Install-Package MahApps.Metro
open up MainWindow.xaml or Shell View (View that contains your first window)
add this attribute inside the opening Window tag. (It’s how you
reference other namespaces in XAML):
xmlns:Controls="clr-namespace:MahApps.Metro.Controls;assembly=MahApps.Metro"
or
xmlns:Controls="http://metro.mahapps.com/winfx/xaml/controls"
change <Window ... tag to <Controls:MetroWindow ... (remember to change the closing tag too!)
Remove window inheritance from code behind file.
All of MahApp.Metro’s resources are contained within separate resource dictionaries. In order for most of the controls to adopt the MahApps.Metro theme, you will need to add the ResourceDictionaries to your App.xaml.
<Application x:Class="WpfApplication.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
StartupUri="MainWindow.xaml">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<!-- MahApps.Metro resource dictionaries. Make sure that all file names are Case Sensitive! -->
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Fonts.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Colors.xaml" />
<!-- Accent and AppTheme setting -->
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Accents/Blue.xaml" />
<ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Accents/BaseLight.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
</Application>