body {
    margin: 0;
    padding: 0;
    background: #000;
    color: #fff;
    font-family: Arial, sans-serif;
    background-image: url("https://source.unsplash.com/random/1920x1080/?siblings");
    background-size: cover;
    background-repeat: no-repeat;
}

.container {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    height: 100vh;
}

.countdown-title {
    font-size: 5em;
    margin-bottom: 20px;
    text-align: center;
    text-shadow: 4px 3px rgb(0,0,0,0.5);
}

.countdown-timer {
    display: flex;
    justify-content: center;
    gap: 20px;
    font-size: 3em;
    text-shadow: 2px 1px rgb(0,0,0,0.5);
}

.flip-card {
    width: 80px;
    height: 120px;
    perspective: 600px;
}

.flip-card-inner {
    position: relative;
    width: 100%;
    height: 100%;
    text-align: center;
    transition: transform 0.6s;
    transform-style: preserve-3d;
}

.flip-card-front,
.flip-card-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
}

.flip-card-front {
    background-color: transparent;
    color: #fff;
}

.flip-card-back {
    background-color: #000;
    color: #fff;
    transform: rotateX(180deg);
}

.unit {
    display: block;
    font-size: 0.5em;
    margin-top: 5px;
}

/* Additional styles for the split-flap effect */
.flip-card-back {
    display: flex;
    align-items: center;
    justify-content: center;
}

.flip-card-back span {
    display: inline-block;
    width: 100%;
    height: 100%;
    font-size: 6em;
    line-height: 1em;
    font-weight: bold;
}