/* ==========================================================================
   Design System & Variable Definitions
   ========================================================================== */
:root {
    /* Color Palette */
    --primary-color: #002147;       /* Kyoto University Dark Blue */
    --primary-light: #1e3d59;
    --primary-rgb: 0, 33, 71;
    --accent-color: #d4af37;        /* Gold / Ochre Accent */
    --accent-hover: #c5a028;
    --accent-rgb: 212, 175, 55;
    
    --success-color: #2a9d8f;       /* Emerald Green */
    --warning-color: #f4a261;       /* Warm Orange */
    --danger-color: #e76f51;        /* Terracotta */
    --info-color: #4a90e2;          /* Sky Blue */

    /* Light Theme (Default) */
    --bg-color: #f5f7fa;
    --card-bg: #ffffff;
    --card-border: rgba(0, 0, 0, 0.06);
    --text-color: #2b2d42;
    --text-secondary: #6c757d;
    --border-color: #e9ecef;
    --input-bg: #ffffff;
    --input-border: #ced4da;
    
    /* Layout & Shadow */
    --header-height: 70px;
    --mobile-nav-height: 60px;
    --border-radius-sm: 8px;
    --border-radius-md: 12px;
    --border-radius-lg: 20px;
    
    --shadow-sm: 0 2px 4px rgba(0, 0, 0, 0.04);
    --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.08);
    --shadow-lg: 0 10px 30px rgba(0, 0, 0, 0.12);
    --glass-bg: rgba(255, 255, 255, 0.85);
    --glass-backdrop: blur(10px);

    /* Transitions */
    --transition-fast: 0.15s ease;
    --transition-normal: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}

/* System Dark Mode Auto-switch */
@media (prefers-color-scheme: dark) {
    :root {
        --bg-color: #0b0f19;
        --card-bg: #161c2a;
        --card-border: rgba(255, 255, 255, 0.05);
        --text-color: #f3f4f6;
        --text-secondary: #9ca3af;
        --border-color: #242f41;
        --input-bg: #1f293d;
        --input-border: #374151;
        --glass-bg: rgba(22, 28, 42, 0.85);
        --shadow-md: 0 4px 20px rgba(0, 0, 0, 0.3);
        --shadow-lg: 0 12px 40px rgba(0, 0, 0, 0.5);
    }
}

/* ==========================================================================
   Basic Resets & Typography
   ========================================================================== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    -webkit-tap-highlight-color: transparent;
}

body {
    font-family: 'Inter', 'Noto Sans JP', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    transition: background-color var(--transition-normal), color var(--transition-normal);
    overflow-x: hidden;
}

a {
    color: var(--primary-light);
    text-decoration: none;
    transition: color var(--transition-fast);
}
@media (prefers-color-scheme: dark) {
    a {
        color: #64b5f6;
    }
}
a:hover {
    color: var(--accent-color);
    text-decoration: underline;
}

button {
    font-family: inherit;
    border: none;
    background: none;
    cursor: pointer;
    outline: none;
}

img {
    max-width: 100%;
    height: auto;
    display: block;
}

/* Scrollbar styling */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}
::-webkit-scrollbar-track {
    background: var(--bg-color);
}
::-webkit-scrollbar-thumb {
    background: var(--border-color);
    border-radius: 4px;
}
::-webkit-scrollbar-thumb:hover {
    background: var(--text-secondary);
}

/* ==========================================================================
   Layout Structure
   ========================================================================== */
#app {
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

/* Header & Nav */
.app-header {
    height: var(--header-height);
    background-color: var(--glass-bg);
    backdrop-filter: var(--glass-backdrop);
    border-bottom: 1px solid var(--border-color);
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: var(--shadow-sm);
    transition: background-color var(--transition-normal), border-color var(--transition-normal);
}

.header-container {
    max-width: 1200px;
    height: 100%;
    margin: 0 auto;
    padding: 0 20px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 20px;
}

.brand {
    display: flex;
    align-items: center;
    gap: 12px;
    cursor: pointer;
}

.logo-img {
    height: 42px;
    width: 42px;
    object-fit: contain;
    border-radius: 50%;
    border: 2px solid var(--accent-color);
    box-shadow: var(--shadow-sm);
}

.brand-text {
    display: flex;
    flex-direction: column;
}

.brand-title {
    font-family: 'Outfit', sans-serif;
    font-size: 20px;
    font-weight: 800;
    color: var(--primary-color);
    letter-spacing: -0.5px;
    line-height: 1.2;
}
@media (prefers-color-scheme: dark) {
    .brand-title {
        color: #ffffff;
    }
}

.brand-badge {
    font-size: 10px;
    font-weight: 700;
    background-color: var(--primary-color);
    color: #ffffff;
    padding: 1px 6px;
    border-radius: 4px;
    width: fit-content;
    margin-top: 2px;
    letter-spacing: 0.5px;
    border: 1px solid rgba(255,255,255,0.1);
}
@media (prefers-color-scheme: dark) {
    .brand-badge {
        background-color: var(--accent-color);
        color: #0b0f19;
        border: none;
    }
}

