你可以达到这样的效果
通过将您的内容放置在 3x3 网格的中心(单元格 1,1),如下所示:
<Grid>
<Grid.Resources>
<Color x:Key="InnerColor">#FF000000</Color>
<Color x:Key="OuterColor">#FFFFFFFF</Color>
</Grid.Resources>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="20"/>
<ColumnDefinition />
<ColumnDefinition Width="20"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="20"/>
<RowDefinition/>
<RowDefinition Height="20"/>
</Grid.RowDefinitions>
<Rectangle Grid.Column="1" Grid.Row="0">
<Rectangle.Fill>
<LinearGradientBrush StartPoint="0,0" EndPoint="0,1">
<GradientStop Offset="0" Color="{StaticResource OuterColor}"/>
<GradientStop Offset="1" Color="{StaticResource InnerColor}"/>
</LinearGradientBrush>
</Rectangle.Fill>
</Rectangle>
<Rectangle Grid.Column="1" Grid.Row="2">
<Rectangle.Fill>
<LinearGradientBrush StartPoint="0,0" EndPoint="0,1">
<GradientStop Offset="0" Color="{StaticResource InnerColor}"/>
<GradientStop Offset="1" Color="{StaticResource OuterColor}"/>
</LinearGradientBrush>
</Rectangle.Fill>
</Rectangle>
<Rectangle Grid.Column="0" Grid.Row="1">
<Rectangle.Fill>
<LinearGradientBrush StartPoint="0,0" EndPoint="1,0">
<GradientStop Offset="0" Color="{StaticResource OuterColor}"/>
<GradientStop Offset="1" Color="{StaticResource InnerColor}"/>
</LinearGradientBrush>
</Rectangle.Fill>
</Rectangle>
<Rectangle Grid.Column="2" Grid.Row="1">
<Rectangle.Fill>
<LinearGradientBrush StartPoint="0,0" EndPoint="1,0">
<GradientStop Offset="0" Color="{StaticResource InnerColor}"/>
<GradientStop Offset="1" Color="{StaticResource OuterColor}"/>
</LinearGradientBrush>
</Rectangle.Fill>
</Rectangle>
<Rectangle Grid.Column="0" Grid.Row="0">
<Rectangle.Fill>
<RadialGradientBrush GradientOrigin="1,1" Center="1,1" RadiusX="1" RadiusY="1">
<GradientStop Offset="0" Color="{StaticResource InnerColor}"/>
<GradientStop Offset="1" Color="{StaticResource OuterColor}"/>
</RadialGradientBrush>
</Rectangle.Fill>
</Rectangle>
<Rectangle Grid.Column="2" Grid.Row="0">
<Rectangle.Fill>
<RadialGradientBrush GradientOrigin="0,1" Center="0,1" RadiusX="1" RadiusY="1">
<GradientStop Offset="0" Color="{StaticResource InnerColor}"/>
<GradientStop Offset="1" Color="{StaticResource OuterColor}"/>
</RadialGradientBrush>
</Rectangle.Fill>
</Rectangle>
<Rectangle Grid.Column="0" Grid.Row="2">
<Rectangle.Fill>
<RadialGradientBrush GradientOrigin="1,0" Center="1,0" RadiusX="1" RadiusY="1">
<GradientStop Offset="0" Color="{StaticResource InnerColor}"/>
<GradientStop Offset="1" Color="{StaticResource OuterColor}"/>
</RadialGradientBrush>
</Rectangle.Fill>
</Rectangle>
<Rectangle Grid.Column="2" Grid.Row="2">
<Rectangle.Fill>
<RadialGradientBrush GradientOrigin="0,0" Center="0,0" RadiusX="1" RadiusY="1">
<GradientStop Offset="0" Color="{StaticResource InnerColor}"/>
<GradientStop Offset="1" Color="{StaticResource OuterColor}"/>
</RadialGradientBrush>
</Rectangle.Fill>
</Rectangle>
</Grid>