<Style x:Key="MyCheckBox" TargetType="{x:Type CheckBox}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type CheckBox}">

            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

<Setter Property="Foreground" Value="#FF000000"/>
<Setter Property="Background" Value="#FFA4CE36"/>
<Setter Property="MaxWidth" Value="100"/>
<Setter Property="MaxHeight" Value="100"/>
<Setter Property="FontSize" Value="40"/>
<Setter Property="FontWeight" Value="DemiBold"/>

<ControlTemplate TargetType="{x:Type CheckBox}">
    <Border Width="{TemplateBinding Width}"
            Height="{TemplateBinding Height}"
            BorderBrush="#33000000"
            BorderThickness="1"
            CornerRadius="25"
            Background="{TemplateBinding Background}">

        <ContentPresenter x:Name="contentPresenter"
                          Focusable="False"
                          HorizontalAlignment="Center"
                          VerticalAlignment="Center"
                          Margin="{TemplateBinding Padding}"
                          RecognizesAccessKey="True"
                          SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" />
    </Border>
</ControlTemplate>

<ControlTemplate.Triggers>
    <Trigger Property="IsChecked" Value="true">
        <Setter Property="Foreground" Value="White"/>
    </Trigger>
</ControlTemplate.Triggers>

<Style x:Key="MyCheckBox" TargetType="{x:Type CheckBox}">
    <Setter Property="Foreground" Value="#FF000000"/>
    <Setter Property="Background" Value="#FFA4CE36"/>
    <Setter Property="MaxWidth" Value="100"/>
    <Setter Property="MaxHeight" Value="100"/>
    <Setter Property="FontSize" Value="40"/>
    <Setter Property="FontWeight" Value="DemiBold"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type CheckBox}">
                <Border Width="{TemplateBinding Width}"
                        Height="{TemplateBinding Height}"
                        BorderBrush="#33000000"
                        BorderThickness="1"
                        CornerRadius="25"
                        Background="{TemplateBinding Background}">

                    <ContentPresenter x:Name="contentPresenter"
                                      Focusable="False"
                                      HorizontalAlignment="Center"
                                      VerticalAlignment="Center"
                                      Margin="{TemplateBinding Padding}"
                                      RecognizesAccessKey="True"
                                      SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" />
                </Border>

                <ControlTemplate.Triggers>
                    <Trigger Property="IsChecked" Value="true">
                        <Setter Property="Foreground" Value="White"/>
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

<CheckBox Style="{DynamicResource MyCheckBox}" Content="1" />