How to horizontally center a rubber block that has max-width?

Question

css

Is it possible to do this without js and cross browser?
Current Block Styles

.popup {
    background: #fff;
    position: fixed;
    width: 70%;
    z-index: 99999999;
    left: 15%;
    top: 10%;
    max-width: 900px;
}

Answer 1

.popup {
    position: fixed;
    width: 70%;
    left: 0;
    right: 0;
    top: 10%;
    max-width: 900px;
    background: #000;
    margin: 0 auto;
}

This is how it works and seems to be cross-browser

Answer 2

Like this: jsfiddle.net/IonDen/jrqaw5se

.popup {
    position: fixed;
    width: 70%;
    left: 50%;
    top: 10%;
    max-width: 900px;
    transform: translate(-50%, 0);
    background: #000;
}

Answer 3

addmargin: 0 auto;