How does White crumble Black's center? Negi suggests 18.Kh1!N but it seems Black can continue to push his pawns.

[FEN ""]
[White ""]
[Black ""]
[Event ""]
[Site ""]
[Result "*"]
[ECO "B33"]
[Date "????.??.??"]

1. e4 c5 2. Nf3 Nc6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 e5 6. Ndb5 d6 7. Bg5 a6 8. Na3 
b5 9. Bxf6 gxf6 10. Nd5 f5 11. Bd3 Be6 12. c3 Bg7 13. Nxb5 Bxd5 14. exd5 Ne7 15. 
Na3 O-O (15... e4 16. Qa4+ Kf8 (16... Qd7 17. Bb5 ) ) 16. O-O e4 17. Bc2 Rc8 
18. Kh1 (18. Qh5 Rc5 ) (18. f3 Qb6+ $19 ) Rc5 (18... Qb6 19. Bb3 $16 ) 19. f3 Rxd5 
20. Qe2 (20. Qb1 Qb8 21. fxe4 fxe4 22. Bxe4 Rh5 {threatening ...d5} 23. Bf3 Rh6 
24. Bg4 f5 {The Black center is gone, but Black doesn't stand bad either: White's 
Queen and a1 rook are misplaced.} 25. Bh3 $4 Rxh3 26. gxh3 Qb7+ 27. Kg1 Rf6 $19 
) Re5 21. Nc4 Re6 22. Bb3 d5 23. Rad1 Kh8 24. Ne3 Rd6 25. fxe4 fxe4


Does White just wait for Black to overextend?
I have no idea why @Maxwell86 was downvoted. He is correct that Blacks pawns look impressive but it is not easy to see what to do with them.
The pawns are strong if they restrict Whites pieces, or if they are mobile enough to generate threats. Neither is the case here. I would regard 16..e4 as a positional blunder, because it fixes the pawn structure, and allows White to form a plan around it. This might be along the lines of Bc2-Bb3 (hold that QP), f2-f4(giving Black a protected passed pawn, but it isnt going anywhere, and White prevents Black from connecting up his Pawns with an eventual ..f4), Na3-c2-e3 (A perfect square, blockading and influencing both wings), Ra1-b1 or Qd1-d2 (protect the b-Pawn) then in due course c2-c4, Bb3-a4, b2-b4, lauching a Pawn avalanche on the Q-side.

Yes, of course Black gets to move also, but I dont see anything like this plan of campaign. White seems to me to have a big advantage because his Pawns are (or will become) mobile and Blacks will not. Whites strategy in this sort of position is always to advance on the Q-side, while Black usually looks for counterplay on the K-side, but this will not be easy with his pawns blockaded. They hardly restrict White from doing what he wishes, and they cant generate threats. It does take time for White to do everything but Blacks play is even slower. White has only one potential weakness (on g2, which the N already protects. Black will try things like Bg7-h6, Rf8-g8, Qd8-f6-g6, Ne7-g6-h4, against which White has Rf1-f2, Qd1-d2.

There is still a game ahead, but it will be the kind of game where each player forms a plan and tries to achieve their own while frustrating the oponent. My money is on White.