AvaloniaProject/AvaloniaApplication4/App.axaml

<Application xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             x:Class="AvaloniaApplication4.App"
             xmlns:local="using:AvaloniaApplication4"
             RequestedThemeVariant="Light">
             <!-- "Default" ThemeVariant follows system theme variant. "Dark" or "Light" are other available options. -->

    <Application.DataTemplates>
        <local:ViewLocator/>
    </Application.DataTemplates>

	<Application.Styles>
		<FluentTheme />
		<StyleInclude Source="/Styles1.axaml"/>
		<StyleInclude Source="avares://Avalonia.Controls.DataGrid/Themes/Fluent.xaml"/>
	</Application.Styles>
	<Application.Resources>
		<FontFamily x:Key="MontserratRegular">avares://AvaloniaApplication1/Assets/Fonts/Montserrat-Regular.ttf#Montserrat</FontFamily>
		<FontFamily x:Key="MontserratBold">avares://AvaloniaApplication1/Assets/Fonts/Montserrat-Bold.ttf#Montserrat</FontFamily>
		<FontFamily x:Key="MontserratSemiBold">avares://AvaloniaApplication1/Assets/Fonts/Montserrat-SemiBold.ttf#Montserrat</FontFamily>
	</Application.Resources>
</Application>