How do I get the content to be centered when the page shrinks?

Most Web sites on the Web can be centered after the page is zoomed out. For example CSDN can also.
I hope my own station can also ah my own development of the station, after narrowing, the contents of all to the upper left corner, good entanglements, I want to be the same as the mainstream AH. How should CSS be designed? or which CSS tag can be implemented? Or what method can be implemented with CSDN this function, please guide. ~~

Reply to discussion (solution)

That's because your page defaults to the left, and the narrowing is not off.
See below:

Define margin:0 Auto, can be left and right center

Upstairs positive solution to set Div margin:0 auto;

