How do I center this code in the middle of the page?

HTML & CSS
59

What causes these differences?

50 Right 50 Left [table]

50 + 50 = 10 + 2 = 102

vs.

49 Right 49 Left [flexbot]

49 + 49 = 98 + 2 = 100

the + 2 is the blue in the middle.