Swapping css

Swapping a css style-sheet with another web page can be an  interesting result. After swapping my css with two other individuals the results were interesting and not what i expected. The first page that i swapped with turned out decent, My content and navigation was seen, but there apparently was a div overlapping another div. 

Second swapping turned out actually better. The main difference was that the content was right in the center, unlike my own css which had the content toward the right.

Also the third css sheet that belonged to casabasa.com turned out also with unexpected results to me. It came out fine tough, once again content was centered and the results with this were actually positive.