* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    min-height: 100vh;
    display: flex;
    align-items: center;      /* vertical center */
    justify-content: center;  /* horizontal center */
    background: #ffffff;
}

.banner {
    width: 100vw;      /* always full viewport width */
    height: auto;
    display: block;
}