Nebula-Auth/NebulaAuth/Theme/MaterialDesignThemes.Overrides.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"                                     
                    xmlns:materialDesign="clr-namespace:MaterialDesignThemes.Wpf;assembly=MaterialDesignThemes.Wpf">

    <Style BasedOn="{StaticResource MaterialDesignLinearProgressBar}" TargetType="{x:Type ProgressBar}">
        <Setter Property="Background" Value="{DynamicResource Base200Brush}" />
        <Setter Property="BorderThickness" Value="0" />
    </Style>

    <Style x:Key="MaterialDesignLinearProgressBar" BasedOn="{StaticResource MaterialDesignLinearProgressBar}" TargetType="{x:Type ProgressBar}">
        <Setter Property="Background" Value="{DynamicResource Base200Brush}" />
        <Setter Property="BorderThickness" Value="0" />
    </Style>

    <!--If style is not default like above, x:key must be provided (the same as BasedOn)-->

</ResourceDictionary>