance views:RxUiHostViewModel, IsDesignTimeCreatable=False}"
             d:DesignHeight="300" d:DesignWidth="300">

    <views1:RxUiHostView Content="{Binding Content}"
                            HorizontalContentAlignment="Stretch"
                            VerticalContentAlignment="Stretch"/>

</UserControl>