ControlTemplate and Style are not applied to the CustomDialog

[AlanWills]

What steps will reproduce this issue?

I have a custom message window using the CustomDialog control with the following XAML:

<Dialogs:CustomDialog x:Class="Viewer.AM.Windows.MessageWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Viewer.AM.Windows"
        xmlns:Dialogs="clr-namespace:MahApps.Metro.Controls.Dialogs;assembly=MahApps.Metro"
        mc:Ignorable="d"
        Style="{DynamicResource NewCustomDialogStyle}">
</Dialogs:CustomDialog>

and the Style is copied from this stack overflow question:

http://stackoverflow.com/questions/30751663/how-to-change-mahapps-metro-dialog-content-template-width

<Style TargetType="{x:Type Dialog:BaseMetroDialog}"
        x:Key="NewCustomDialogStyle"
        BasedOn="{StaticResource {x:Type Dialog:BaseMetroDialog}}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type Dialog:BaseMetroDialog}">
                <ControlTemplate.Resources>
                    <Storyboard x:Key="DialogShownStoryboard">
                        <DoubleAnimation AccelerationRatio=".9"
                                            BeginTime="0:0:0"
                                            Duration="0:0:0.2"
                                            Storyboard.TargetProperty="Opacity"
                                            To="1" />
                    </Storyboard>
                </ControlTemplate.Resources>
                <Grid Background="{TemplateBinding Background}">
                    <Border FocusVisualStyle="{x:Null}"
                            Focusable="False">
                        <Grid>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="Auto" />
                                <RowDefinition Height="*" />
                                <RowDefinition Height="Auto" />
                            </Grid.RowDefinitions>
                            <ContentPresenter Grid.Row="0"
                                                Content="{TemplateBinding DialogTop}" />
                            <Grid Grid.Row="1">
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="10*" />
                                    <ColumnDefinition Width="80*" />
                                    <ColumnDefinition Width="10*" />
                                </Grid.ColumnDefinitions>
                                <!--  Content area  -->
                                <Grid Grid.Column="1"
                                        Margin="0 10 0 0">
                                    <Grid.RowDefinitions>
                                        <RowDefinition Height="Auto" />
                                        <RowDefinition Height="*" />
                                    </Grid.RowDefinitions>
                                    <TextBlock Grid.Row="0"
                                                FontSize="{DynamicResource DialogTitleFontSize}"
                                                Foreground="{TemplateBinding Foreground}"
                                                Text="{TemplateBinding Title}"
                                                TextWrapping="Wrap" />
                                    <ContentPresenter Grid.Row="1"
                                                        Content="{TemplateBinding Content}" />
                                </Grid>
                            </Grid>
                            <ContentPresenter Grid.Row="2"
                                                Content="{TemplateBinding DialogBottom}" />
                        </Grid>
                    </Border>
                </Grid>
                <ControlTemplate.Triggers>
                    <EventTrigger RoutedEvent="Loaded">
                        <EventTrigger.Actions>
                            <BeginStoryboard Storyboard="{StaticResource DialogShownStoryboard}" />
                        </EventTrigger.Actions>
                    </EventTrigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

Expected outcome

Changing the style is echoed in the designer - when I change the background colour of the grid for example, but at runtime it is not applied. When inspecting with the Visual Tree, the style seems to be coming from the BaseMetroDialog.

I have been able to style other metro UI elements successfully, so why is this not working?

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Environment

• MahApps.Metro v1.4.1
• Windows 10
• Visual Studio 2015
• .NET Framework 4.5.2