/* ==================== CSS Variables ==================== */
:root {
    /* Colors - Digital Library Theme */
    --bg-primary: #0f172a;
    --bg-secondary: #1e293b;
    --bg-tertiary: #334155;
    --bg-card: rgba(30, 41, 59, 0.8);
    --bg-hover: rgba(14, 165, 233, 0.1);
    
    --accent-primary: #0ea5e9;
    --accent-secondary: #8b5cf6;
    --accent-tertiary: #10b981;
    --accent-warning: #f59e0b;
    
    --text-primary: #f1f5f9;
    --text-secondary: #94a3b8;
    --text-muted: #64748b;
    
    --border-color: rgba(255, 255, 255, 0.1);
    --border-active: var(--accent-primary);
    
    /* Gradients */
    --gradient-primary: linear-gradient(135deg, var(--accent-primary), var(--accent-secondary));
    --gradient-glow: 0 0 20px rgba(14, 165, 233, 0.3);
    
    /* Shadows */
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.5);
    
    /* Spacing */
    --space-xs: 4px;
    --space-sm: 8px;
    --space-md: 16px;
    --space-lg: 24px;
    --space-xl: 32px;
    
    /* Border Radius */
    --radius-sm: 6px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-xl: 16px;
    
    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-normal: 300ms ease;
}

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

html {
    font-size: 16px;
    -webkit-font-smoothing: antialiased;
}

body {
    font-family: 'Source Sans 3', -apple-system, BlinkMacSystemFont, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    min-height: 100dvh;
    line-height: 1.6;
}

/* ==================== App Container ==================== */
.app-container {
    max-width: 1400px;
    margin: 0 auto;
    padding: var(--space-lg);
    min-height: 100dvh;
    display: flex;
    flex-direction: column;
}

/* ==================== Header ==================== */
.header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-bottom: var(--space-lg);
    border-bottom: 1px solid var(--border-color);
    margin-bottom: var(--space-xl);
}

.header-brand {
    display: flex;
    align-items: center;
    gap: var(--space-md);
}

.logo {
    width: 48px;
    height: 48px;
    background: var(--gradient-primary);
    border-radius: var(--radius-lg);
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: var(--gradient-glow);
}

.logo svg {
    width: 26px;
    height: 26px;
    color: white;
}

.brand-text h1 {
    font-size: 1.375rem;
    font-weight: 700;
    color: var(--text-primary);
    letter-spacing: -0.02em;
}

.brand-text span {
    font-size: 0.8125rem;
    color: var(--text-secondary);
}

.header-stats {
    display: flex;
    gap: var(--space-xl);
}

.stat-item {
    text-align: center;
}

.stat-value {
    display: block;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--accent-primary);
}

.stat-label {
    font-size: 0.75rem;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.btn-settings {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    padding: var(--space-sm) var(--space-md);
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    color: var(--text-secondary);
    font-family: inherit;
    font-size: 0.875rem;
    cursor: pointer;
    transition: var(--transition-fast);
}

.btn-settings svg {
    width: 18px;
    height: 18px;
}

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

/* ==================== Main Content ==================== */
.main-content {
    display: grid;
    grid-template-columns: 320px 1fr;
    gap: var(--space-xl);
    flex: 1;
    min-height: 0;
}

/* ==================== Knowledge Base Panel ==================== */
.kb-panel {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-xl);
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

.panel-section {
    padding: var(--space-lg);
}

.panel-section:first-child {
    border-bottom: 1px solid var(--border-color);
}

.documents-section {
    flex: 1;
    display: flex;
    flex-direction: column;
    min-height: 0;
}

.section-title {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-secondary);
    margin-bottom: var(--space-md);
    display: flex;
    justify-content: space-between;
    align-items: center;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* Upload Zone */
.upload-zone {
    border: 2px dashed var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    text-align: center;
    cursor: pointer;
    transition: var(--transition-normal);
}

.upload-zone:hover,
.upload-zone.dragover {
    border-color: var(--accent-primary);
    background: var(--bg-hover);
}

.upload-zone svg {
    width: 40px;
    height: 40px;
    color: var(--accent-primary);
    margin-bottom: var(--space-sm);
}

