How to create WPF responsive menu bar (full-width)

I have a WPF application which has a Full screen with WindowState="Maximized" enabled but I can not doc the Menu to display full screen. I removed the width property from the window but still displaying the menu in small part of the screen.

How can I make the Menu to behave responsive?

<Window x:Class="UMAp.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:UBrochure"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525" WindowState="Maximized">
    <Grid Background="Gray" >
        <Menu x:Name="menu" HorizontalAlignment="Left" Height="28" VerticalAlignment="Top" >
            <Button Content="Edit" BorderThickness="0" Background="#FFF0F0F0"/>
            <Button BorderThickness="0" Content="  Templates" Background="#FFF0F0F0"/>
        </Menu>
        <Grid Background="#FF51514B" HorizontalAlignment="Left" Height="291" Margin="0,28,0,0" VerticalAlignment="Top" Width="134"/>
    </Grid>
</Window>