Semi.Avalonia/src/Semi.Demo/App.axaml

<Application xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             x:Class="Semi.Demo.App">
    <Application.Styles>
        
    </Application.Styles>
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceInclude Source="avares://Avalonia.Themes.Semi/Themes/DarkTheme.axaml"/>
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
</Application>