<Window x:Class="Main" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="" Height="300" Width="300"> <Window.Resources> <Storyboard x:Key="LowOpacity"> <DoubleAnimation Storyboard.TargetProperty="Opacity" /> </Storyboard> <Storyboard x:Key="HighOpacity"> <DoubleAnimation Storyboard.TargetProperty="Opacity" To="1" AutoReverse="True" RepeatBehavior="Forever" /> </Storyboard> </Window.Resources> <Grid> <Grid.ColumnDefinitions> <ColumnDefinition Width="0.5*" /> <ColumnDefinition Width="0.5*" /> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition Height="*" /> <RowDefinition Height="35" /> </Grid.RowDefinitions> <Border Background="Firebrick" Width="100" Height="100" x:Name="Rect1" Opacity="0.4"> <Border.Triggers> <EventTrigger RoutedEvent="Mouse.MouseEnter"> <BeginStoryboard Storyboard="{DynamicResource HighOpacity}" /> </EventTrigger> <EventTrigger RoutedEvent="Mouse.MouseLeave"> <BeginStoryboard Storyboard="{DynamicResource LowOpacity}" /> </EventTrigger> </Border.Triggers> </Border> <Rectangle Fill="Firebrick" Width="100" Height="100" Grid.Column="1" /> </Grid> </Window>