/* Header Search */
.header-search-container {
    flex: 1;
    max-width: 480px;
    display: block;
}

.search-bar {
    position: relative;
    width: 100%;
}

.search-icon {
    position: absolute;
    left: 14px;
    top: 50%;
    transform: translateY(-50%);
    color: var(--text-secondary);
    font-size: 14px;
}

.search-bar input {
    width: 100%;
    height: 40px;
    padding: 0 16px 0 40px;
    background-color: var(--input-bg);
    border: 1.5px solid var(--input-border);
    border-radius: var(--border-radius-lg);
    color: var(--text-color);
    font-size: 14px;
    outline: none;
    transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.search-bar input:focus {
    border-color: var(--primary-light);
    box-shadow: 0 0 0 3px rgba(var(--primary-rgb), 0.15);
}
@media (prefers-color-scheme: dark) {
    .search-bar input:focus {
        border-color: var(--accent-color);
        box-shadow: 0 0 0 3px rgba(var(--accent-rgb), 0.2);
    }
}

.mobile-search-wrapper {
    display: none;
    padding: 10px 16px;
    background-color: var(--card-bg);
    border-bottom: 1px solid var(--border-color);
}

/* Desktop Nav Menu */
.nav-menu {
    display: flex;
    align-items: center;
    gap: 8px;
}

.nav-item {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 8px 16px;
    border-radius: var(--border-radius-md);
    color: var(--text-secondary);
    font-weight: 500;
    font-size: 14px;
    transition: all var(--transition-fast);
}

.nav-item i {
    font-size: 16px;
}

.nav-item:hover {
    color: var(--primary-color);
    background-color: rgba(var(--primary-rgb), 0.05);
}
@media (prefers-color-scheme: dark) {
    .nav-item:hover {
        color: #ffffff;
        background-color: rgba(255, 255, 255, 0.05);
    }
}

.nav-item.active {
    color: var(--primary-color);
    background-color: rgba(var(--primary-rgb), 0.08);
    font-weight: 600;
}
@media (prefers-color-scheme: dark) {
    .nav-item.active {
        color: var(--accent-color);
        background-color: rgba(var(--accent-rgb), 0.15);
    }
}

.nav-badge {
    color: var(--danger-color);
    font-size: 8px;
    margin-left: -2px;
}

/* Wallet Display */
.wallet-balance {
    display: flex;
    flex-direction: column;
    align-items: flex-end;
    padding: 4px 12px;
    border-radius: var(--border-radius-sm);
    background: linear-gradient(135deg, var(--primary-color) 0%, var(--primary-light) 100%);
    color: #ffffff;
    min-width: 90px;
    box-shadow: var(--shadow-sm);
}
@media (prefers-color-scheme: dark) {
    .wallet-balance {
        background: linear-gradient(135deg, #1f293d 0%, #111827 100%);
        border: 1px solid rgba(255, 255, 255, 0.05);
    }
}

.wallet-label {
    font-size: 9px;
    text-transform: uppercase;
    opacity: 0.8;
}

.wallet-amount {
    font-family: 'Outfit', sans-serif;
    font-weight: 700;
    font-size: 14px;
}

/* Main content */
.app-main {
    flex: 1;
    max-width: 1200px;
    width: 100%;
    margin: 0 auto;
    padding: 24px 20px 48px;
}

/* Mobile Bottom Nav */
.mobile-bottom-nav {
    display: none;
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    height: var(--mobile-nav-height);
    background-color: var(--glass-bg);
    backdrop-filter: var(--glass-backdrop);
    border-top: 1px solid var(--border-color);
    z-index: 100;
    box-shadow: 0 -2px 10px rgba(0, 0, 0, 0.04);
}

.mobile-nav-item {
    flex: 1;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    color: var(--text-secondary);
    font-size: 10px;
    gap: 4px;
    transition: color var(--transition-fast);
}

.mobile-nav-item i {
    font-size: 18px;
}

.mobile-nav-item.active {
    color: var(--primary-color);
}
@media (prefers-color-scheme: dark) {
    .mobile-nav-item.active {
        color: var(--accent-color);
    }
}

.mobile-badge {
    position: absolute;
    top: 8px;
    right: 25%;
    width: 8px;
    height: 8px;
    border-radius: 50%;
    background-color: var(--danger-color);
}

/* Footer styling */
.app-footer {
    background-color: var(--primary-color);
    color: rgba(255, 255, 255, 0.8);
    padding: 40px 20px;
    margin-top: auto;
    border-top: 3px solid var(--accent-color);
}
@media (prefers-color-scheme: dark) {
    .app-footer {
        background-color: #080b11;
        color: var(--text-secondary);
        border-top: 1px solid var(--border-color);
    }
}

.footer-container {
    max-width: 1200px;
    margin: 0 auto;
    display: grid;
    grid-template-columns: 2fr 1fr;
    gap: 40px;
}

.footer-info h3 {
    color: #ffffff;
    font-family: 'Outfit', sans-serif;
    margin-bottom: 12px;
}

