Styles in WPF

A Style is a resource-dictionary object that bundles a set of Setter elements — property/value pairs — and applies them to every control matched by TargetType or explicitly assigned via the Style property. Instead of repeating FontSize="14" Foreground="#333" Padding="8" on every Button in a window, you define one Style once as a resource and either key it explicitly (x:Key="PrimaryButton") for opt-in use, or omit x:Key to make it implicit, applying automatically to every Button of that exact TargetType within its resource scope.

Styles support single inheritance via BasedOn="{StaticResource ParentStyle}", which lets a specialized style (e.g. DangerButtonStyle) inherit every Setter from a base style (BaseButtonStyle) and then override or add only the properties that differ, such as Background="Red". TargetType is mandatory whenever a Style contains Setters for properties not on the base UIElement/FrameworkElement (like Button.IsDefault), and an implicit style's TargetType must match the exact runtime type of the elements it targets — a Style TargetType="ButtonBase" without an x:Key will NOT implicitly apply to Button instances, since implicit matching checks the concrete type, not the inheritance chain.

A Style can contain a Style.Triggers collection with Trigger, MultiTrigger, DataTrigger and MultiDataTrigger elements that conditionally apply extra Setters — for example, a Trigger on IsMouseOver="True" that changes Background, without needing a full ControlTemplate. Unlike ControlTemplate.Triggers, Style-level Triggers set properties directly on the styled control itself (no TargetName needed for the control's own properties), which makes Style triggers the simplest tool for conditional appearance changes that don't require restructuring the visual tree.