.upload-zone p {
    font-size: 0.9375rem;
    color: var(--text-primary);
    margin-bottom: var(--space-xs);
}

.upload-zone span {
    font-size: 0.8125rem;
    color: var(--text-muted);
}

.upload-types {
    margin-top: var(--space-sm);
    font-size: 0.75rem;
    color: var(--text-muted);
}

.upload-progress {
    margin-top: var(--space-md);
    display: none;
}

.upload-progress.active {
    display: block;
}

.progress-bar {
    height: 4px;
    background: var(--bg-tertiary);
    border-radius: var(--radius-full);
    overflow: hidden;
    margin-bottom: var(--space-xs);
}

.progress-fill {
    height: 100%;
    background: var(--gradient-primary);
    width: 0%;
    transition: width 0.3s ease;
}

.progress-text {
    font-size: 0.75rem;
    color: var(--text-muted);
}

/* Documents List */
.documents-list {
    flex: 1;
    overflow-y: auto;
    margin: 0 calc(-1 * var(--space-lg));
    padding: 0 var(--space-lg);
}

.documents-list::-webkit-scrollbar {
    width: 4px;
}

.documents-list::-webkit-scrollbar-thumb {
    background: var(--border-color);
    border-radius: var(--radius-full);
}

.empty-state {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: var(--space-xl);
    color: var(--text-muted);
    text-align: center;
}

.empty-state svg {
    width: 48px;
    height: 48px;
    margin-bottom: var(--space-md);
    opacity: 0.5;
}

.empty-state p {
    font-size: 0.9375rem;
    margin-bottom: var(--space-xs);
}

.empty-state span {
    font-size: 0.8125rem;
}

.document-card {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    padding: var(--space-sm);
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    margin-bottom: var(--space-sm);
    transition: var(--transition-fast);
}

.document-card:hover {
    border-color: var(--accent-primary);
}

.doc-icon {
    width: 36px;
    height: 36px;
    background: var(--bg-tertiary);
    border-radius: var(--radius-sm);
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
}

.doc-icon svg {
    width: 18px;
    height: 18px;
    color: var(--accent-primary);
}

.doc-info {
    flex: 1;
    min-width: 0;
}

.doc-name {
    font-size: 0.875rem;
    color: var(--text-primary);
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.doc-meta {
    font-size: 0.75rem;
    color: var(--text-muted);
}

.doc-delete {
    width: 28px;
    height: 28px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: transparent;
    border: none;
    color: var(--text-muted);
    cursor: pointer;
    border-radius: var(--radius-sm);
    transition: var(--transition-fast);
    flex-shrink: 0;
}

.doc-delete:hover {
    background: rgba(239, 68, 68, 0.1);
    color: #ef4444;
}

.doc-delete svg {
    width: 16px;
    height: 16px;
}

.btn-clear-docs {
    width: 28px;
    height: 28px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: transparent;
    border: none;
    color: var(--text-muted);
    cursor: pointer;
    border-radius: var(--radius-sm);
    transition: var(--transition-fast);
}

.btn-clear-docs:hover {
    background: rgba(239, 68, 68, 0.1);
    color: #ef4444;
}

.btn-clear-docs svg {
    width: 16px;
    height: 16px;
}

/* ==================== Q&A Panel ==================== */
.qa-panel {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-xl);
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

.qa-header {
    padding: var(--space-lg);
    border-bottom: 1px solid var(--border-color);
    background: var(--bg-secondary);
}

.qa-header h2 {
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--space-xs);
}

.qa-header p {
    font-size: 0.8125rem;
    color: var(--text-secondary);
}

/* Messages */
.qa-messages {
    flex: 1;
    overflow-y: auto;
    padding: var(--space-lg);
}

.qa-messages::-webkit-scrollbar {
    width: 6px;
}

.qa-messages::-webkit-scrollbar-thumb {
    background: var(--border-color);
    border-radius: var(--radius-full);
}

.welcome-message {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    text-align: center;
    padding: var(--space-2xl);
    min-height: 300px;
}