.footer-links h4 {
    color: #ffffff;
    margin-bottom: 12px;
}

.footer-links ul {
    list-style: none;
}

.footer-links li {
    margin-bottom: 8px;
}

.footer-links a {
    color: rgba(255,255,255,0.7);
}
@media (prefers-color-scheme: dark) {
    .footer-links a {
        color: var(--text-secondary);
    }
}

.footer-links a:hover {
    color: var(--accent-color);
}

.footer-disclaimer {
    grid-column: 1 / span 2;
    border-top: 1px solid rgba(255,255,255,0.1);
    padding-top: 20px;
    font-size: 12px;
    text-align: center;
}

/* ==========================================================================
   Home View: Hero, Category, Books Grid
   ========================================================================== */
.hero-section {
    background: linear-gradient(135deg, rgba(var(--primary-rgb), 0.9) 0%, rgba(var(--primary-rgb), 0.7) 100%), url('data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" width="100" height="100" viewBox="0 0 100 100"><rect fill="%23002147" opacity="0.05" width="100" height="100"/><circle fill="%23ffffff" opacity="0.02" cx="50" cy="50" r="40"/></svg>');
    background-size: cover;
    color: #ffffff;
    padding: 50px 40px;
    border-radius: var(--border-radius-lg);
    box-shadow: var(--shadow-md);
    position: relative;
    overflow: hidden;
    margin-bottom: 40px;
}
@media (prefers-color-scheme: dark) {
    .hero-section {
        background: linear-gradient(135deg, #161c2a 0%, #0b0f19 100%);
        border: 1px solid var(--border-color);
    }
}

.hero-content {
    max-width: 600px;
    position: relative;
    z-index: 2;
}

.hero-section::after {
    content: '';
    position: absolute;
    right: -50px;
    bottom: -50px;
    width: 250px;
    height: 250px;
    background-color: var(--accent-color);
    opacity: 0.1;
    border-radius: 50%;
}

.hero-tag {
    background-color: rgba(var(--accent-rgb), 0.2);
    border: 1px solid var(--accent-color);
    color: var(--accent-color);
    padding: 4px 12px;
    border-radius: var(--border-radius-sm);
    font-size: 12px;
    font-weight: 700;
    display: inline-block;
    margin-bottom: 16px;
    text-transform: uppercase;
}

.hero-title {
    font-size: 32px;
    font-weight: 800;
    line-height: 1.2;
    margin-bottom: 12px;
    font-family: 'Outfit', sans-serif;
}

.hero-subtitle {
    font-size: 16px;
    opacity: 0.9;
    margin-bottom: 24px;
}

.hero-stats {
    display: flex;
    gap: 30px;
}

.stat-item {
    display: flex;
    flex-direction: column;
}

.stat-val {
    font-family: 'Outfit', sans-serif;
    font-size: 24px;
    font-weight: 700;
    color: var(--accent-color);
}

.stat-label {
    font-size: 12px;
    opacity: 0.8;
}

/* Category Filters */
.section-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
}

.section-header h2 {
    font-size: 22px;
    font-weight: 700;
    color: var(--primary-color);
}
@media (prefers-color-scheme: dark) {
    .section-header h2 {
        color: #ffffff;
    }
}

.category-tags {
    display: flex;
    gap: 10px;
    overflow-x: auto;
    padding-bottom: 10px;
    margin-bottom: 30px;
    scrollbar-width: none;
}
.category-tags::-webkit-scrollbar {
    display: none;
}

.category-btn {
    padding: 8px 18px;
    background-color: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-lg);
    color: var(--text-color);
    font-size: 13px;
    font-weight: 500;
    white-space: nowrap;
    transition: all var(--transition-fast);
    box-shadow: var(--shadow-sm);
}

.category-btn:hover {
    border-color: var(--primary-light);
    color: var(--primary-color);
}
@media (prefers-color-scheme: dark) {
    .category-btn:hover {
        border-color: var(--accent-color);
        color: #ffffff;
    }
}

.category-btn.active {
    background-color: var(--primary-color);
    color: #ffffff;
    border-color: var(--primary-color);
}
@media (prefers-color-scheme: dark) {
    .category-btn.active {
        background-color: var(--accent-color);
        color: #0b0f19;
        border-color: var(--accent-color);
    }
}

/* Books Grid */
.books-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
    gap: 24px;
}

.no-results {
    grid-column: 1 / -1;
    text-align: center;
    padding: 50px 20px;
    background-color: var(--card-bg);
    border-radius: var(--border-radius-md);
    border: 1px solid var(--border-color);
}

.no-results i {
    font-size: 48px;
    color: var(--text-secondary);
    margin-bottom: 16px;
}

/* Textbook Card */
.book-card {
    background-color: var(--card-bg);
    border: 1.5px solid var(--card-border);
    border-radius: var(--border-radius-md);
    overflow: hidden;
    display: flex;
    flex-direction: column;
    transition: all var(--transition-normal);
    position: relative;
    box-shadow: var(--shadow-sm);
}

