memory usage of x:Static vs StaticResource

what is the memory usage of x:static values? are they hold in the memory all the time if class is not static bu only member like below

public partial class  Styles
    {
        public static  int ItemSize = 15;
}

I guess StaticResources are hold in memory if only defined in App.xaml or app.xaml.cs. if defined in the contentpage, once contentpage is disposed, they are as well. is it correct? so using StaticResources have more advantage over x:static. ?