MainWindow.xaml

<Window x:Class="RngHelper.MainWindow"
        x:Name="RngWindow"
        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"
        xmlns:local="clr-namespace:RngHelper"
        mc:Ignorable="d"        
    Title="RngHelper" Height="75" Width="75" ResizeMode="CanResize" Topmost="True" WindowStyle="None" MouseDown="Window_MouseDown">
    <Grid Background="{Binding BackgroundColor}">
        <Grid.RowDefinitions>
            <RowDefinition Height="*"></RowDefinition>
        </Grid.RowDefinitions>
        <TextBlock x:Name="txtBox" Grid.Row="0" TextAlignment="Center" Padding="5" VerticalAlignment="Center" FontWeight="Bold" Text="{Binding Random}" Background="{Binding BackgroundColor}"></TextBlock>
    </Grid>
</Window>