（WPF初学者）Button和Gird相互覆盖怎么解决

Question

我在Grid下设置了一个渐变的Grid.Background和一个普通的Button按钮，但是，加了按钮之后背景就没有了，这时怎么回事？

<Window x:Class="Buttin._1.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:Buttin._1"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Grid.Background>
            <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                <GradientStop Color="Red" Offset="0"/>
                <GradientStop Color="Yellow" Offset="0.6"/>
                <GradientStop Color="AliceBlue" Offset="1"/>
            </LinearGradientBrush>

        </Grid.Background>
        <Button>
            <Button.Content >
                <StackPanel Orientation="Vertical" Height="240">
                    <Image Source="a.jpg" Width="150" Height="200"/>
                    <TextBox Text="Smile" VerticalAlignment="Center" HorizontalAlignment="Center" FontSize="30"/>
                </StackPanel>
            </Button.Content>
        </Button>
    </Grid>
</Window>

Answer 1

按钮太大了，设置一下按钮的width和height