一般创建的 Window 窗口默认布局如下:

<Window x:Class="WPFDemo.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:local="clr-namespace:WPFDemo"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        
    </Grid>
</Window>

运行效果如下:

将window的 WindowStyle 属性设置为 None, 则可去掉顶部的菜单条.

<Window x:Class="WPFDemo.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:local="clr-namespace:WPFDemo"
        mc:Ignorable="d"
        WindowStyle="None"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        
    </Grid>
</Window>

效果如下:

现在给 Grid外部添加一个 Border 设置圆角和背景色, 同时设置Window的 Background="Transparent"AllowsTransparency="True"

<Window x:Class="WPFDemo.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:local="clr-namespace:WPFDemo"
        mc:Ignorable="d"
        WindowStyle="None"
        Background="Transparent"
        AllowsTransparency="True"
        Title="MainWindow" Height="450" Width="800">
    <Border CornerRadius="10" Background="Red">
        <Grid>

        </Grid>
    </Border>
    
</Window>

运行效果如下:

上图即为圆角窗口, 四角黑色为截图软件导致.