.welcome-icon {
    width: 64px;
    height: 64px;
    background: var(--gradient-primary);
    border-radius: var(--radius-xl);
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: var(--space-lg);
    box-shadow: var(--gradient-glow);
}

.welcome-icon svg {
    width: 32px;
    height: 32px;
    color: white;
}

.welcome-message h3 {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--space-sm);
}

.welcome-message p {
    font-size: 0.9375rem;
    color: var(--text-secondary);
    max-width: 400px;
    margin-bottom: var(--space-lg);
}

.example-questions {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-sm);
    justify-content: center;
    align-items: center;
}

.example-questions span {
    font-size: 0.8125rem;
    color: var(--text-muted);
}

.example-q {
    padding: var(--space-xs) var(--space-md);
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-full);
    color: var(--text-secondary);
    font-size: 0.8125rem;
    cursor: pointer;
    transition: var(--transition-fast);
}

.example-q:hover {
    background: var(--bg-hover);
    border-color: var(--accent-primary);
    color: var(--accent-primary);
}

/* Message Bubbles */
.message {
    margin-bottom: var(--space-lg);
    animation: fadeIn 0.3s ease;
}

.message.user {
    display: flex;
    justify-content: flex-end;
}

.message.assistant {
    display: flex;
    justify-content: flex-start;
}

.message-bubble {
    max-width: 80%;
    padding: var(--space-md);
    border-radius: var(--radius-lg);
    line-height: 1.7;
}

.message.user .message-bubble {
    background: var(--gradient-primary);
    color: white;
    border-bottom-right-radius: var(--space-xs);
}

.message.assistant .message-bubble {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-bottom-left-radius: var(--space-xs);
}

.message-content {
    font-size: 0.9375rem;
}

.message-content p {
    margin-bottom: var(--space-sm);
}

.message-content p:last-child {
    margin-bottom: 0;
}

.message-time {
    font-size: 0.75rem;
    color: var(--text-muted);
    margin-top: var(--space-xs);
}

.message.user .message-time {
    color: rgba(255, 255, 255, 0.7);
}

/* Source Citations */
.sources {
    margin-top: var(--space-md);
    padding-top: var(--space-md);
    border-top: 1px solid var(--border-color);
}

.sources-title {
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-bottom: var(--space-sm);
}

.source-item {
    font-size: 0.8125rem;
    color: var(--text-secondary);
    padding: var(--space-sm);
    background: var(--bg-tertiary);
    border-radius: var(--radius-sm);
    margin-bottom: var(--space-xs);
}

.source-item:last-child {
    margin-bottom: 0;
}

/* Loading */
.loading-indicator {
    display: flex;
    gap: var(--space-sm);
    padding: var(--space-md);
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    border-bottom-left-radius: var(--space-xs);
    width: fit-content;
}

.loading-dot {
    width: 8px;
    height: 8px;
    background: var(--accent-primary);
    border-radius: 50%;
    animation: bounce 1.4s ease-in-out infinite;
}

.loading-dot:nth-child(1) { animation-delay: 0s; }
.loading-dot:nth-child(2) { animation-delay: 0.2s; }
.loading-dot:nth-child(3) { animation-delay: 0.4s; }

/* Input Area */
.qa-input-area {
    padding: var(--space-lg);
    border-top: 1px solid var(--border-color);
    background: var(--bg-secondary);
}

.qa-input-wrapper {
    display: flex;
    gap: var(--space-sm);
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: var(--space-sm);
    transition: var(--transition-fast);
}

.qa-input-wrapper:focus-within {
    border-color: var(--accent-primary);
}

.qa-input-wrapper textarea {
    flex: 1;
    background: transparent;
    border: none;
    color: var(--text-primary);
    font-family: inherit;
    font-size: 0.9375rem;
    line-height: 1.5;
    resize: none;
    outline: none;
    max-height: 120px;
    padding: var(--space-sm);
}

.qa-input-wrapper textarea::placeholder {
    color: var(--text-muted);
}

.send-btn {
    width: 44px;
    height: 44px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--gradient-primary);
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: var(--transition-fast);
    flex-shrink: 0;
}

