MercuryConverter/UI/Dialogs/DataOpen.axaml

<UserControl xmlns="https://github.com/avaloniaui"
        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:MercuryConverter.UI.Dialogs"
        xmlns:progRing="clr-namespace:AvaloniaProgressRing;assembly=AvaloniaProgressRing"
        x:Class="MercuryConverter.UI.Dialogs.DataOpen"
>
    <StackPanel Margin="12">
        <TextBlock Text="Select your data folder..."/>
        <progRing:ProgressRing Foreground="{DynamicResource SystemBaseMediumColor}"
            Width="36" 
            Height="36"
            IsActive="True"
            HorizontalAlignment="Center"
            Margin="0,15,0,0"/>
    </StackPanel>

</UserControl>