<14.O-O-O Re8 Main problem of [Black] is piece coordination.His King is stuck between two Rooks, Knight on f5 is nice target which makes Bishop on d6 very vulnerable.
17.g3 Making room for Bishop [and denying f4 to the black bishop]
19.bxc3! Concrete approach! 19.Nxc3 is good, yes 19...Rxe1 20.Rxe1 Kd7 21.Nd5 or 21.Ne4 with edge but Black can catch his breath.With Rook on d1 Black cannot establish connection between Rooks.
21.Nxd6+? No.21.Bh3+ is much better in order to provoke 21..f5 22.Nxd6+ cxd6 23.Rxe5 Nxe5 24.Rxd6 Kc7 25.Re6 and Black is walking on thin ice.
Now task is much harder to reach.
24.Re6 Rd8 Black is pawn down but doubled pawns are serious illness of White.Chance to build up a blockade on dark squares are high.
26.Bd3 h6 Path to Kingside is open but it's not easy to cross e-file.
Black must hold on to dark squares, 30...Kb6 31.Kc3 Kc5 is best for Black, it's uneasy job to make progress as White.
36.c5 From now on White is healthy pawn up, in other words he is winning.>