MacButtonStyle.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Style x:Key="MacButtonStyle" TargetType="Button">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="Button">
                    <Grid>
                        <Ellipse Fill="{TemplateBinding Background}"/>
                        <ContentPresenter x:Name="ContentPresenter" HorizontalAlignment="Center" VerticalAlignment="Center" Visibility="Hidden"/>
                        <Ellipse x:Name="HoverEllipse" Fill="White" Opacity="0.2" Visibility="Hidden"/>
                    </Grid>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsMouseOver" Value="True">
                            <Setter Property="Cursor" Value="Hand"/>
                            <Setter TargetName="HoverEllipse" Property="Visibility" Value="Visible"/>
                            <Setter TargetName="ContentPresenter" Property="Visibility" Value="Visible"/>
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>