avalonia_first_practic/aval_fp/App.axaml

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

    <Application.Styles>
        <FluentTheme />
		<!--<StyleInclude Source="/Styles/ElementStyles.axaml"></StyleInclude>-->
		<StyleInclude Source="/Styles/ElementStyles.axaml"></StyleInclude>
    </Application.Styles>
</Application>