progectone/App.axaml

<Application xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             x:Class="AvaloniaApplication4.App">
    <Application.Styles>
        <FluentTheme Mode="Light"/>
        <StyleInclude Source="avares://Avalonia.Themes.Default/DefaultTheme.xaml"/>
        <StyleInclude Source="avares://Avalonia.Themes.Default/Accents/BaseLight.xaml"/>
        <StyleInclude Source="avares://Avalonia.Controls.DataGrid/Themes/Default.xaml"/>
    </Application.Styles>
</Application>