Styles.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:iconPacks="http://metro.mahapps.com/winfx/xaml/iconpacks">
    <Style x:Key="Styles.Button.Circle.Accent"
               BasedOn="{StaticResource MahApps.Styles.Button.Circle}"
               TargetType="{x:Type ButtonBase}">
        <Setter Property="Width" Value="48"/>
        <Setter Property="Height" Value="48"/>
        <Setter Property="Margin" Value="4"/>
        <Setter Property="Foreground" Value="{StaticResource MahApps.Brushes.Accent}" />
        <Setter Property="Background" Value="{StaticResource MahApps.Brushes.ThemeBackground}"/>
        <Style.Triggers>
            <Trigger Property="IsMouseOver" Value="True">
                <Setter Property="BorderBrush" Value="{StaticResource MahApps.Brushes.Accent}" />
            </Trigger>
            <Trigger Property="IsEnabled" Value="False">
                <Setter Property="Foreground" Value="{StaticResource MahApps.Brushes.Gray7}" />
            </Trigger>
        </Style.Triggers>
        <Style.Resources>

            <Style TargetType="iconPacks:PackIconMaterial" >
                <Setter Property="Width" Value="25"/>
                <Setter Property="Height" Value="auto"/>
                <Setter Property="HorizontalAlignment" Value="Center"/>
            </Style>

        </Style.Resources>
    </Style>
    <Style x:Key="Styles.Button.Circle.Accent2"
               BasedOn="{StaticResource Styles.Button.Circle.Accent}"
               TargetType="{x:Type ButtonBase}">
        <Setter Property="Width" Value="96"/>
        <Setter Property="Height" Value="96"/>
        <Setter Property="Margin" Value="4"/>
        <Style.Resources>
            <Style TargetType="iconPacks:PackIconMaterial" >
                <Setter Property="Width" Value="40"/>
                <Setter Property="Height" Value="auto"/>
                <Setter Property="HorizontalAlignment" Value="Center"/>
            </Style>

        </Style.Resources>
    </Style>
</ResourceDictionary>