js get position from center from center of element code example
Example 1: center div in middle of page
.centered {
position: fixed;
top: 50%;
left: 50%;
/* bring your own prefixes */
transform: translate(-50%, -50%);
}
Example 2: how to center a position fixed element horizontally
left: 50%;
margin-left: -400px; /* Half of the width */