html,
body {
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
}

body {
    font-family: 'Montserrat', sans-serif;
    font-weight: 400;
    line-height: 1.5;
    height: 100vh;
}

strong {
    font-weight: 700;
}

.photo-frame {
    width: 100%;
    height: 100%;
    position: relative;
}

.photo {
    display: block;
    width: 100%;
    height: 100%;
    margin: 0;
    background-repeat: no-repeat;
    background-position: center center;
    background-size: cover;
    background-color: #333;
    transition: all 0.15s ease-in;
}

.photo.next {
    position: absolute;
    top: 0;
    left: 0;
    opacity: 0;
    transition: opacity 5s ease-out;
}

.photo.next.visible {
    opacity: 1;
}

footer {
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    z-index: 10;
    padding: 1rem 2.5rem;
    background-color: rgba(0, 0, 0, 0.5);
    color: #e0e0e0;
    font-weight: 700;
    text-align: right;
    transition: all 0.5s ease-in;
}

footer:hover {
    background-color: rgba(0, 0, 0, 0.9);
    color: #fff;
}

footer:hover + .photo-frame .photo {
    -webkit-filter: grayscale(100%) brightness(1.15);
    -moz-filter: grayscale(100%) brightness(1.15);
    -o-filter: grayscale(100%) brightness(1.15);
    -ms-filter: grayscale(100%) brightness(1.15);
    filter: grayscale(100%) brightness(1.15);
}

.portrait-hint {
    opacity: 0;
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    z-index: 10;
    padding: 1rem 2.5rem;
    background-color: rgba(0, 0, 0, 0.5);
    color: #fff;
    transition: opacity 0.5s ease-in-out;
}

@media only screen 
  and (min-device-width: 320px) 
  and (max-device-width: 736px)
  and (orientation: portrait) 
{
    .portrait-hint {
        opacity: 1;
    }   
}