.book-card:hover {
    transform: translateY(-6px);
    border-color: rgba(var(--primary-rgb), 0.2);
    box-shadow: var(--shadow-md);
}
@media (prefers-color-scheme: dark) {
    .book-card:hover {
        border-color: var(--accent-color);
    }
}

.card-img-wrapper {
    aspect-ratio: 3/4;
    background-color: var(--border-color);
    position: relative;
    overflow: hidden;
    display: flex;
    align-items: center;
    justify-content: center;
}

.card-img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: transform var(--transition-normal);
}

.book-card:hover .card-img {
    transform: scale(1.05);
}

.status-badge {
    position: absolute;
    top: 10px;
    left: 10px;
    padding: 4px 8px;
    border-radius: var(--border-radius-sm);
    font-size: 11px;
    font-weight: 700;
    color: #ffffff;
    box-shadow: var(--shadow-sm);
    z-index: 2;
}

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

.status-badge.trading {
    background-color: var(--warning-color);
}

.status-badge.sold {
    background-color: var(--danger-color);
}

.faculty-tag {
    position: absolute;
    top: 10px;
    right: 10px;
    padding: 3px 8px;
    border-radius: var(--border-radius-sm);
    font-size: 10px;
    font-weight: 500;
    background-color: rgba(0, 0, 0, 0.6);
    color: #ffffff;
    backdrop-filter: blur(4px);
    z-index: 2;
}

.card-info {
    padding: 16px;
    display: flex;
    flex-direction: column;
    flex: 1;
}

.lecture-name {
    font-size: 11px;
    font-weight: 700;
    color: var(--primary-light);
    margin-bottom: 4px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}
@media (prefers-color-scheme: dark) {
    .lecture-name {
        color: var(--accent-color);
    }
}

.book-title {
    font-size: 15px;
    font-weight: 600;
    line-height: 1.3;
    margin-bottom: 8px;
    height: 40px;
    overflow: hidden;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
}

.book-meta {
    font-size: 12px;
    color: var(--text-secondary);
    margin-bottom: auto;
}

.card-footer {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-top: 12px;
    padding-top: 12px;
    border-top: 1px solid var(--border-color);
}

.price-display {
    font-family: 'Outfit', sans-serif;
    font-size: 18px;
    font-weight: 700;
    color: var(--text-color);
}

.condition-pill {
    padding: 2px 8px;
    border-radius: var(--border-radius-sm);
    font-size: 10px;
    font-weight: 600;
    background-color: var(--border-color);
    color: var(--text-secondary);
}

/* ==========================================================================
   Details View
   ========================================================================== */
.back-btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    font-size: 14px;
    font-weight: 600;
    color: var(--text-secondary);
    margin-bottom: 20px;
    transition: color var(--transition-fast);
}

.back-btn:hover {
    color: var(--primary-color);
}

.details-wrapper {
    display: grid;
    grid-template-columns: 1fr 1.2fr;
    gap: 40px;
    background-color: var(--card-bg);
    border-radius: var(--border-radius-lg);
    border: 1px solid var(--border-color);
    padding: 30px;
    box-shadow: var(--shadow-md);
}

.details-gallery {
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.details-img-main {
    border-radius: var(--border-radius-md);
    overflow: hidden;
    border: 1px solid var(--border-color);
    aspect-ratio: 3/4;
}

.details-img-main img {
    width: 100%;
    height: 100%;
    object-fit: cover;
}

.spot-map-preview {
    background-color: var(--bg-color);
    border-radius: var(--border-radius-md);
    padding: 16px;
    border: 1.5px dashed var(--border-color);
    display: flex;
    align-items: center;
    gap: 12px;
}

.spot-map-preview i {
    font-size: 24px;
    color: var(--danger-color);
}

.spot-details h4 {
    font-size: 13px;
    font-weight: 700;
}

.spot-details p {
    font-size: 11px;
    color: var(--text-secondary);
}

.details-content {
    display: flex;
    flex-direction: column;
}

.details-header {
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 20px;
    margin-bottom: 20px;
}

.details-tag-row {
    display: flex;
    gap: 8px;
    margin-bottom: 10px;
}

.details-title {
    font-size: 26px;
    font-weight: 700;
    line-height: 1.3;
    margin-bottom: 8px;
}

.details-author {
    color: var(--text-secondary);
    font-size: 14px;
}

.details-price-row {
    display: flex;
    align-items: center;
    gap: 20px;
    margin-bottom: 24px;
}

.details-price {
    font-family: 'Outfit', sans-serif;
    font-size: 32px;
    font-weight: 800;
    color: var(--primary-color);
}
@media (prefers-color-scheme: dark) {
    .details-price {
        color: #ffffff;
    }
}

/* Action buttons */
.btn-primary {
    background-color: var(--primary-color);
    color: #ffffff;
    padding: 14px 28px;
    border-radius: var(--border-radius-md);
    font-size: 16px;
    font-weight: 700;
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 10px;
    width: 100%;
    transition: all var(--transition-fast);
    box-shadow: var(--shadow-sm);
}

