<Window x:Class="WpfApplication1.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="WPF" Height="160" Width="300"> <Window.Resources> <Style TargetType="{x:Type ToolTip}"> <Setter Property="Width" Value="100"/> <Setter Property="Height" Value="100"/> <Setter Property="OverridesDefaultStyle" Value="True"/> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="{x:Type ToolTip}"> <Border Name="Border" BorderBrush="DarkGray" BorderThickness="1" Width="{TemplateBinding Width}" Height="{TemplateBinding Height}" CornerRadius="4"> <Border.Background> <LinearGradientBrush StartPoint="0,0" EndPoint="0,1"> <GradientStop Color="Snow" Offset="0.0"/> <GradientStop Color="Gainsboro" Offset="1.0"/> </LinearGradientBrush> </Border.Background> </Border> </ControlTemplate> </Setter.Value> </Setter> </Style> </Window.Resources> <Grid> <TextBlock Foreground="DarkGray" VerticalAlignment="Center" HorizontalAlignment="Center" ToolTip="This is a custom tooltip" Text="Mouse Over for tooltip"/> </Grid> </Window>