C# WPF why does Window.Left = 0 appear between screen border and window?

Question

WPF

Visual Studio 2017, I create a new project (WPF Application), here is the main window class:

public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            Left = 0;
            Top = 0;
            Height = 1080;
            Width = 1920;
        }
    }

The screen size is 1920x1080, but when the program starts, there are some indents on the right, left and bottom. Where could they come from?

screenshot

Answer 1

It's not padding, it's the window border. The presence of a border and its thickness is set in the window properties or in styles, I don’t remember exactly, because it may be different in different OS versions.

Answer 2

This is the chrome of the window (WindowChrome), usually looks like a shadow around the window, is part of the window, on top of the client part. Usually the chrome size is 7px.
https://docs.microsoft.com/en-us/dotnet/api/system...
Chrome is disabled when the window is set to maximized (Maximized). And also, you can specify WindowStyle.None to the window, then the non-client part will be disabled.