Я изменил свой предыдущий пользовательский стиль следующим образом:
<Window.Resources>
<Style x:Key="CustomCalendar" TargetType="{x:Type Calendar}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Calendar}">
<Viewbox Height="300" Width="300" >
<CalendarItem x:Name="PART_CalendarItem"
Background="{TemplateBinding Background}"
BorderBrush="{TemplateBinding BorderBrush}"
BorderThickness="{TemplateBinding BorderThickness}" FontStretch="Expanded">
</CalendarItem>
</Viewbox>
</ControlTemplate>
</Setter.Value>
</Setter>
<Setter Property="CalendarDayButtonStyle">
<Setter.Value>
<Style TargetType="{x:Type CalendarDayButton}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type CalendarDayButton}">
<Grid>
<VisualStateManager.VisualStateGroups>
<VisualStateGroup x:Name="CommonStates">
<VisualStateGroup.Transitions>
<VisualTransition GeneratedDuration="0:0:0.1"/>
</VisualStateGroup.Transitions>
<VisualState x:Name="Normal"/>
<VisualState x:Name="MouseOver">
<Storyboard>
<DoubleAnimation Duration="0" To="0.5" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="HighlightBackground"/>
</Storyboard>
</VisualState>
<VisualState x:Name="Pressed">
<Storyboard>
<DoubleAnimation Duration="0" To="0.5" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="HighlightBackground"/>
</Storyboard>
</VisualState>
<VisualState x:Name="Disabled">
<Storyboard>
<DoubleAnimation Duration="0" To="0" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="HighlightBackground"/>
<DoubleAnimation Duration="0" To=".35" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="NormalText"/>
</Storyboard>
</VisualState>
</VisualStateGroup>
<VisualStateGroup x:Name="SelectionStates">
<VisualStateGroup.Transitions>
<VisualTransition GeneratedDuration="0"/>
</VisualStateGroup.Transitions>
<VisualState x:Name="Unselected"/>
<VisualState x:Name="Selected">
<Storyboard>
<DoubleAnimation Duration="0" To=".75" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="SelectedBackground"/>
</Storyboard>
</VisualState>
</VisualStateGroup>
<VisualStateGroup x:Name="CalendarButtonFocusStates">
<VisualStateGroup.Transitions>
<VisualTransition GeneratedDuration="0"/>
</VisualStateGroup.Transitions>
<VisualState x:Name="CalendarButtonFocused">
<Storyboard>
<ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="Visibility" Storyboard.TargetName="DayButtonFocusVisual">
<DiscreteObjectKeyFrame KeyTime="0">
<DiscreteObjectKeyFrame.Value>
<Visibility>Visible</Visibility>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="CalendarButtonUnfocused">
<Storyboard>
<ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="Visibility" Storyboard.TargetName="DayButtonFocusVisual">
<DiscreteObjectKeyFrame KeyTime="0">
<DiscreteObjectKeyFrame.Value>
<Visibility>Collapsed</Visibility>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
</VisualStateGroup>
<VisualStateGroup x:Name="ActiveStates">
<VisualStateGroup.Transitions>
<VisualTransition GeneratedDuration="0"/>
</VisualStateGroup.Transitions>
<VisualState x:Name="Active"/>
<VisualState x:Name="Inactive">
<Storyboard>
<ColorAnimation Duration="0" To="#FF777777" Storyboard.TargetProperty="(TextElement.Foreground).(SolidColorBrush.Color)" Storyboard.TargetName="NormalText"/>
</Storyboard>
</VisualState>
</VisualStateGroup>
<VisualStateGroup x:Name="DayStates">
<VisualStateGroup.Transitions>
<VisualTransition GeneratedDuration="0"/>
</VisualStateGroup.Transitions>
<VisualState x:Name="RegularDay"/>
<VisualState x:Name="Today">
<Storyboard>
<DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="TodayBackground"/>
<ColorAnimation Duration="0" To="#FFFFFFFF" Storyboard.TargetProperty="(TextElement.Foreground).(SolidColorBrush.Color)" Storyboard.TargetName="NormalText"/>
</Storyboard>
</VisualState>
</VisualStateGroup>
<VisualStateGroup x:Name="BlackoutDayStates">
<VisualStateGroup.Transitions>
<VisualTransition GeneratedDuration="0"/>
</VisualStateGroup.Transitions>
<VisualState x:Name="NormalDay"/>
<VisualState x:Name="BlackoutDay">
<Storyboard>
<DoubleAnimation Duration="0" To=".2" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="Blackout"/>
</Storyboard>
</VisualState>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<Rectangle x:Name="TodayBackground" Fill="#FFAAAAAA" Opacity="0" RadiusY="1" RadiusX="1"/>
<Rectangle x:Name="SelectedBackground" Fill="#FFBADDE9" Opacity="0" RadiusY="1" RadiusX="1"/>
<Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}"/>
<Rectangle x:Name="HighlightBackground" Fill="Red" Opacity="0" RadiusY="1" RadiusX="1"/>
<ContentPresenter x:Name="NormalText" TextElement.Foreground="#FF333333" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="5,1,5,1" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
<Path x:Name="Blackout" Data="M8.1772461,11.029181 L10.433105,11.029181 L11.700684,12.801641 L12.973633,11.029181 L15.191895,11.029181 L12.844727,13.999395 L15.21875,17.060919 L12.962891,17.060919 L11.673828,15.256231 L10.352539,17.060919 L8.1396484,17.060919 L10.519043,14.042364 z" Fill="#FF000000" HorizontalAlignment="Stretch" Margin="3" Opacity="0" RenderTransformOrigin="0.5,0.5" Stretch="Fill" VerticalAlignment="Stretch"/>
