直接拖出来的按钮是这样的，很丑。

我们只需要在XAML中给他添加几行代码就可以做成圆角形状。

<Button x:Name="button" Content="按钮" FontSize="40" BorderThickness="0" HorizontalAlignment="Left" Margin="25,58,0,0" VerticalAlignment="Top" Width="472" Height="200" Foreground="White">
	    <Button.Template>
	         <ControlTemplate TargetType="{x:Type Button}">
	             <Border BorderThickness="1" BorderBrush="Black" CornerRadius="30" Background="{TemplateBinding Background}">
	                 <ContentPresenter VerticalAlignment="Center" HorizontalAlignment="Center"/>
	             </Border>
	         </ControlTemplate>
	     </Button.Template>
</Button>

属性解析：
BorderThickness：边框的大小
BorderBrush：边框的颜色
CornerRadius：圆角的大小
Background：背景颜色"{TemplateBinding Background}"：这个就是使用上面<Button>的Background属性值作为他的值
<ContentPresenter VerticalAlignment="Center" HorizontalAlignment="Center"/>：文字垂直居中对齐

如图：

加个渐变色

<Button x:Name="button" Content="" FontSize="40" BorderThickness="0" HorizontalAlignment="Left" Margin="25,58,0,0" VerticalAlignment="Top" Width="472" Height="200" Foreground="White">
            <Button.Background>
                <LinearGradientBrush EndPoint="1,1" StartPoint="0,0">
                    <GradientStop Color="#FFC564B8" Offset="0"/>
                    <GradientStop Color="#FFF57A7A" Offset="1"/>
                </LinearGradientBrush>
            </Button.Background>
            <Button.Template>
                <ControlTemplate TargetType="{x:Type Button}">
                    <Border BorderThickness="1" CornerRadius="30" Background="{TemplateBinding Background}">
                        <ContentPresenter VerticalAlignment="Center" HorizontalAlignment="Center"/>
                    </Border>
                </ControlTemplate>
            </Button.Template>
        </Button>

如图：

一个简单好看的按钮就做好了