Edit App.xaml file:

<Application ...
  xmlns:themes="clr-namespace:Material.Styles.Themes;assembly=Material.Styles"
  ...>
  <Application.Styles>
    <themes:MaterialTheme BaseTheme="Dark" PrimaryColor="Purple" SecondaryColor="Lime" />
  </Application.Styles>
</Application>

Installing additional packages:

All styles will be included automatically if you using MaterialTheme

• If you want to use DataGrid control, add Material.Avalonia.DataGrid package:

  dotnet add package Material.Avalonia.DataGrid
  

  

• If you want to use TreeDataGrid control, add Material.Avalonia.TreeDataGrid package:

  dotnet add package Material.Avalonia.TreeDataGrid
  

  

• If you want to use dialogs provided from Material.Avalonia, add Material.Avalonia.Dialogs package:

  dotnet add package Material.Avalonia.Dialogs
  

  

Done! Now your app is styled! You can use the Demo app to view how different styles look.
Every control has the ShowMeTheXaml button in the right bottom corner which will show you a markup needed to recreate it.