Style to set Focus

   <Style TargetType="TextBox" x:Key="MaterialDesignFloatingHintTextBoxWithFocus" BasedOn="{StaticResource MaterialDesignFloatingHintTextBox}">
        <Style.Triggers>
            <DataTrigger Binding="{Binding RelativeSource={RelativeSource Self}, Path=IsVisible}" Value="True">
                <Setter Property="FocusManager.FocusedElement" Value="{Binding RelativeSource={RelativeSource Self}}"/>
            </DataTrigger>
        </Style.Triggers>
    </Style>
    <Style TargetType="PasswordBox" x:Key="PasswordBoxWithFocus" BasedOn="{StaticResource MaterialDesignPasswordBox}">
        <Style.Triggers>
            <DataTrigger Binding="{Binding RelativeSource={RelativeSource Self}, Path=IsVisible}" Value="True">
                <Setter Property="FocusManager.FocusedElement" Value="{Binding RelativeSource={RelativeSource Self}}"/>
            </DataTrigger>
        </Style.Triggers>
    </Style>