/* ============================================
   Student Book Manager - Stylesheet
   ============================================ */

@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&display=swap');

/* --- CSS Reset & Base --- */
*, *::before, *::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --primary: #6366f1;
    --primary-dark: #4f46e5;
    --primary-light: #818cf8;
    --secondary: #0ea5e9;
    --success: #10b981;
    --danger: #ef4444;
    --warning: #f59e0b;
    --bg-dark: #0f172a;
    --bg-card: #1e293b;
    --bg-input: #334155;
    --text-primary: #f1f5f9;
    --text-secondary: #94a3b8;
    --text-muted: #64748b;
    --border: #334155;
    --shadow: 0 4px 6px -1px rgba(0,0,0,0.3), 0 2px 4px -2px rgba(0,0,0,0.2);
    --shadow-lg: 0 10px 15px -3px rgba(0,0,0,0.4), 0 4px 6px -4px rgba(0,0,0,0.3);
    --radius: 12px;
    --radius-sm: 8px;
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

body {
    font-family: 'Inter', -apple-system, sans-serif;
    background: var(--bg-dark);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
}

/* --- Navigation --- */
.navbar {
    background: linear-gradient(135deg, var(--bg-card) 0%, #1a2332 100%);
    border-bottom: 1px solid var(--border);
    padding: 1rem 2rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
    position: sticky;
    top: 0;
    z-index: 100;
    backdrop-filter: blur(10px);
}

.navbar-brand {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
    text-decoration: none;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.navbar-brand span {
    background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.nav-links {
    display: flex;
    gap: 0.5rem;
    list-style: none;
}

.nav-links a {
    color: var(--text-secondary);
    text-decoration: none;
    padding: 0.6rem 1.2rem;
    border-radius: var(--radius-sm);
    font-weight: 500;
    font-size: 0.9rem;
    transition: var(--transition);
}

.nav-links a:hover,
.nav-links a.active {
    color: var(--text-primary);
    background: rgba(99, 102, 241, 0.15);
}

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

/* --- Page Header --- */
.page-header {
    margin-bottom: 2rem;
    display: flex;
    align-items: center;
    justify-content: space-between;
    flex-wrap: wrap;
    gap: 1rem;
}

.page-header h1 {
    font-size: 1.8rem;
    font-weight: 700;
    background: linear-gradient(135deg, var(--text-primary) 0%, var(--text-secondary) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

/* --- Cards --- */
.card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    overflow: hidden;
    transition: var(--transition);
}

.card:hover {
    box-shadow: var(--shadow-lg);
    border-color: rgba(99, 102, 241, 0.3);
}

.card-body {
    padding: 1.5rem;
}

/* --- Hero Section (Home) --- */
.hero {
    text-align: center;
    padding: 4rem 2rem;
}

.hero h1 {
    font-size: 3rem;
    font-weight: 800;
    margin-bottom: 1rem;
    background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 50%, var(--success) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero p {
    font-size: 1.2rem;
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto 2.5rem;
}

.hero-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.5rem;
    max-width: 900px;
    margin: 0 auto;
}

.hero-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 2rem;
    text-align: center;
    transition: var(--transition);
    text-decoration: none;
    color: inherit;
}

.hero-card:hover {
    transform: translateY(-4px);
    border-color: var(--primary);
    box-shadow: var(--shadow-lg), 0 0 30px rgba(99, 102, 241, 0.1);
}

.hero-card .icon {
    font-size: 2.5rem;
    margin-bottom: 1rem;
}

.hero-card h3 {
    font-size: 1.2rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
    color: var(--text-primary);
}

.hero-card p {
    font-size: 0.9rem;
    color: var(--text-muted);
    margin-bottom: 0;
}

/* --- Tables --- */
.table-wrapper {
    overflow-x: auto;
    border-radius: var(--radius);
    border: 1px solid var(--border);
}

table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.9rem;
}

thead {
    background: linear-gradient(135deg, rgba(99, 102, 241, 0.2) 0%, rgba(14, 165, 233, 0.15) 100%);
}

thead th {
    padding: 1rem 1.2rem;
    text-align: left;
    font-weight: 600;
    color: var(--text-primary);
    text-transform: uppercase;
    font-size: 0.75rem;
    letter-spacing: 0.05em;
    border-bottom: 1px solid var(--border);
}

tbody tr {
    transition: var(--transition);
    border-bottom: 1px solid rgba(51, 65, 85, 0.5);
}

tbody tr:hover {
    background: rgba(99, 102, 241, 0.08);
}

tbody tr:last-child {
    border-bottom: none;
}

tbody td {
    padding: 0.9rem 1.2rem;
    color: var(--text-secondary);
}

/* --- Buttons --- */
.btn {
    display: inline-flex;
    align-items: center;
    gap: 0.4rem;
    padding: 0.6rem 1.4rem;
    border: none;
    border-radius: var(--radius-sm);
    font-family: inherit;
    font-size: 0.9rem;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition);
    text-decoration: none;
    white-space: nowrap;
}

