/* Modern Premium Style Sheet for English Memorization Assistant (v3.0) */

/* Design Tokens & Variable declarations */
:root {
    --accent-rgb: 37, 99, 235; /* Cobalt Blue (37, 99, 235 is #2563eb) */
    --accent: #2563eb; 
    --accent-hover: #1d4ed8; 
    --accent-glow: rgba(var(--accent-rgb), 0.15);
    
    /* Dark Theme Variables (Default) */
    --bg-app: #0f172a; /* Slate 900 */
    --bg-sidebar: #1e293b; /* Slate 800 */
    --bg-card: rgba(30, 41, 59, 0.7); /* Translucent Slate 800 */
    --border-color: rgba(255, 255, 255, 0.08);
    --border-hover: rgba(var(--accent-rgb), 0.4);
    
    --text-primary: #f8fafc; /* Slate 50 */
    --text-secondary: #94a3b8; /* Slate 400 */
    --text-muted: #64748b; /* Slate 500 */
    
    --success: #10b981; /* Emerald 500 */
    --success-bg: rgba(16, 185, 129, 0.12);
    --success-border: rgba(16, 185, 129, 0.2);
    
    --danger: #ef4444; /* Red 500 */
    --danger-bg: rgba(239, 68, 68, 0.12);
    --danger-border: rgba(239, 68, 68, 0.2);
    
    --highlight-zh: rgba(var(--accent-rgb), 0.12);
    --highlight-en: rgba(var(--accent-rgb), 0.12);
    --highlight-border: var(--accent);

    --font-heading: 'Outfit', 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    --font-body: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang SC", "Microsoft YaHei", sans-serif;
    
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --shadow-glow: 0 0 20px 0 rgba(var(--accent-rgb), 0.15);
    
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 20px;
    
    --transition-fast: 0.15s ease;
    --transition-normal: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    --bg-topbar: rgba(15, 23, 42, 0.6);
}

body.light-theme {
    --accent-rgb: 37, 99, 235;
    --accent: #2563eb;
    --accent-hover: #1d4ed8;
    --accent-glow: rgba(var(--accent-rgb), 0.08);

    --bg-app: #f8fafc; /* Slate 50 */
    --bg-sidebar: #ffffff; /* White */
    --bg-card: rgba(255, 255, 255, 0.85);
    --border-color: rgba(15, 23, 42, 0.08); /* Translucent Slate 900 */
    --border-hover: rgba(var(--accent-rgb), 0.4);
    
    --text-primary: #0f172a; /* Slate 900 */
    --text-secondary: #475569; /* Slate 600 */
    --text-muted: #94a3b8; /* Slate 400 */
    
    --success: #10b981;
    --success-bg: rgba(16, 185, 129, 0.08);
    --success-border: rgba(16, 185, 129, 0.15);
    
    --danger: #ef4444;
    --danger-bg: rgba(239, 68, 68, 0.08);
    --danger-border: rgba(239, 68, 68, 0.15);
    
    --highlight-zh: rgba(var(--accent-rgb), 0.08);
    --highlight-en: rgba(var(--accent-rgb), 0.08);
    --highlight-border: var(--accent);
    
    --shadow-sm: 0 1px 2px 0 rgba(15, 23, 42, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(15, 23, 42, 0.05), 0 2px 4px -1px rgba(15, 23, 42, 0.03);
    --shadow-lg: 0 10px 15px -3px rgba(15, 23, 42, 0.05), 0 4px 6px -2px rgba(15, 23, 42, 0.03);
    --shadow-glow: 0 0 20px 0 rgba(var(--accent-rgb), 0.08);
    --bg-topbar: rgba(255, 255, 255, 0.75);
}

/* Reset and Base Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    -webkit-tap-highlight-color: transparent;
}

body {
    background-color: var(--bg-app);
    color: var(--text-primary);
    font-family: var(--font-body);
    font-size: 15px;
    line-height: 1.6;
    overflow-x: hidden;
    height: 100vh;
}

/* Scrollbar Customization */
::-webkit-scrollbar {
    width: 6px;
    height: 6px;
}
::-webkit-scrollbar-track {
    background: transparent;
}
::-webkit-scrollbar-thumb {
    background: rgba(255, 255, 255, 0.1);
    border-radius: 3px;
}
::-webkit-scrollbar-thumb:hover {
    background: rgba(255, 255, 255, 0.25);
}

/* Main Layout Structure */
.app-container {
    display: flex;
    height: 100vh;
    width: 100vw;
    position: relative;
    overflow: hidden;
}

/* Sidebar Styling (Desktop) */
.sidebar {
    width: 320px;
    background-color: var(--bg-sidebar);
    border-right: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    height: 100%;
    z-index: 100;
    transition: transform var(--transition-normal);
}

.sidebar-header {
    padding: 24px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid var(--border-color);
}

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

.logo-icon {
    font-size: 24px;
}

.logo h1 {
    font-family: var(--font-heading);
    font-size: 20px;
    font-weight: 700;
    color: var(--text-primary);
    letter-spacing: -0.5px;
}

