QuickLook/QuickLook/MainWindowTransparent.xaml

<Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:fa="http://schemas.fontawesome.io/icons/"
    xmlns:local="clr-namespace:QuickLook"
    xmlns:control="clr-namespace:QuickLook.Controls"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:converters="clr-namespace:QuickLook.Converters"
    mc:Ignorable="d" x:Class="QuickLook.MainWindowTransparent" x:Name="mainWindow"
    UseLayoutRounding="True"
    d:DesignWidth="624" d:DesignHeight="700"
    MinWidth="275" MinHeight="150"
    WindowStartupLocation="CenterScreen"
    Focusable="False" WindowStyle="None"
    Background="#E5FAFAFA" AllowsTransparency="True"
    ShowActivated="False" ShowInTaskbar="False"
    FontFamily="Segoe UI,Microsoft Yahei UI">
    <Window.Resources>
        <converters:BooleanToResizeModeConverter x:Key="BooleanToResizeModeConverter" />
        <converters:BooleanToResizeBorderThicknessConverter x:Key="BooleanToResizeBorderThicknessConverter" />
    </Window.Resources>
    <Window.ResizeMode>
        <Binding Converter="{StaticResource BooleanToResizeModeConverter}" ElementName="mainWindow"
                 Path="ContextObject.CanResize" />
    </Window.ResizeMode>
    <WindowChrome.WindowChrome>
        <WindowChrome CaptionHeight="{Binding Height, ElementName=titlebar}"
                      ResizeBorderThickness="{Binding ContextObject.CanResize, Converter={StaticResource BooleanToResizeBorderThicknessConverter}, ElementName=mainWindow}"
                      UseAeroCaptionButtons="False" />
    </WindowChrome.WindowChrome>
    <Border x:Name="windowBorder" BorderThickness="1" BorderBrush="#FF7B7B7B">
        <Grid>
            <DockPanel x:Name="windowPanel">
                <DockPanel.Style>
                    <Style TargetType="{x:Type DockPanel}">
                        <Style.Triggers>
                            <DataTrigger Binding="{Binding ContextObject.IsBusy, ElementName=mainWindow, Mode=OneWay}"
                                         Value="False">
                                <DataTrigger.EnterActions>
                                    <BeginStoryboard>
                                        <Storyboard>
                                            <DoubleAnimation Storyboard.TargetProperty="Opacity" From="0" To="1"
                                                             BeginTime="0:0:0" Duration="0:0:0" />
                                        </Storyboard>
                                    </BeginStoryboard>
                                </DataTrigger.EnterActions>
                                <DataTrigger.ExitActions>
                                    <BeginStoryboard>
                                        <Storyboard>
                                            <DoubleAnimation Storyboard.TargetProperty="Opacity" From="1" To="0"
                                                             BeginTime="0:0:0" Duration="0:0:0" />
                                        </Storyboard>
                                    </BeginStoryboard>
                                </DataTrigger.ExitActions>
                            </DataTrigger>
                        </Style.Triggers>
                    </Style>
                </DockPanel.Style>
                <DockPanel x:Name="titlebar" Height="28" Dock="Top">
                    <fa:ImageAwesome DockPanel.Dock="Right" x:Name="buttonCloseWindow" Icon="TimesCircle"
                                     WindowChrome.IsHitTestVisibleInChrome="True"
                                     Height="15" Margin="10,0" Foreground="Gray"
                                     Cursor="Hand" />
                    <Button x:Name="buttonOpenWith" DockPanel.Dock="Right" Content="Open with ..." Height="20"
                            Margin="10,0,0,0" Padding="5,0"
                            Focusable="False" Cursor="Hand"
                            Background="#E5EEEEEE" BorderBrush="#E59A9A9A"
                            WindowChrome.IsHitTestVisibleInChrome="True" Foreground="#FF404040" />
                    <!-- set grid.background colour makes it clickable -->
                    <Grid x:Name="titleArea" Background="Transparent">
                        <TextBlock Text="{Binding ContextObject.Title, ElementName=mainWindow}" FontSize="14"
                                   HorizontalAlignment="Center"
                                   VerticalAlignment="Center" />
                    </Grid>
                </DockPanel>
                <Grid>
                    <ContentControl x:Name="container"
                                    Content="{Binding ContextObject.ViewerContent, ElementName=mainWindow}" />
                </Grid>
            </DockPanel>
            <Grid x:Name="busyIndicatorLayer">
                <Grid.Style>
                    <Style TargetType="{x:Type Grid}">
                        <Style.Triggers>
                            <DataTrigger Binding="{Binding ContextObject.IsBusy, ElementName=mainWindow, Mode=OneWay}"
                                         Value="False">
                                <DataTrigger.EnterActions>
                                    <BeginStoryboard>
                                        <Storyboard>
                                            <ParallelTimeline>
                                                <DoubleAnimation Storyboard.TargetProperty="Opacity" From="1" To="0"
                                                                 BeginTime="0:0:0" Duration="0:0:0.05" />
                                                <ObjectAnimationUsingKeyFrames
                                                    Storyboard.TargetProperty="(UIElement.Visibility)">
                                                    <DiscreteObjectKeyFrame KeyTime="0:0:0.05"
                                                                            Value="{x:Static Visibility.Hidden}" />
                                                </ObjectAnimationUsingKeyFrames>
                                            </ParallelTimeline>
                                        </Storyboard>
                                    </BeginStoryboard>
                                </DataTrigger.EnterActions>
                                <DataTrigger.ExitActions>
                                    <BeginStoryboard>
                                        <Storyboard>
                                            <ParallelTimeline>
                                                <DoubleAnimation Storyboard.TargetProperty="Opacity" From="0" To="1"
                                                                 BeginTime="0:0:0" Duration="0:0:0" />
                                                <ObjectAnimationUsingKeyFrames
                                                    Storyboard.TargetProperty="(UIElement.Visibility)">
                                                    <DiscreteObjectKeyFrame KeyTime="0:0:0"
                                                                            Value="{x:Static Visibility.Visible}" />
                                                </ObjectAnimationUsingKeyFrames>
                                            </ParallelTimeline>
                                        </Storyboard>
                                    </BeginStoryboard>
                                </DataTrigger.ExitActions>
                            </DataTrigger>
                        </Style.Triggers>
                    </Style>
                </Grid.Style>
                <!--IsBusyIndicatorShowing="{Binding IsVisible, ElementName=busyIndicatorLayer}"-->
                <control:BusyDecorator x:Name="busyDecorator"
                                       IsBusyIndicatorShowing="True"
                                       VerticalAlignment="Center"
                                       HorizontalAlignment="Center" />
            </Grid>
        </Grid>
    </Border>
</Window>