我的用法
用Rectangle作背景（好处是可以设置渐变色），然后用Grid分段，在其中一个格子里填充Button，然后在Button里添加一个背景透明的png图片
出现问题
虽然按钮图片的背景色是透明的，但是按钮区域仍然会有一个半透明的阴影，尝试使用纯文字也一样。如下图：
官方用例的解决方案
官方Windows-universal-samples-master的用例里，汉堡菜单使用的是ToggleButton，然后使用了自定义样式ToggleButton Style="{StaticResource SymbolButton}"
Style代码
<Style x:Key="SymbolButton" TargetType="ToggleButton">
<Setter Property="Background" Value="{ThemeResource ToggleButtonBackgroundThemeBrush}"/>
<Setter Property="Foreground" Value="{ThemeResource ToggleButtonForegroundThemeBrush}"/>
<Setter Property="BorderBrush" Value="{ThemeResource ToggleButtonBorderThemeBrush}"/>
<Setter Property="BorderThickness" Value="{ThemeResource ToggleButtonBorderThemeThickness}"/>
<Setter Property="Padding" Value="12,4,12,5"/>
<Setter Property="HorizontalAlignment" Value="Left"/>
<Setter Property="VerticalAlignment" Value="Center"/>
<Setter Property="FontFamily" Value="{ThemeResource ContentControlThemeFontFamily}"/>
<Setter Property="FontWeight" Value="SemiBold"/>
<Setter Property="FontSize" Value="{ThemeResource ControlContentThemeFontSize}"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ToggleButton">
<Grid>
<VisualStateManager.VisualStateGroups>
<VisualStateGroup x:Name="CommonStates">
<VisualState x:Name="Normal"/>
<VisualState x:Name="PointerOver">
<Storyboard>
</Storyboard>
</VisualState>
<VisualState x:Name="Pressed">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentPresenter">
<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonCheckedPressedBackgroundThemeBrush}"/>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="Disabled">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentPresenter">
<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonDisabledForegroundThemeBrush}"/>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="Checked">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentPresenter">
<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonCheckedBackgroundThemeBrush}"/>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="CheckedPointerOver">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentPresenter">
<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonCheckedPointerOverBackgroundThemeBrush}"/>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="CheckedPressed">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentPresenter">
<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonCheckedPressedBackgroundThemeBrush}"/>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="CheckedDisabled">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentPresenter">
<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonCheckedDisabledForegroundThemeBrush}"/>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="Indeterminate"/>
<VisualState x:Name="IndeterminatePointerOver">
</VisualState>
<VisualState x:Name="IndeterminatePressed">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentPresenter">
<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonPressedForegroundThemeBrush}"/>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="IndeterminateDisabled">
<Storyboard>
<ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentPresenter">
<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ToggleButtonDisabledForegroundThemeBrush}"/>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
</VisualStateGroup>
<VisualStateGroup x:Name="FocusStates">
<VisualState x:Name="Focused">
<Storyboard>
<DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="FocusVisualWhite"/>
<DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="FocusVisualBlack"/>
</Storyboard>
</VisualState>
<VisualState x:Name="Unfocused"/>
<VisualState x:Name="PointerFocused"/>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<ContentPresenter x:Name="ContentPresenter" AutomationProperties.AccessibilityView="Raw" ContentTemplate="{TemplateBinding ContentTemplate}" ContentTransitions="{TemplateBinding ContentTransitions}" Content="{TemplateBinding Content}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
<Rectangle x:Name="FocusVisualWhite" IsHitTestVisible="False" Opacity="0" StrokeDashOffset="1.5" StrokeEndLineCap="Square" Stroke="{ThemeResource FocusVisualWhiteStrokeThemeBrush}" StrokeDashArray="1,1"/>
<Rectangle x:Name="FocusVisualBlack" IsHitTestVisible="False" Opacity="0" StrokeDashOffset="0.5" StrokeEndLineCap="Square" Stroke="{ThemeResource FocusVisualBlackStrokeThemeBrush}" StrokeDashArray="1,1"/>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
后续研究
这和之前我用的模式差不多，但是之前是样式大变样，所以必须要自定义样式。
但是这样有一个蔽端，按钮的状态减少了很多。需要对Button样式进行完整的自定义，主要应该是<VisualStateManager.VisualStateGroups>里的内容。