如何将TextBlock的字体大小设置为另一个字体大小属性的比率？

<TextBlock FontSize="12" Text="Hello World!" />

private double _ratio;
public double Ratio
{
    get { return _ratio; }
    set
    {
        if (_ratio != value)
        {
            _ratio = value;
            OnPropertyChanged("Ratio");
        }
    }
}

public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}

<TextBlock FontSize="{Binding Ratio, Converter={StaticResource RatioToFontSizeConverter}}" Text="Hello World!" />

public class RatioToFontSizeConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        double ratio = (double)value;
        double baseFontSize = 12; // 固定的字体大小
        double fontSize = baseFontSize * ratio;
        return fontSize;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}