ryujinx/src/Ryujinx/App.axaml

<Application
    x:Class="Ryujinx.Ava.App"
    xmlns="https://github.com/avaloniaui"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:sty="using:FluentAvalonia.Styling">
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <MergeResourceInclude Source="/Assets/Styles/Themes.xaml"/>
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
    <Application.Styles>
        <sty:FluentAvaloniaTheme PreferSystemTheme="False" />
        <StyleInclude Source="/Assets/Styles/Styles.xaml" />
    </Application.Styles>
</Application>