.btn-primary:hover {
    background-color: var(--primary-light);
    box-shadow: var(--shadow-md);
}
@media (prefers-color-scheme: dark) {
    .btn-primary {
        background-color: var(--accent-color);
        color: #0b0f19;
    }
    .btn-primary:hover {
        background-color: var(--accent-hover);
    }
}

.btn-primary:disabled {
    background-color: var(--border-color);
    color: var(--text-secondary);
    cursor: not-allowed;
    box-shadow: none;
}

/* Detail Table */
.spec-table {
    margin-top: 30px;
    border-collapse: collapse;
    width: 100%;
}

.spec-table tr {
    border-bottom: 1px solid var(--border-color);
}

.spec-table td {
    padding: 12px 0;
    font-size: 14px;
}

.spec-label {
    font-weight: 600;
    width: 30%;
    color: var(--text-secondary);
}

.spec-val {
    color: var(--text-color);
}

/* Seller Bio */
.seller-card {
    display: flex;
    align-items: center;
    gap: 16px;
    margin-top: 24px;
    padding: 16px;
    background-color: var(--bg-color);
    border-radius: var(--border-radius-md);
    border: 1px solid var(--border-color);
}

.seller-avatar {
    width: 48px;
    height: 48px;
    border-radius: 50%;
    background-color: var(--primary-color);
    color: #ffffff;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 20px;
    font-weight: 700;
}
@media (prefers-color-scheme: dark) {
    .seller-avatar {
        background-color: var(--accent-color);
        color: #0b0f19;
    }
}

.seller-info h4 {
    font-size: 14px;
    font-weight: 700;
}

.seller-info p {
    font-size: 12px;
    color: var(--text-secondary);
}

/* ==========================================================================
   Checkout View
   ========================================================================== */
.checkout-container {
    max-width: 800px;
    margin: 0 auto;
    background-color: var(--card-bg);
    border-radius: var(--border-radius-lg);
    border: 1px solid var(--border-color);
    padding: 30px;
    box-shadow: var(--shadow-md);
}

.checkout-title {
    font-size: 24px;
    font-weight: 700;
    margin-bottom: 24px;
    text-align: center;
    border-bottom: 1.5px solid var(--border-color);
    padding-bottom: 15px;
}

.checkout-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: 24px;
}

.item-summary {
    display: flex;
    gap: 20px;
    padding: 16px;
    background-color: var(--bg-color);
    border-radius: var(--border-radius-md);
    border: 1px solid var(--border-color);
}

.item-summary-img {
    width: 60px;
    height: 80px;
    object-fit: cover;
    border-radius: var(--border-radius-sm);
}

.item-summary-info {
    display: flex;
    flex-direction: column;
    justify-content: center;
}

.item-summary-title {
    font-weight: 600;
    font-size: 16px;
}

.item-summary-price {
    font-weight: 700;
    color: var(--primary-color);
    margin-top: 4px;
}
@media (prefers-color-scheme: dark) {
    .item-summary-price {
        color: var(--accent-color);
    }
}

/* Card Mock Form */
.payment-section {
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-md);
    padding: 24px;
}

.payment-title {
    font-size: 16px;
    font-weight: 700;
    margin-bottom: 16px;
    display: flex;
    align-items: center;
    gap: 8px;
}

.mock-card {
    background: linear-gradient(135deg, #1f293d 0%, #111827 100%);
    border: 1px solid rgba(255, 255, 255, 0.1);
    border-radius: var(--border-radius-md);
    padding: 20px;
    color: #ffffff;
    box-shadow: var(--shadow-md);
    margin-bottom: 24px;
    position: relative;
    overflow: hidden;
}

.mock-card::before {
    content: '';
    position: absolute;
    width: 200px;
    height: 200px;
    border-radius: 50%;
    background: rgba(255,255,255,0.03);
    top: -50px;
    right: -50px;
}

.card-logo {
    display: flex;
    justify-content: space-between;
    margin-bottom: 30px;
}

.card-logo span {
    font-family: 'Outfit', sans-serif;
    font-weight: 800;
    font-style: italic;
    opacity: 0.8;
}

.card-chip {
    width: 40px;
    height: 30px;
    background-color: var(--accent-color);
    border-radius: var(--border-radius-sm);
    opacity: 0.6;
}

.card-number-display {
    font-family: 'Outfit', sans-serif;
    font-size: 20px;
    letter-spacing: 2px;
    margin-bottom: 20px;
    text-shadow: 0 2px 4px rgba(0,0,0,0.5);
}

.card-meta-display {
    display: flex;
    justify-content: space-between;
    font-size: 12px;
    opacity: 0.8;
}

.form-group {
    margin-bottom: 16px;
}

.form-group label {
    display: block;
    font-size: 12px;
    font-weight: 600;
    margin-bottom: 6px;
    color: var(--text-secondary);
}

