:root {
    --primary: #3d47fd;
    --secondary: #010e21;
    --accent: #ff6b6b;
    --light: #d9dee2;
    --dark: #1a1c03;
    --success: #51cf66;
    --shadow: rgba(0,0,0, 0.1);
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

body {
    background-color: #f5f7fa;
    color: var(--dark);
    line-height: 1.6;
}

header {
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    color: white;
    padding: 2rem 1rem;
    text-align: center;
    box-shadow: 0 4px 12px var(--shadow);
}

h1 {
    font-size: 2.5rem;
    margin-bottom: 0.5rem;
}

.subtitle {
    font-size: 1.2rem;
    opacity: 0.9;
    max-width: 800px;
    margin: 0 auto;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem 1rem;
}

.intro-section {
    background-color: white;
    border-radius: 10px;
    padding: 2rem;
    margin-bottom: 2rem;
    box-shadow: 0 4px 12px var(--shadow);
}

.cards-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 1.5rem;
    margin-bottom: 3rem;
}

.card {
    background-color: white;
    border-radius: 10px;
    overflow: hidden;
    box-shadow: 0 4px 12px var(--shadow);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
    cursor: pointer;
}

.card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 16px var(--shadow);
}

.card-front, .card-back {
    padding: 1.5rem;
}

.card-front {
    background-color: var(--primary);
    color: white;
    min-height: 150px;
    display: flex;
    flex-direction: column;
    justify-content: center;
}

.card-back {
    background-color: var(--light);
    color: var(--dark);
    display: none;
}

.card.active .card-back {
    display: block;
}

.card-number {
    font-size: 0.8rem;
    opacity: 0.8;
    margin-bottom: 0.5rem;
}

.card-question {
    font-size: 1.2rem;
    font-weight: 600;
    margin-bottom: 1rem;
}

.card-answer {
    font-size: 1rem;
    margin-bottom: 1rem;
}

.card-link {
    color: var(--primary);
    text-decoration: none;
    font-weight: 600;
    display: inline-flex;
    align-items: center;
}

.card-link:hover {
    text-decoration: underline;
}

.details-section {
    background-color: white;
    border-radius: 10px;
    padding: 2rem;
    box-shadow: 0 4px 12px var(--shadow);
    margin-bottom: 2rem;
}

.details-section h2 {
    color: var(--primary);
    margin-bottom: 1.5rem;
    padding-bottom: 0.5rem;
    border-bottom: 2px solid var(--light);
}

.details-section h3 {
    color: var(--secondary);
    margin: 1.5rem 0 0.5rem;
}

.details-section p {
    margin-bottom: 1rem;
}

.example {
    background-color: var(--light);
    padding: 1rem;
    border-left: 4px solid var(--accent);
    margin: 1rem 0;
    border-radius: 0 5px 5px 0;
}

.index-section {
    background-color: white;
    border-radius: 10px;
    padding: 2rem;
    box-shadow: 0 4px 12px var(--shadow);
}

.index-list {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
    gap: 1rem;
    list-style-type: none;
}

.index-list li {
    margin-bottom: 0.5rem;
}

.index-list a {
    color: var(--primary);
    text-decoration: none;
    display: flex;
    align-items: center;
    padding: 0.5rem;
    border-radius: 5px;
    transition: background-color 0.2s;
}

.index-list a:hover {
    background-color: var(--light);
    text-decoration: underline;
}

.index-list a::before {
    content: "→";
    margin-right: 0.5rem;
    color: var(--accent);
}

footer {
    background-color: var(--dark);
    color: white;
    text-align: center;
    padding: 2rem 1rem;
    margin-top: 3rem;
}

@media (max-width: 768px) {
    .cards-grid {
        grid-template-columns: 1fr;
    }
    
    h1 {
        font-size: 2rem;
    }
}