How do I convert this code?

[Igor Korot <ikorot01 gmail com>]

Hi, ALL,
In my GTK+-2 I have a following code:

        const GtkBorder* oldBorder = gtk_entry_get_inner_border(entry);

Unfortunately this function is deprecated in GTK+-3.4.
Now the documentation suggests to use GtkStyleContext and GtkCssProvider.

Looking at GtkStyleContext I see that it has gtk_style_context_get_border().
However, this function first parameter is "GtkStyleContext *".

So what would be the proper code replacement?
Should I construct a blank GtkStyleContext? But then how to attach it
to the widget? Or I am looking at it completely wrong?

Thank you for any pointers you can provide.