.form-group input, .form-group select, .form-group textarea {
    width: 100%;
    padding: 10px 14px;
    border-radius: var(--border-radius-sm);
    background-color: var(--input-bg);
    border: 1.5px solid var(--input-border);
    color: var(--text-color);
    font-size: 14px;
    outline: none;
    transition: all var(--transition-fast);
}

.form-group input:focus, .form-group select:focus, .form-group textarea:focus {
    border-color: var(--primary-color);
}
@media (prefers-color-scheme: dark) {
    .form-group input:focus, .form-group select:focus, .form-group textarea:focus {
        border-color: var(--accent-color);
    }
}

.form-row-2 {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
}

/* ==========================================================================
   Chat View (Trade Flow)
   ========================================================================== */
.chat-container {
    display: grid;
    grid-template-columns: 1.2fr 2fr;
    gap: 20px;
    height: calc(100vh - var(--header-height) - 100px);
}

@media (max-width: 768px) {
    .chat-container {
        grid-template-columns: 1fr;
        height: calc(100vh - var(--header-height) - var(--mobile-nav-height) - 30px);
    }
    .chat-sidebar {
        display: none; /* JS toggles back and forth on mobile */
    }
}

.chat-sidebar {
    background-color: var(--card-bg);
    border-radius: var(--border-radius-md);
    border: 1px solid var(--border-color);
    padding: 16px;
    display: flex;
    flex-direction: column;
    gap: 16px;
    overflow-y: auto;
}

.trade-details-sidebar {
    display: flex;
    flex-direction: column;
    gap: 14px;
}

.trade-book-info {
    display: flex;
    gap: 12px;
}

.trade-book-img {
    width: 50px;
    height: 66px;
    object-fit: cover;
    border-radius: var(--border-radius-sm);
}

.trade-book-meta h3 {
    font-size: 14px;
    font-weight: 700;
}

.trade-book-meta p {
    font-size: 11px;
    color: var(--text-secondary);
}

.trade-step-tracker {
    border-top: 1px solid var(--border-color);
    padding-top: 16px;
}

.step-item {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 16px;
    opacity: 0.5;
}

.step-item.active {
    opacity: 1;
}

.step-item.completed {
    opacity: 1;
}

.step-icon {
    width: 24px;
    height: 24px;
    border-radius: 50%;
    background-color: var(--border-color);
    color: var(--text-secondary);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 11px;
    font-weight: 700;
}

.step-item.active .step-icon {
    background-color: var(--primary-color);
    color: #ffffff;
}
@media (prefers-color-scheme: dark) {
    .step-item.active .step-icon {
        background-color: var(--accent-color);
        color: #0b0f19;
    }
}

.step-item.completed .step-icon {
    background-color: var(--success-color);
    color: #ffffff;
}

.step-text h4 {
    font-size: 13px;
    font-weight: 600;
}

.step-text p {
    font-size: 10px;
    color: var(--text-secondary);
}

/* Chat Main Panel */
.chat-main {
    background-color: var(--card-bg);
    border-radius: var(--border-radius-md);
    border: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

.chat-header {
    padding: 16px 20px;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.chat-partner {
    display: flex;
    align-items: center;
    gap: 12px;
}

.partner-avatar {
    width: 36px;
    height: 36px;
    border-radius: 50%;
    background-color: var(--primary-light);
    color: #ffffff;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    font-size: 14px;
}

.partner-info h3 {
    font-size: 14px;
    font-weight: 700;
}

.partner-info p {
    font-size: 11px;
    color: var(--text-secondary);
}

/* Control area (actions based on trade step) */
.trade-actions-bar {
    background-color: rgba(var(--primary-rgb), 0.03);
    border-bottom: 1px solid var(--border-color);
    padding: 12px 20px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 20px;
}

.action-status-text {
    font-size: 13px;
    font-weight: 600;
}

.chat-messages {
    flex: 1;
    overflow-y: auto;
    padding: 20px;
    display: flex;
    flex-direction: column;
    gap: 16px;
    background-color: rgba(var(--primary-rgb), 0.01);
}

/* Message Bubbles */
.message {
    display: flex;
    flex-direction: column;
    max-width: 70%;
}

.message.incoming {
    align-self: flex-start;
}

.message.outgoing {
    align-self: flex-end;
}

.message-bubble {
    padding: 10px 16px;
    border-radius: var(--border-radius-md);
    font-size: 14px;
    box-shadow: var(--shadow-sm);
    white-space: pre-wrap;
}

.message.incoming .message-bubble {
    background-color: var(--border-color);
    color: var(--text-color);
    border-top-left-radius: 0;
}

.message.outgoing .message-bubble {
    background-color: var(--primary-color);
    color: #ffffff;
    border-top-right-radius: 0;
}
@media (prefers-color-scheme: dark) {
    .message.outgoing .message-bubble {
        background-color: var(--primary-light);
    }
}

.message-time {
    font-size: 9px;
    color: var(--text-secondary);
    margin-top: 4px;
    align-self: flex-end;
}

