:root {
    /* Colors */
    --bg-color: #F8F9FA;
    --text-primary: #1C1C1E;
    --text-secondary: #6B7280;
    --accent-blue: #007AFF;
    --card-bg: #FFFFFF;
    
    --success-bg: #DEF7EC;
    --success-text: #03543F;
    
    --error-bg: #FDE8E8;
    --error-text: #9B1C1C;
    
    --border-color: #E5E7EB;

    /* Spacing */
    --container-width: 1200px;
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2.5rem;
    
    /* Typography */
    --font-family: 'Inter', sans-serif;
}

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

body {
    font-family: var(--font-family);
    background-color: var(--bg-color);
    color: var(--text-primary);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

/* Layout */
.container {
    max-width: var(--container-width);
    margin: 0 auto;
    padding: var(--spacing-lg) var(--spacing-sm);
    min-height: 90vh;
    display: flex;
    flex-direction: column;
}

/* Hero Section */
.hero {
    text-align: center;
    margin-bottom: var(--spacing-lg);
    padding: var(--spacing-md) 0;
}

.hero h1 {
    font-size: 2.5rem;
    font-weight: 700;
    letter-spacing: -0.02em;
    margin-bottom: var(--spacing-xs);
    color: var(--text-primary);
}

.hero p {
    color: var(--text-secondary);
    font-size: 1.125rem;
}

/* Filters */
.filters {
    display: flex;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-lg);
    justify-content: center;
    flex-wrap: wrap;
}

.search-wrapper {
    position: relative;
    width: 100%;
    max-width: 400px;
}

.search-wrapper input {
    width: 100%;
    padding: 12px 16px 12px 48px;
    border: 1px solid var(--border-color);
    border-radius: 12px;
    font-size: 1rem;
    font-family: inherit;
    transition: all 0.2s ease;
    background: var(--card-bg);
}

.search-wrapper input:focus {
    outline: none;
    border-color: var(--accent-blue);
    box-shadow: 0 0 0 4px rgba(0, 122, 255, 0.1);
}

.search-icon {
    position: absolute;
    left: 16px;
    top: 50%;
    transform: translateY(-50%);
    color: var(--text-secondary);
    pointer-events: none;
}

.filter-wrapper select {
    appearance: none;
    padding: 12px 36px 12px 16px;
    border: 1px solid var(--border-color);
    border-radius: 12px;
    font-size: 1rem;
    font-family: inherit;
    background-color: var(--card-bg);
    cursor: pointer;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='24' height='24' viewBox='0 0 24 24' fill='none' stroke='%236B7280' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpolyline points='6 9 12 15 18 9'%3E%3C/polyline%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 8px center;
    background-size: 16px;
    transition: all 0.2s ease;
}

.filter-wrapper select:focus {
    outline: none;
    border-color: var(--accent-blue);
    box-shadow: 0 0 0 4px rgba(0, 122, 255, 0.1);
}

/* Book Grid */
.book-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--spacing-md);
    animation: fadeIn 0.4s ease-out;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Book Card */
.book-card {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    padding: var(--spacing-md);
    transition: transform 0.2s ease, box-shadow 0.2s ease;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    height: 180px;
}

.book-card:hover {
    transform: translateY(-4px);
    box-shadow: 0 12px 24px rgba(0,0,0,0.05);
    border-color: transparent;
}

.book-info h3 {
    font-size: 1.125rem;
    font-weight: 600;
    margin-bottom: 4px;
    line-height: 1.3;
}

.book-info .author {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.card-footer {
    display: flex;
    justify-content: flex-start;
    align-items: center;
    margin-top: var(--spacing-sm);
}

.badge {
    padding: 6px 12px;
    border-radius: 20px;
    font-size: 0.8rem;
    font-weight: 600;
    display: inline-flex;
    align-items: center;
    gap: 6px;
}

.badge.available {
    background-color: var(--success-bg);
    color: var(--success-text);
}

.badge.out-of-stock {
    background-color: var(--error-bg);
    color: var(--error-text);
}

/* Empty State */
.empty-state {
    text-align: center;
    padding: var(--spacing-lg) 0;
    color: var(--text-secondary);
}

.hidden {
    display: none;
}

.empty-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-sm);
}

/* Footer */
footer {
    text-align: center;
    padding: var(--spacing-md);
    color: var(--text-secondary);
    font-size: 0.875rem;
    border-top: 1px solid var(--border-color);
    margin-top: auto;
}

/* Responsive */
@media (max-width: 900px) {
    .book-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 600px) {
    .hero h1 {
        font-size: 2rem;
    }
    
    .filters {
        flex-direction: column;
        align-items: stretch;
    }

    .search-wrapper {
        max-width: 100%;
    }

    .book-grid {
        grid-template-columns: 1fr;
    }
    
    .book-card {
        height: auto;
        min-height: 160px;
    }
}