This is the button original style, understand how to change the love how to change
<Window.Resources>
<style x:key= "Buttonfocusvisual" >
<setter property= "Control.template" >
<Setter.Value>
<ControlTemplate>
<rectangle stroke= "Black" strokedasharray= "1 2" strokethickness= "1" margin= "2" snapstodevicepixels= "true"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<lineargradientbrush x:key= "Buttonnormalbackground" endpoint= "0,1" startpoint= "0,0" >
<gradientstop color= "#F3F3F3" offset= "0"/>
<gradientstop color= "#EBEBEB" offset= "0.5"/>
<gradientstop color= "#DDDDDD" offset= "0.5"/>
<gradientstop color= "#CDCDCD" offset= "1"/>
</LinearGradientBrush>
<solidcolorbrush x:key= "Buttonnormalborder" color= "#FF707070"/>
<style x:key= "ButtonStyle1" targettype= "{x:type button}" >
<setter property= "FocusVisualStyle" value= "{StaticResource buttonfocusvisual}"/>
<setter property= "Background" value= "{StaticResource buttonnormalbackground}"/>
<setter property= "BorderBrush" value= "{StaticResource buttonnormalborder}"/>
<setter property= "BorderThickness" value= "1"/>
<setter property= "Foreground" value= "{dynamicresource {x:static Systemcolors.controltextbrushkey}}"/>
<setter property= "horizontalcontentalignment" value= "Center"/>
<setter property= "verticalcontentalignment" value= "Center"/>
<setter property= "Padding" value= "1"/>
<setter property= "Template" >
<Setter.Value>
<controltemplate targettype= "{x:type button}" >
<microsoft_windows_themes:buttonchrome x:name= "Chrome" snapstodevicepixels= "true" background= "{TemplateBinding Background} "borderbrush=" {TemplateBinding BorderBrush} "renderdefaulted=" {TemplateBinding isdefaulted} " Rendermouseover= "{TemplateBinding ismouseover}" renderpressed= "{TemplateBinding ispressed}" >
<contentpresenter horizontalalignment= "{TemplateBinding horizontalcontentalignment}" margin= "{TemplateBinding Padding} "verticalalignment=" {TemplateBinding verticalcontentalignment} "snapstodevicepixels=" {TemplateBinding Snapstodevicepixels} "recognizesaccesskey=" True "/>
</Microsoft_Windows_Themes:ButtonChrome>
<ControlTemplate.Triggers>
<trigger property= "iskeyboardfocused" value= "true" >
<setter property= "renderdefaulted" targetname= "Chrome" value= "true"/>
</Trigger>
<trigger property= "togglebutton.ischecked" value= "true" >
<setter property= "renderpressed" targetname= "Chrome" value= "true"/>
</Trigger>
<trigger property= "IsEnabled" value= "false" >
<setter property= "Foreground" value= "#ADADAD"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
WPF Button Style Original template