1.
<Grid Background="Transparent" >
2.
<Border Grid.ColumnSpan="2" Grid.RowSpan="3" BorderThickness="1" CornerRadius="25" BorderBrush="Black" HorizontalAlignment="Left" Height="599" VerticalAlignment="Top" Width="359" Background="#FF1AF1E8">
3.
<Grid HorizontalAlignment="Left" Height="599" VerticalAlignment="Top" Width="359" Margin="0" >

1、用Border.Clip
2、按钮应用这个圆角：
<CornerRadius x:Key="MyCorner">
<CornerRadius.TopLeft>0</CornerRadius.TopLeft>
<CornerRadius.TopRight>10</CornerRadius.TopRight>
<CornerRadius.BottomLeft>0</CornerRadius.BottomLeft>
<CornerRadius.BottomRight>0</CornerRadius.BottomRight>
</CornerRadius>

没看懂

修改按钮原模板