header {
    height: 120px;
    text-align: center;
    overflow: hidden;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    background: #fff;
}
header img {
    width: auto;
    height: 120px;
}

main {
    height: auto;
    min-height: 100vh;
    padding: 150px;
}