.close-sidebar-btn {
    display: none; /* Desktop hidden */
    background: none;
    border: none;
    color: var(--text-secondary);
    font-size: 20px;
    cursor: pointer;
    padding: 4px;
}

/* Stats Card in Sidebar */
.stats-card {
    margin: 20px 24px 10px 24px;
    padding: 20px;
    background: rgba(255, 255, 255, 0.02);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
}

.stats-title {
    font-size: 13px;
    font-weight: 600;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.5px;
    margin-bottom: 12px;
}

.stats-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
    margin-bottom: 16px;
}

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

.stat-value {
    font-family: var(--font-heading);
    font-size: 24px;
    font-weight: 700;
    color: var(--text-primary);
}

.stat-label {
    font-size: 12px;
    color: var(--text-muted);
}

/* Progress bar inside Stats Card */
.progress-container {
    display: flex;
    flex-direction: column;
    gap: 6px;
}

.progress-bar-label {
    display: flex;
    justify-content: space-between;
    font-size: 11px;
    color: var(--text-secondary);
}

.progress-track {
    height: 6px;
    background: rgba(255, 255, 255, 0.05);
    border-radius: 3px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: var(--accent);
    border-radius: 3px;
    transition: width var(--transition-slow);
    box-shadow: 0 0 10px rgba(var(--accent-rgb), 0.5);
}

/* Sidebar Navigation Menu */
.unit-menu {
    flex: 1;
    overflow-y: auto;
    padding: 10px 24px;
}

.menu-label {
    font-size: 11px;
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.8px;
    margin-bottom: 8px;
}

.special-list, .unit-list {
    list-style: none;
    margin-bottom: 16px;
}

.unit-item {
    margin-bottom: 4px;
}

.unit-link {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 10px 14px;
    color: var(--text-secondary);
    text-decoration: none;
    border-radius: var(--radius-sm);
    transition: var(--transition-fast);
    cursor: pointer;
    font-weight: 500;
    font-size: 14px;
}

.unit-link:hover {
    color: var(--text-primary);
    background: rgba(255, 255, 255, 0.03);
}

.unit-item.active .unit-link {
    color: var(--text-primary);
    background: var(--accent-glow);
    border: 1px solid rgba(var(--accent-rgb), 0.2);
    box-shadow: var(--shadow-sm);
}

.unit-badge {
    font-size: 11px;
    padding: 2px 6px;
    border-radius: 10px;
    background: rgba(255, 255, 255, 0.05);
    color: var(--text-muted);
}

.unit-item.active .unit-badge {
    background: var(--accent);
    color: white;
}

.sidebar-footer {
    padding: 20px 24px;
    border-top: 1px solid var(--border-color);
}

.version {
    font-size: 11px;
    color: var(--text-muted);
    text-align: center;
    margin-top: 12px;
}

/* Button UI Components */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    font-family: var(--font-body);
    font-size: 14px;
    font-weight: 600;
    padding: 10px 18px;
    border-radius: var(--radius-sm);
    border: 1px solid transparent;
    cursor: pointer;
    transition: var(--transition-fast);
}

.btn-primary {
    background: var(--accent);
    color: white;
}

.btn-primary:hover {
    background: var(--accent-hover);
    transform: translateY(-1px);
    box-shadow: 0 4px 12px rgba(var(--accent-rgb), 0.3);
}

.btn-secondary {
    background: rgba(255, 255, 255, 0.03);
    color: var(--text-secondary);
    border-color: var(--border-color);
}

.btn-secondary:hover {
    background: rgba(255, 255, 255, 0.08);
    color: var(--text-primary);
    border-color: rgba(255, 255, 255, 0.15);
}

.btn-sm {
    padding: 6px 12px;
    font-size: 12px;
}

.btn-block {
    display: flex;
    width: 100%;
}

.btn-danger {
    background: var(--danger-bg);
    color: var(--danger);
    border-color: var(--danger-border);
}
.btn-danger:hover {
    background: rgba(239, 68, 68, 0.2);
    color: #ff6b6b;
}

.btn-success {
    background: var(--success-bg);
    color: var(--success);
    border-color: var(--success-border);
}
.btn-success:hover {
    background: rgba(16, 185, 129, 0.2);
    color: #34d399;
}

/* Main Content Layout */
.main-content {
    flex: 1;
    display: flex;
    flex-direction: column;
    height: 100%;
    overflow: hidden;
    position: relative;
}

/* Top Nav Bar */
.top-bar {
    height: 64px;
    padding: 0 32px;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    justify-content: space-between;
    background: var(--bg-topbar);
    backdrop-filter: blur(12px);
    z-index: 10;
}

.menu-toggle-btn {
    display: none; /* Desktop hidden */
    background: none;
    border: none;
    color: var(--text-primary);
    cursor: pointer;
    padding: 8px;
    margin-left: -8px;
}

.current-unit-title {
    font-family: var(--font-heading);
    font-size: 18px;
    font-weight: 700;
}

/* Top Bar Card Navigator */
.card-navigator {
    display: flex;
    align-items: center;
    gap: 12px;
    background: rgba(255, 255, 255, 0.02);
    border: 1px solid var(--border-color);
    padding: 4px 8px;
    border-radius: 20px;
}