.send-btn svg {
    width: 20px;
    height: 20px;
    color: white;
}

.send-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

.send-btn:not(:disabled):hover {
    transform: scale(1.05);
}

.send-btn .icon-loading {
    display: none;
    animation: spin 1s linear infinite;
}

.send-btn.loading .icon-send {
    display: none;
}

.send-btn.loading .icon-loading {
    display: block;
}

.input-hint {
    font-size: 0.75rem;
    color: var(--text-muted);
    text-align: center;
    margin-top: var(--space-sm);
}

/* ==================== Modal ==================== */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.7);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
    opacity: 0;
    visibility: hidden;
    transition: var(--transition-normal);
}

.modal-overlay.active {
    opacity: 1;
    visibility: visible;
}

.modal {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-xl);
    width: 90%;
    max-width: 420px;
    overflow: hidden;
    transform: scale(0.95);
    transition: var(--transition-normal);
}

.modal-overlay.active .modal {
    transform: scale(1);
}

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

.modal-header h2 {
    font-size: 1.125rem;
    font-weight: 600;
}

.close-btn {
    width: 32px;
    height: 32px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: transparent;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    border-radius: var(--radius-sm);
    transition: var(--transition-fast);
}

.close-btn svg {
    width: 20px;
    height: 20px;
}

.close-btn:hover {
    background: var(--bg-hover);
    color: var(--text-primary);
}

.modal-body {
    padding: var(--space-lg);
}

.setting-group {
    margin-bottom: var(--space-lg);
}

.setting-group:last-child {
    margin-bottom: 0;
}

.setting-group label {
    display: block;
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--text-secondary);
    margin-bottom: var(--space-sm);
}

.setting-group input,
.setting-group select {
    width: 100%;
    padding: var(--space-sm) var(--space-md);
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    font-family: inherit;
    font-size: 0.9375rem;
    color: var(--text-primary);
    outline: none;
    transition: var(--transition-fast);
}

.setting-group input:focus,
.setting-group select:focus {
    border-color: var(--accent-primary);
}

.modal-footer {
    padding: var(--space-lg);
    border-top: 1px solid var(--border-color);
    display: flex;
    justify-content: flex-end;
}

.btn-primary {
    padding: var(--space-sm) var(--space-xl);
    background: var(--accent-primary);
    border: none;
    border-radius: var(--radius-md);
    color: white;
    font-family: inherit;
    font-size: 0.9375rem;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition-fast);
}

.btn-primary:hover {
    opacity: 0.9;
}

/* ==================== Toast ==================== */
.toast {
    position: fixed;
    bottom: 30px;
    left: 50%;
    transform: translateX(-50%);
    background: var(--text-primary);
    color: var(--bg-primary);
    padding: var(--space-sm) var(--space-xl);
    border-radius: var(--radius-md);
    font-size: 0.875rem;
    z-index: 1001;
    animation: slideUp 0.3s ease;
}

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

@keyframes bounce {
    0%, 80%, 100% { transform: scale(0); }
    40% { transform: scale(1); }
}

@keyframes spin {
    from { transform: rotate(0deg); }
    to { transform: rotate(360deg); }
}

@keyframes slideUp {
    from {
        opacity: 0;
        transform: translate(-50%, 20px);
    }
    to {
        opacity: 1;
        transform: translate(-50%, 0);
    }
}

/* ==================== Responsive ==================== */
@media (max-width: 900px) {
    .main-content {
        grid-template-columns: 1fr;
    }
    
    .kb-panel {
        max-height: 300px;
    }
}

@media (max-width: 600px) {
    .app-container {
        padding: var(--space-md);
    }
    
    .header {
        flex-direction: column;
        gap: var(--space-md);
        text-align: center;
    }
    
    .header-brand {
        flex-direction: column;
    }
    
    .welcome-message {
        padding: var(--space-lg);
    }
    
    .message-bubble {
        max-width: 95%;
    }
}

/* ==================== Accessibility ==================== */
@media (prefers-reduced-motion: reduce) {
    *, *::before, *::after {
        animation-duration: 0.01ms !important;
        transition-duration: 0.01ms !important;
    }
}

:focus-visible {
    outline: 2px solid var(--accent-primary);
    outline-offset: 2px;
}