body{
    margin: -1em;
    padding: 0;
    overflow: hidden;
}

.header-img{
    margin: 0;
    padding: 0;
    text-align: center;
    width: 100%;
    max-width: calc(100vw + 2em);
    height: auto;
    max-height: calc(100vh);
    overflow: hidden;
}

.header-img.landscape{
    display: block;
}

.landscape-img.portrait{
    display: none;
}

@media only screen and (orientation: portrait) {

.header-img.landscape{
    display: none;
}

.landscape-img.portrait{
    display: block;
}
}