<Rectangle x:Name="DayButtonFocusVisual" IsHitTestVisible="false" RadiusY="1" RadiusX="1" Stroke="Red" Visibility="Collapsed"/>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Setter.Value>
</Setter>
<Setter Property="CalendarButtonStyle">
<Setter.Value>
<Style TargetType="{x:Type CalendarButton}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type CalendarButton}">
<Grid>
<VisualStateManager.VisualStateGroups>
<VisualStateGroup x:Name="CommonStates">
<VisualStateGroup.Transitions>
<VisualTransition GeneratedDuration="0:0:0.1"/>
</VisualStateGroup.Transitions>
<VisualState x:Name="Normal"/>
<VisualState x:Name="MouseOver">
<Storyboard>
<DoubleAnimation Duration="0" To="0.5" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="HighlightBackground"/>
</Storyboard>
</VisualState>
<VisualState x:Name="Pressed">
<Storyboard>
<DoubleAnimation Duration="0" To="0.5" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="HighlightBackground"/>
</Storyboard>
</VisualState>
<VisualState x:Name="Disabled">
<Storyboard>
<DoubleAnimation Duration="0" To="0" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="HighlightBackground"/>
<DoubleAnimation Duration="0" To=".35" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="NormalText"/>
</Storyboard>
</VisualState>
</VisualStateGroup>
<VisualStateGroup x:Name="SelectionStates">
<VisualStateGroup.Transitions>
<VisualTransition GeneratedDuration="0"/>
</VisualStateGroup.Transitions>
<VisualState x:Name="Unselected"/>
<VisualState x:Name="Selected">
<Storyboard>
<DoubleAnimation Duration="0" To=".75" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="SelectedBackground"/>
</Storyboard>
</VisualState>
</VisualStateGroup>
<VisualStateGroup x:Name="CalendarButtonFocusStates">
<VisualStateGroup.Transitions>
<VisualTransition GeneratedDuration="0"/>
</VisualStateGroup.Transitions>
<VisualState x:Name="CalendarButtonFocused">
<Storyboard>
<ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="Visibility" Storyboard.TargetName="ButtonFocusVisual">
<DiscreteObjectKeyFrame KeyTime="0">
<DiscreteObjectKeyFrame.Value>
<Visibility>Visible</Visibility>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="CalendarButtonUnfocused">
<Storyboard>
<ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="Visibility" Storyboard.TargetName="ButtonFocusVisual">
<DiscreteObjectKeyFrame KeyTime="0">
<DiscreteObjectKeyFrame.Value>
<Visibility>Collapsed</Visibility>
</DiscreteObjectKeyFrame.Value>
</DiscreteObjectKeyFrame>
</ObjectAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
</VisualStateGroup>
<VisualStateGroup x:Name="ActiveStates">
<VisualStateGroup.Transitions>
<VisualTransition GeneratedDuration="0"/>
</VisualStateGroup.Transitions>
<VisualState x:Name="Active"/>
<VisualState x:Name="Inactive">
<Storyboard>
<ColorAnimation Duration="0" To="#FF777777" Storyboard.TargetProperty="(TextElement.Foreground).(SolidColorBrush.Color)" Storyboard.TargetName="NormalText"/>
</Storyboard>
</VisualState>
</VisualStateGroup>
<VisualStateGroup x:Name="DayStates">
<VisualStateGroup.Transitions>
<VisualTransition GeneratedDuration="0"/>
</VisualStateGroup.Transitions>
<VisualState x:Name="RegularDay"/>
<VisualState x:Name="Today">
<Storyboard>
<DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="TodayBackground"/>
<ColorAnimation Duration="0" To="#FFFFFFFF" Storyboard.TargetProperty="(TextElement.Foreground).(SolidColorBrush.Color)" Storyboard.TargetName="NormalText"/>
</Storyboard>
</VisualState>
</VisualStateGroup>
<VisualStateGroup x:Name="BlackoutDayStates">
<VisualStateGroup.Transitions>
<VisualTransition GeneratedDuration="0"/>
</VisualStateGroup.Transitions>
<VisualState x:Name="NormalDay"/>
<VisualState x:Name="BlackoutDay">
<Storyboard>
<DoubleAnimation Duration="0" To=".2" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="Blackout"/>
</Storyboard>
</VisualState>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<Rectangle x:Name="TodayBackground" Fill="Red" Opacity="0" RadiusY="1" RadiusX="1"/>
<Rectangle x:Name="SelectedBackground" Fill="Red" Opacity="0" RadiusY="1" RadiusX="1"/>
<Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="#F6F9FB"/>
<Rectangle x:Name="HighlightBackground" Fill="Red" Opacity="0" RadiusY="1" RadiusX="1"/>
<ContentPresenter x:Name="NormalText" TextElement.Foreground="Black" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="5,1,5,1" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
<Path x:Name="Blackout" Data="M8.1772461,11.029181 L10.433105,11.029181 L11.700684,12.801641 L12.973633,11.029181 L15.191895,11.029181 L12.844727,13.999395 L15.21875,17.060919 L12.962891,17.060919 L11.673828,15.256231 L10.352539,17.060919 L8.1396484,17.060919 L10.519043,14.042364 z" Fill="#FF000000" HorizontalAlignment="Stretch" Margin="3" Opacity="0" RenderTransformOrigin="0.5,0.5" Stretch="Fill" VerticalAlignment="Stretch"/>
<Rectangle x:Name="ButtonFocusVisual" IsHitTestVisible="false" RadiusY="1" RadiusX="1" Stroke="Red" Visibility="Collapsed"/>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>