WPF set border background in trigger
Common mistake. You have set the Border.Background property directly which will always override the value set by your trigger. (Locally set values have a very high precedence, style has a pretty low precedence.)
Instead, you should move your "normal" background into the Style like so:
<Border> <Border.Style> <Style TargetType="Border"> <Setter Property="Background"> <Setter.Value> <LinearGradientBrush> <LinearGradientBrush.GradientStops> <GradientStop Color="Aquamarine" Offset="0"/> </LinearGradientBrush.GradientStops> </LinearGradientBrush> </Setter.Value> </Setter> <Style.Triggers> <!-- the trigger you showed --> </Style.Triggers> </Style> </Border.Style></Border>