.btn-primary {
    background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
    color: white;
    box-shadow: 0 2px 8px rgba(99, 102, 241, 0.3);
}

.btn-primary:hover {
    transform: translateY(-1px);
    box-shadow: 0 4px 12px rgba(99, 102, 241, 0.5);
}

.btn-success {
    background: linear-gradient(135deg, var(--success) 0%, #059669 100%);
    color: white;
    box-shadow: 0 2px 8px rgba(16, 185, 129, 0.3);
}

.btn-success:hover {
    transform: translateY(-1px);
    box-shadow: 0 4px 12px rgba(16, 185, 129, 0.5);
}

.btn-warning {
    background: linear-gradient(135deg, var(--warning) 0%, #d97706 100%);
    color: white;
    box-shadow: 0 2px 8px rgba(245, 158, 11, 0.3);
}

.btn-warning:hover {
    transform: translateY(-1px);
}

.btn-secondary {
    background: var(--bg-input);
    color: var(--text-secondary);
    border: 1px solid var(--border);
}

.btn-secondary:hover {
    color: var(--text-primary);
    border-color: var(--text-muted);
}

.btn-sm {
    padding: 0.4rem 0.9rem;
    font-size: 0.8rem;
}

/* --- Forms --- */
.form-container {
    max-width: 600px;
    margin: 0 auto;
}

.form-group {
    margin-bottom: 1.5rem;
}

.form-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.form-control {
    width: 100%;
    padding: 0.75rem 1rem;
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    color: var(--text-primary);
    font-family: inherit;
    font-size: 0.95rem;
    transition: var(--transition);
    outline: none;
}

.form-control:focus {
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.2);
}

.form-control::placeholder {
    color: var(--text-muted);
}

select.form-control {
    appearance: none;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' fill='%2394a3b8' viewBox='0 0 16 16'%3E%3Cpath d='M8 11L3 6h10l-5 5z'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 1rem center;
    padding-right: 2.5rem;
}

.form-actions {
    display: flex;
    gap: 1rem;
    margin-top: 2rem;
}

/* --- Alerts --- */
.alert {
    padding: 1rem 1.2rem;
    border-radius: var(--radius-sm);
    margin-bottom: 1.5rem;
    font-size: 0.9rem;
    font-weight: 500;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    animation: slideIn 0.3s ease-out;
}

.alert-success {
    background: rgba(16, 185, 129, 0.15);
    border: 1px solid rgba(16, 185, 129, 0.3);
    color: var(--success);
}

.alert-error {
    background: rgba(239, 68, 68, 0.15);
    border: 1px solid rgba(239, 68, 68, 0.3);
    color: var(--danger);
}

/* --- Badge --- */
.badge {
    display: inline-block;
    padding: 0.2rem 0.6rem;
    border-radius: 20px;
    font-size: 0.75rem;
    font-weight: 600;
}

.badge-primary {
    background: rgba(99, 102, 241, 0.2);
    color: var(--primary-light);
}

.badge-secondary {
    background: rgba(14, 165, 233, 0.2);
    color: var(--secondary);
}

/* --- Empty State --- */
.empty-state {
    text-align: center;
    padding: 3rem;
    color: var(--text-muted);
}

.empty-state p {
    margin-bottom: 1rem;
    font-size: 1.1rem;
}

/* --- Footer --- */
.footer {
    text-align: center;
    padding: 2rem;
    margin-top: 3rem;
    border-top: 1px solid var(--border);
    color: var(--text-muted);
    font-size: 0.85rem;
}

/* --- Animations --- */
@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateY(-10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

.fade-in {
    animation: fadeIn 0.5s ease-out;
}

/* --- Responsive --- */
@media (max-width: 768px) {
    .navbar {
        flex-direction: column;
        gap: 1rem;
        padding: 1rem;
    }

    .nav-links {
        flex-wrap: wrap;
        justify-content: center;
    }

    .hero h1 {
        font-size: 2rem;
    }

    .container {
        padding: 1rem;
    }

    .page-header {
        flex-direction: column;
        align-items: flex-start;
    }

    .form-actions {
        flex-direction: column;
    }
}