Center image fullscreen using flexbox

place image fullscreen css code

.flexContainer {
    display: flex;
}
.flexCenter {
    justify-content: center;
}
.fullHeight {
    height: 100vh;
}
.itemCenter {
    align-items: center;
}
.fullHeight {
    height: 100vh;
}
.centerImage {
    background: url('images/ocean.jpg') center;
    background-size: cover;
}