About absolute position: How to center div in fixed

Maybe I like it too much. My blog has been changing for three days. I think it is better to center navigation by using jquery + css at the front end. At the beginning, css wrote: div {position: fixed;

Maybe I like it too much. My blog has been changing for three days. I think it is better to center navigation by using jquery + css at the front end.

At the beginning, css was written as follows:

Div {position: fixed; top: 0; margin: 0 auto; z-index: 999 ;}

The div cannot be centered. The solution is as follows:

Div {position: fixed; top: 0; left: 0; right: 0; margin: auto; z-index: 999}

I am afraid that I will change my mind tomorrow. The screenshot is as follows: