html, body {
    height: 100%;
    width: 100%;
    display: inline;
}

#ski {
    height: 100%;
    width: 50%;
    float: left;
}

#sun {
    height: 100%;
    width: 50%;
    float: left;
}

#ski img {
    width: 100%;
}

#sun img {
    width: 100%;
}

img {
    transition: opacity 2s;
}

img:hover {
    opacity: 0.4;
}