Themes/MaterialDesignTheme.Label.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <Style x:Key="MaterialDesignLabel" TargetType="{x:Type Label}">
    <Setter Property="Background" Value="Transparent" />
    <Setter Property="Foreground" Value="{DynamicResource MaterialDesign.Brush.Foreground}" />
    <Setter Property="HorizontalContentAlignment" Value="Left" />
    <Setter Property="Padding" Value="4" />
    <Setter Property="Template">
      <Setter.Value>
        <ControlTemplate TargetType="{x:Type Label}">
          <Border Padding="{TemplateBinding Padding}"
                  Background="{TemplateBinding Background}"
                  BorderBrush="{TemplateBinding BorderBrush}"
                  BorderThickness="{TemplateBinding BorderThickness}"
                  SnapsToDevicePixels="true">
            <ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                              VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                              RecognizesAccessKey="True"
                              SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" />
          </Border>
          <ControlTemplate.Triggers>
            <Trigger Property="IsEnabled" Value="false">
              <Setter Property="Opacity" Value=".56" />
            </Trigger>
          </ControlTemplate.Triggers>
        </ControlTemplate>
      </Setter.Value>
    </Setter>
    <Setter Property="VerticalContentAlignment" Value="Top" />
  </Style>
</ResourceDictionary>