header {
    position: fixed;
    top: 0;
    left: 0;
    z-index: 50;
    padding: 34px 45px;
}

header .logo_box {
    width: 110px;
}

header .logo_box img {
    width: 100%;
}

@media screen and (max-width:768px) {
    header {
        padding: 25px;
    }

    header .logo_box {
        width: 70px;
    }
}