.advent-calendar {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    background-color: #f2f2f2;
    padding: 30px;
    margin: 0 auto;
    max-width: 980px;
}
.advent-calendar .day-wrapper {
    display: flex;
    perspective: 1200px;
    transform-style: preserve-3d;
}

.advent-calendar .day {
    flex-grow: 1;
    transform-style: preserve-3d;
    transition: all 0.5s;
    position: relative;
    background: #eee;
    padding: 50%;
    text-align: center;
    cursor: pointer;
}

.advent-calendar .day-wrapper:hover .day:not(.locked):before {
    left: -1px;
    transform: perspective(1200px) translateZ(0px) translateX(0px) translateY(0px) rotateY(-105deg);
}

.advent-calendar .day-wrapper .day:before {
    content: attr(data-day);
    display: flex;
    align-items: center;
    justify-content: center;
    position: absolute;
    top: -2px;
    left: -2px;
    right: -2px;
    bottom: -2px;
    font-size: 30px;
    font-weight: bold;
    transform-style: preserve-3d;
    transform-origin: left center;
    background-color: inherit;
    transition: .5s ease;
    border: inherit;
}

.advent-calendar .day.locked {
    background: #ccc;
    cursor: not-allowed;
}

.advent-calendar .preview-text,
.advent-calendar .preview-image {
    display: flex;
    justify-content: center;
    align-items: center;
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    z-index: -1;
}

.advent-calendar .preview-text {
    padding: 10px;
    background-color: rgba(0,0,0,.3);
    font-size: 16px;
}

.advent-calendar .preview-image img {
    width: 100%;
    height: 100%;
    object-fit: cover;
}

.advent-calendar-popup-wrapper {
    display: flex;
    align-items: center;
    justify-content: center;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0,0,0,0.7);
    z-index: 9999;
}

.advent-calendar-popup {
    position: relative;
    background: #fff;
    padding: 60px 30px 30px 30px;
    min-width: 320px;
    max-width: 800px;
    max-height: 80vh;
    overflow: auto;
}

.advent-calendar-popup-close {
    position:absolute;
    top: 15px;
    right: 15px;
    cursor: pointer;
    border: none;
    background: transparent;
    font-size: 30px;
}

@media screen and (min-width: 992px) {
    .advent-calendar {
        grid-template-columns: repeat(6, 1fr);
    }
}