Java inner classes in c#

I have the following Java code:

public class A {
    private int var_a = 666;

    public A() {
        B b = new B();
        b.method123();
        System.out.println(b.var_b);
    }

    public class B {
        private int var_b = 999;

        public void method123() {
            System.out.println(A.this.var_a);           
        }
    }
}

Which yields 666 and 999. Now, I've tried to set up similar code in c#, but it seems that it is not possible to accomplish the same. If that's the case, how you usually achieve a similar effect when programming in c#?