.message.incoming .message-time {
    align-self: flex-start;
}

/* Specialized message type: Promise Offer */
.system-card-message {
    align-self: center;
    max-width: 90%;
    background-color: var(--card-bg);
    border: 1.5px solid var(--border-color);
    border-radius: var(--border-radius-md);
    padding: 16px;
    text-align: center;
    box-shadow: var(--shadow-sm);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 8px;
}

.system-card-title {
    font-size: 13px;
    font-weight: 700;
    color: var(--primary-color);
}
@media (prefers-color-scheme: dark) {
    .system-card-title {
        color: var(--accent-color);
    }
}

.system-card-body {
    font-size: 12px;
}

.system-card-buttons {
    display: flex;
    gap: 10px;
    margin-top: 8px;
}

.btn-sm-primary {
    background-color: var(--primary-color);
    color: #ffffff;
    padding: 6px 16px;
    border-radius: var(--border-radius-sm);
    font-size: 11px;
    font-weight: 600;
}
@media (prefers-color-scheme: dark) {
    .btn-sm-primary {
        background-color: var(--accent-color);
        color: #0b0f19;
    }
}

.btn-sm-secondary {
    background-color: var(--border-color);
    color: var(--text-color);
    padding: 6px 16px;
    border-radius: var(--border-radius-sm);
    font-size: 11px;
    font-weight: 600;
}

/* Chat Input Area */
.chat-input-bar {
    padding: 16px 20px;
    border-top: 1px solid var(--border-color);
    display: flex;
    gap: 12px;
    align-items: center;
}

.chat-input-bar textarea {
    flex: 1;
    height: 40px;
    resize: none;
    padding: 10px 14px;
    border-radius: var(--border-radius-lg);
    background-color: var(--input-bg);
    border: 1.5px solid var(--input-border);
    color: var(--text-color);
    outline: none;
    font-size: 14px;
    font-family: inherit;
    line-height: 1.2;
}

.chat-send-btn {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    background-color: var(--primary-color);
    color: #ffffff;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: background-color var(--transition-fast);
}
@media (prefers-color-scheme: dark) {
    .chat-send-btn {
        background-color: var(--accent-color);
        color: #0b0f19;
    }
}

.chat-send-btn:hover {
    opacity: 0.9;
}

/* ==========================================================================
   Sell View (Listing Form)
   ========================================================================== */
.sell-container {
    max-width: 800px;
    margin: 0 auto;
    background-color: var(--card-bg);
    border-radius: var(--border-radius-lg);
    border: 1px solid var(--border-color);
    padding: 30px;
    box-shadow: var(--shadow-md);
}

.photo-upload-zone {
    border: 2px dashed var(--input-border);
    border-radius: var(--border-radius-md);
    padding: 30px;
    text-align: center;
    cursor: pointer;
    transition: border-color var(--transition-fast);
    background-color: rgba(var(--primary-rgb), 0.01);
    margin-bottom: 24px;
}

.photo-upload-zone:hover {
    border-color: var(--primary-color);
}
@media (prefers-color-scheme: dark) {
    .photo-upload-zone:hover {
        border-color: var(--accent-color);
    }
}

.upload-icon {
    font-size: 32px;
    color: var(--text-secondary);
    margin-bottom: 12px;
}

.photo-preview-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 12px;
    margin-top: 16px;
}

.photo-preview-item {
    aspect-ratio: 1;
    border-radius: var(--border-radius-sm);
    overflow: hidden;
    position: relative;
    border: 1px solid var(--border-color);
}

.photo-preview-item img {
    width: 100%;
    height: 100%;
    object-fit: cover;
}

.isbn-auto-fill-btn {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 12px;
    font-weight: 600;
    color: var(--primary-light);
    margin-top: 6px;
}
@media (prefers-color-scheme: dark) {
    .isbn-auto-fill-btn {
        color: var(--accent-color);
    }
}

/* ==========================================================================
   Mypage View
   ========================================================================== */
.mypage-container {
    display: grid;
    grid-template-columns: 1fr 2.5fr;
    gap: 30px;
}

@media (max-width: 768px) {
    .mypage-container {
        grid-template-columns: 1fr;
    }
}

.mypage-sidebar {
    background-color: var(--card-bg);
    border-radius: var(--border-radius-md);
    border: 1px solid var(--border-color);
    padding: 24px;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 16px;
    height: fit-content;
}

.mypage-avatar {
    width: 80px;
    height: 80px;
    border-radius: 50%;
    background-color: var(--primary-color);
    color: #ffffff;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 32px;
    font-weight: 700;
}
@media (prefers-color-scheme: dark) {
    .mypage-avatar {
        background-color: var(--accent-color);
        color: #0b0f19;
    }
}

.mypage-username {
    font-size: 18px;
    font-weight: 700;
}

.mypage-meta {
    font-size: 12px;
    color: var(--text-secondary);
    text-align: center;
}

.mypage-wallet-box {
    background-color: rgba(var(--primary-rgb), 0.05);
    border-radius: var(--border-radius-md);
    padding: 16px;
    width: 100%;
    text-align: center;
    margin-top: 10px;
}

