<Style TargetType="Button" x:Key="buttonStyle">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="Button">
                        <!--Define the ControlTemplate here.-->
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>

 <Button Width="100" Height="40" Content="Hello" Style="{StaticResource buttonStyle}" />