DataContext in XAML

MainWindow.xaml

<Window x:Class="WPFUI.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:viewModels="clr-namespace:SOSCSRPG.ViewModels;assembly=SOSCSRPG.ViewModels"
        d:DataContext="{d:DesignInstance viewModels:GameSession}"
        mc:Ignorable="d"
        FontSize="11pt"
        Title="{Binding GameDetails.Title}" Height="768" Width="1024"
        KeyDown="MainWindow_OnKeyDown"
        Closing="MainWindow_OnClosing">