.mypage-wallet-title {
    font-size: 11px;
    color: var(--text-secondary);
    text-transform: uppercase;
}

.mypage-wallet-val {
    font-family: 'Outfit', sans-serif;
    font-size: 24px;
    font-weight: 800;
    color: var(--primary-color);
}
@media (prefers-color-scheme: dark) {
    .mypage-wallet-val {
        color: #ffffff;
    }
}

/* My Tabs & List */
.mypage-tabs {
    display: flex;
    border-bottom: 1.5px solid var(--border-color);
    margin-bottom: 24px;
}

.tab-btn {
    padding: 12px 24px;
    font-weight: 600;
    font-size: 14px;
    color: var(--text-secondary);
    border-bottom: 3px solid transparent;
    transition: all var(--transition-fast);
}

.tab-btn:hover {
    color: var(--primary-color);
}

.tab-btn.active {
    color: var(--primary-color);
    border-bottom-color: var(--primary-color);
}
@media (prefers-color-scheme: dark) {
    .tab-btn.active {
        color: var(--accent-color);
        border-bottom-color: var(--accent-color);
    }
}

.my-items-list {
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.my-item-row {
    display: flex;
    justify-content: space-between;
    align-items: center;
    background-color: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-md);
    padding: 16px;
    box-shadow: var(--shadow-sm);
    transition: transform var(--transition-fast);
}

.my-item-row:hover {
    transform: translateX(4px);
}

.my-item-left {
    display: flex;
    gap: 16px;
    align-items: center;
}

.my-item-img {
    width: 48px;
    height: 64px;
    object-fit: cover;
    border-radius: var(--border-radius-sm);
}

.my-item-details h4 {
    font-size: 14px;
    font-weight: 700;
    margin-bottom: 4px;
}

.my-item-details p {
    font-size: 11px;
    color: var(--text-secondary);
}

.my-item-right {
    display: flex;
    align-items: center;
    gap: 16px;
}

.my-item-price {
    font-family: 'Outfit', sans-serif;
    font-size: 16px;
    font-weight: 700;
}

/* ==========================================================================
   Toast Notification & Confetti UI
   ========================================================================== */
#toast {
    position: fixed;
    bottom: 30px;
    right: 30px;
    background-color: #333333;
    color: #ffffff;
    padding: 12px 24px;
    border-radius: var(--border-radius-md);
    display: flex;
    align-items: center;
    gap: 12px;
    box-shadow: var(--shadow-lg);
    z-index: 1000;
    transition: transform var(--transition-normal), opacity var(--transition-normal);
}

#toast.toast-hidden {
    opacity: 0;
    transform: translateY(20px);
    pointer-events: none;
}

.toast-icon {
    color: var(--accent-color);
}

/* Confetti CSS */
.confetti-container-hidden {
    display: none;
}

.confetti-container-visible {
    position: fixed;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    pointer-events: none;
    z-index: 999;
    overflow: hidden;
}

.confetti-particle {
    position: absolute;
    top: -20px;
    width: 10px;
    height: 10px;
    background-color: var(--accent-color);
    border-radius: 2px;
    opacity: 0.8;
    animation: confetti-fall 3s linear forwards;
}

@keyframes confetti-fall {
    0% {
        transform: translateY(0) rotate(0deg);
        opacity: 1;
    }
    100% {
        transform: translateY(105vh) rotate(360deg);
        opacity: 0;
    }
}

/* ==========================================================================
   Utilities / Animations / Loaders
   ========================================================================== */
.loading-spinner {
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 100px 0;
}

.spinner {
    width: 40px;
    height: 40px;
    border: 4px solid var(--border-color);
    border-top: 4px solid var(--primary-color);
    border-radius: 50%;
    animation: spin 1s linear infinite;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* Responsive Overrides */
@media (max-width: 768px) {
    .app-header {
        height: 60px;
    }
    .header-container {
        padding: 0 16px;
    }
    .header-search-container {
        display: none; /* Mobile search bar is below header */
    }
    .mobile-search-wrapper {
        display: block;
    }
    .nav-menu {
        display: none; /* Bottom Nav used on mobile */
    }
    .app-main {
        padding: 16px 12px calc(var(--mobile-nav-height) + 20px);
    }
    .mobile-bottom-nav {
        display: flex;
    }
    .hero-section {
        padding: 30px 20px;
        margin-bottom: 24px;
    }
    .hero-title {
        font-size: 24px;
    }
    .hero-subtitle {
        font-size: 14px;
        margin-bottom: 16px;
    }
    .hero-stats {
        gap: 20px;
    }
    .details-wrapper {
        grid-template-columns: 1fr;
        gap: 20px;
        padding: 16px;
    }
    .footer-container {
        grid-template-columns: 1fr;
        gap: 24px;
    }
    .footer-disclaimer {
        grid-column: 1;
    }
    .app-footer {
        padding: 30px 16px calc(var(--mobile-nav-height) + 20px);
    }
    #toast {
        left: 20px;
        right: 20px;
        bottom: 80px;
    }
}