Semi.Avalonia/src/Semi.Avalonia.Demo/MainWindow.axaml

<Window 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"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        x:Class="Semi.Avalonia.Demo.MainWindow"
        Title="Semi.Demo">
    <StackPanel>
        <Button>Primary</Button>
        <Button>Secondary</Button>
    </StackPanel>
</Window>