.centered-box {
position: fixed;
top: 50%;
left: 50%;
width: 300px;
/* bring your own prefixes */
transform: translate(-50%, -50%);
}
.centered-box {
position: fixed;
top: 50%;
left: 50%;
width: 300px;
/* bring your own prefixes */
transform: translate(-50%, -50%);
}