wpf button style IsMouseOver

<style x:key="workbuttonstyle" targettype="{x:type button}">
            <style.triggers>
                <trigger property="ismouseover" value="false">
                    <setter property="fontsize" value="20"/>
                </trigger>
                <trigger property="ismouseover" value="true">
                    <setter property="fontsize" value="30"/>
                </trigger>
            </style.triggers>
        </style>

<style x:key="closebuttonstyle" targettype="{x:type button}">
            <style.triggers>
                <trigger property="ismouseover" value="false">
                    <setter property="content">
                        <setter.value>
                            <image source="/at;component/resource/images/closetrue.jpg"/>
                        </setter.value>
                    </setter>
                </trigger>
                <trigger property="ismouseover" value="true">
                    <setter property="content">
                        <setter.value>
                            <image source="/at;component/resource/images/close.jpg"/>
                        </setter.value>
                    </setter>
                </trigger>
            </style.triggers>
        </style>