* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Poppins', 'Noto Sans KR', sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    padding: 20px;
}

.container {
    max-width: 1400px;
    margin: 0 auto;
}

/* Header */
header {
    text-align: center;
    color: white;
    margin-bottom: 30px;
}

header h1 {
    font-size: 3rem;
    font-weight: 700;
    margin-bottom: 10px;
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.2);
}

header h1 i {
    color: #ffd700;
}

.subtitle {
    font-size: 1.2rem;
    opacity: 0.9;
}

/* Mode Switch */
.mode-switch {
    display: flex;
    justify-content: center;
    gap: 15px;
    margin-bottom: 30px;
}

.mode-btn {
    padding: 12px 30px;
    font-size: 1rem;
    font-weight: 600;
    border: none;
    border-radius: 50px;
    background: white;
    color: #667eea;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
}

.mode-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(0, 0, 0, 0.3);
}

.mode-btn.active {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
}

.mode-btn i {
    margin-right: 8px;
}

/* Grid Mode */
.grid-container {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 25px;
    padding: 20px 0;
}

/* Flashcard */
.flashcard {
    perspective: 1000px;
    height: 350px;
    cursor: pointer;
}

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

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

.flashcard-front,
.flashcard-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: 20px;
    box-shadow: 0 8px 30px rgba(0, 0, 0, 0.3);
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    padding: 30px;
}

.flashcard-front {
    background: white;
}

.flashcard-back {
    background: white;
    transform: rotateY(180deg);
}

.card-number {
    position: absolute;
    top: 15px;
    left: 20px;
    font-size: 0.9rem;
    font-weight: 600;
    padding: 5px 15px;
    border-radius: 20px;
    background: rgba(0, 0, 0, 0.1);
}

.card-phrase {
    font-size: 2.5rem;
    font-weight: 700;
    margin: 20px 0;
    color: #333;
}

.click-hint {
    font-size: 0.9rem;
    color: #666;
    margin-top: auto;
    display: flex;
    align-items: center;
    gap: 8px;
}

.click-hint i {
    font-size: 1.2rem;
    animation: bounce 2s infinite;
}

@keyframes bounce {
    0%, 100% { transform: translateY(0); }
    50% { transform: translateY(-10px); }
}

.card-description {
    font-size: 1.1rem;
    line-height: 1.8;
    color: #333;
    text-align: left;
}

/* Card Colors */
.flashcard:nth-child(10n+1) .flashcard-front { background: linear-gradient(135deg, #ffeaa7 0%, #fdcb6e 100%); }
.flashcard:nth-child(10n+2) .flashcard-front { background: linear-gradient(135deg, #a29bfe 0%, #6c5ce7 100%); }
.flashcard:nth-child(10n+3) .flashcard-front { background: linear-gradient(135deg, #fd79a8 0%, #e84393 100%); }
.flashcard:nth-child(10n+4) .flashcard-front { background: linear-gradient(135deg, #55efc4 0%, #00b894 100%); }
.flashcard:nth-child(10n+5) .flashcard-front { background: linear-gradient(135deg, #74b9ff 0%, #0984e3 100%); }
.flashcard:nth-child(10n+6) .flashcard-front { background: linear-gradient(135deg, #fab1a0 0%, #e17055 100%); }
.flashcard:nth-child(10n+7) .flashcard-front { background: linear-gradient(135deg, #ffeaa7 0%, #f39c12 100%); }
.flashcard:nth-child(10n+8) .flashcard-front { background: linear-gradient(135deg, #dfe6e9 0%, #74b9ff 100%); }
.flashcard:nth-child(10n+9) .flashcard-front { background: linear-gradient(135deg, #81ecec 0%, #00cec9 100%); }
.flashcard:nth-child(10n+10) .flashcard-front { background: linear-gradient(135deg, #a29bfe 0%, #fd79a8 100%); }

.flashcard:nth-child(10n+1) .flashcard-back { background: linear-gradient(135deg, #fff5e1 0%, #ffe4b5 100%); }
.flashcard:nth-child(10n+2) .flashcard-back { background: linear-gradient(135deg, #e8e6ff 0%, #dcd9ff 100%); }
.flashcard:nth-child(10n+3) .flashcard-back { background: linear-gradient(135deg, #ffe4f0 0%, #ffd6ea 100%); }
.flashcard:nth-child(10n+4) .flashcard-back { background: linear-gradient(135deg, #d5fef1 0%, #c3fae8 100%); }
.flashcard:nth-child(10n+5) .flashcard-back { background: linear-gradient(135deg, #e3f2ff 0%, #d6eaff 100%); }
.flashcard:nth-child(10n+6) .flashcard-back { background: linear-gradient(135deg, #ffe8e3 0%, #ffddd4 100%); }
.flashcard:nth-child(10n+7) .flashcard-back { background: linear-gradient(135deg, #fff9e6 0%, #ffedd6 100%); }
.flashcard:nth-child(10n+8) .flashcard-back { background: linear-gradient(135deg, #f0f4f8 0%, #e3f2ff 100%); }
.flashcard:nth-child(10n+9) .flashcard-back { background: linear-gradient(135deg, #e0f9f9 0%, #cef5f5 100%); }
.flashcard:nth-child(10n+10) .flashcard-back { background: linear-gradient(135deg, #f5e6ff 0%, #ffe6f5 100%); }

/* Slide Mode */
.slide-container {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 30px;
}

.slide-controls {
    display: flex;
    align-items: center;
    gap: 30px;
    background: white;
    padding: 15px 30px;
    border-radius: 50px;
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.2);
}

.nav-btn {
    width: 50px;
    height: 50px;
    border: none;
    border-radius: 50%;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    font-size: 1.5rem;
    cursor: pointer;
    transition: all 0.3s ease;
    display: flex;
    align-items: center;
    justify-content: center;
}

.nav-btn:hover {
    transform: scale(1.1);
    box-shadow: 0 4px 15px rgba(102, 126, 234, 0.5);
}

.nav-btn:disabled {
    background: #ddd;
    cursor: not-allowed;
    transform: scale(1);
}

.slide-counter {
    font-size: 1.5rem;
    font-weight: 700;
    color: #667eea;
    min-width: 100px;
    text-align: center;
}

.slide-card-wrapper {
    width: 100%;
    max-width: 600px;
}

.slide-card-wrapper .flashcard {
    height: 450px;
}

.keyboard-hint {
    color: white;
    font-size: 0.9rem;
    opacity: 0.8;
    display: flex;
    align-items: center;
    gap: 8px;
}

/* Responsive */
@media (max-width: 768px) {
    header h1 {
        font-size: 2rem;
    }

    .subtitle {
        font-size: 1rem;
    }

    .grid-container {
        grid-template-columns: 1fr;
        gap: 20px;
    }

    .flashcard {
        height: 300px;
    }

    .card-phrase {
        font-size: 2rem;
    }

    .card-description {
        font-size: 1rem;
    }

    .mode-btn {
        padding: 10px 20px;
        font-size: 0.9rem;
    }

    .slide-card-wrapper .flashcard {
        height: 400px;
    }

    .slide-controls {
        padding: 10px 20px;
        gap: 20px;
    }

    .nav-btn {
        width: 40px;
        height: 40px;
        font-size: 1.2rem;
    }

    .slide-counter {
        font-size: 1.2rem;
        min-width: 80px;
    }
}

@media (max-width: 480px) {
    header h1 {
        font-size: 1.5rem;
    }

    .card-phrase {
        font-size: 1.5rem;
    }

    .flashcard {
        height: 280px;
    }

    .slide-card-wrapper .flashcard {
        height: 350px;
    }
}