How to Change Mega Menu Size and Center It?

So I read this: https://docs.generatepress.com/article/building-simple-mega-menu/

and inside the CSS code, this part I tried to change:

From this:

nav .main-nav .mega-menu > ul {
position: absolute;
width: 100%;
left: 0 !important;
display: flex;
flex-wrap: wrap;
}

To this:

nav .main-nav .mega-menu > ul {
position: absolute;
width: 90%;
center: 0 !important;
display: flex;
flex-wrap: wrap;
}

So I only changed width and from "left" to "center" but for some reason the word "center" doesn't work. How can I center the mega menu after I changed the width? Thanks