:root {
    --card-size: 120px;
    --card-gap: 1rem;
    --card-border-radius: 12px;
    --flip-duration: 0.6s;
    --card-background: #FFFFFF;
    --card-back-bg: #f0f0f0;
    --text-color: #333333;
    --shadow: 0 4px 8px rgba(0,0,0,0.1);
}

.writing-systems {
    padding: 2rem;
    max-width: 1200px;
    margin: 0 auto;
}

.main-nav{
    background-color: rgb(0, 0, 0);
    height: 20px;
}

.tabs {
    display: flex;
    justify-content: center;
    gap: 1rem;
    margin-bottom: 2rem;
}

/* ...rest of your existing CSS... */


.tab-btn {
    padding: 0.8rem 1.5rem;
    border: none;
    border-radius: var(--border-radius);
    background: var(--card-background);
    cursor: pointer;
    font-weight: 600;
    transition: all 0.3s ease;
}

.tab-btn.active {
    background: var(--primary-color);
    color: white;
}

.character-grid {
    display: none;
}

.character-grid.active {
    display: block;
}

.grid-container {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(var(--card-size), 1fr));
    gap: var(--card-gap);
    padding: 1rem;
}

.character-card {
    width: 100%;
    height: var(--card-size);
    perspective: 1000px;
    cursor: pointer;
}

.card-inner {
    position: relative;
    width: 100%;
    height: 100%;
    transform-style: preserve-3d;
    transition: transform var(--flip-duration);
}

.character-card:hover .card-inner {
    transform: rotateY(15deg);
}

.character-card.flipped .card-inner {
    transform: rotateY(180deg);
}

.card-front,
.card-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: var(--card-border-radius);
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}

.card-front {
    background: var(--card-background);
    font-size: 2.5rem;
}

.card-back {
    background: var(--card-back-bg, #f0f0f0);
    transform: rotateY(180deg);
}

.character {
    font-size: 2.5rem;
    margin-bottom: 0.5rem;
}

.romanji {
    font-size: 1.2rem;
    color: var(--text-color);
}

@media (max-width: 768px) {
    :root {
        --card-size: 100px;
    }

    .grid-container {
        gap: 0.5rem;
    }
}

@media (max-width: 480px) {
    :root {
        --card-size: 80px;
    }

    .character {
        font-size: 2rem;
    }
}