.nav-arrow-btn {
    background: none;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    width: 28px;
    height: 28px;
    border-radius: 50%;
    transition: var(--transition-fast);
}

.nav-arrow-btn:hover {
    background: rgba(255, 255, 255, 0.06);
    color: var(--text-primary);
}

.card-indicator {
    font-size: 13px;
    font-weight: 600;
    color: var(--text-primary);
    min-width: 36px;
    text-align: center;
}

/* Content Area Wrapper */
.content-wrapper {
    flex: 1;
    overflow-y: auto;
    padding: 32px;
    display: flex;
    flex-direction: column;
    gap: 24px;
}

/* Toolbar Style */
.toolbar-section {
    display: flex;
    flex-direction: row;
    align-items: center;
    justify-content: space-between;
    flex-wrap: wrap;
    gap: 16px;
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 16px 24px;
    box-shadow: var(--shadow-sm);
    backdrop-filter: blur(8px);
}

.toolbar-main-controls {
    display: flex;
    align-items: center;
    gap: 20px;
    flex-wrap: wrap;
}

/* Switch styling */
.switch-container {
    display: flex;
    align-items: center;
    gap: 12px;
    background: rgba(255, 255, 255, 0.03);
    border: 1px solid var(--border-color);
    padding: 6px 14px;
    border-radius: var(--radius-lg);
    transition: var(--transition-fast);
}

.switch-container:hover {
    border-color: rgba(255, 255, 255, 0.15);
    background: rgba(255, 255, 255, 0.05);
}

.switch-label {
    font-size: 14px;
    font-weight: 600;
    color: var(--text-primary);
    user-select: none;
}

.switch {
    position: relative;
    display: inline-block;
    width: 46px;
    height: 24px;
}

.switch input {
    opacity: 0;
    width: 0;
    height: 0;
}

.slider {
    position: absolute;
    cursor: pointer;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: rgba(255, 255, 255, 0.1);
    transition: var(--transition-fast);
    border: 1px solid var(--border-color);
}

.slider:before {
    position: absolute;
    content: "";
    height: 16px;
    width: 16px;
    left: 3px;
    bottom: 3px;
    background-color: var(--text-primary);
    transition: var(--transition-fast);
}

input:checked + .slider {
    background-color: var(--accent);
    border-color: var(--accent);
}

input:checked + .slider:before {
    transform: translateX(22px);
    background-color: #ffffff;
}

/* Rounded sliders */
.slider.round {
    border-radius: 24px;
}

.slider.round:before {
    border-radius: 50%;
}

.help-tip {
    font-size: 13px;
    color: var(--text-secondary);
}

.option-group {
    display: flex;
    align-items: center;
    gap: 10px;
}

/* Leitner controls */
.leitner-controls {
    display: flex;
    align-items: center;
    gap: 10px;
}

.leitner-badge {
    font-size: 11px;
    font-weight: 700;
    padding: 4px 8px;
    border-radius: 12px;
    background: rgba(255, 255, 255, 0.05);
    color: var(--text-secondary);
}

.leitner-badge.mastered {
    background: var(--success-bg);
    color: var(--success);
    border: 1px solid var(--success-border);
}

.leitner-badge.review {
    background: var(--danger-bg);
    color: var(--danger);
    border: 1px solid var(--danger-border);
}

/* Study Core Container */
.study-core {
    flex: 1;
    position: relative;
    display: flex;
    flex-direction: column;
}

.study-view {
    width: 100%;
    display: flex;
    flex-direction: column;
    gap: 20px;
    animation: fadeIn var(--transition-normal);
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(4px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Desktop Split Layout (Side-by-Side) */
.split-layout {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 24px;
    min-height: 250px;
}

.column-panel {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    display: flex;
    flex-direction: column;
    overflow: hidden;
    backdrop-filter: blur(8px);
    box-shadow: var(--shadow-md);
}

.panel-header {
    padding: 16px 24px;
    border-bottom: 1px solid var(--border-color);
    background: rgba(0, 0, 0, 0.1);
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 14px;
    font-weight: 600;
    color: var(--text-secondary);
}

.lang-badge {
    font-size: 11px;
    font-weight: 700;
    padding: 2px 8px;
    border-radius: 4px;
    text-transform: uppercase;
}

.lang-badge.zh {
    background: rgba(var(--accent-rgb), 0.15);
    color: var(--accent);
}

.lang-badge.en {
    background: rgba(244, 63, 94, 0.15);
    color: #f43f5e;
}

.sentences-list {
    padding: 24px;
    display: flex;
    flex-direction: column;
    gap: 16px;
    overflow-y: auto;
}

/* Interactive Sentence Alignments */
.sentence {
    padding: 10px 14px;
    border-radius: var(--radius-sm);
    border: 1px solid transparent;
    transition: var(--transition-fast);
    cursor: pointer;
    user-select: text;
}

.sentence:hover {
    background: rgba(255, 255, 255, 0.02);
}

/* Highlight alignment classes */
.sentence.highlighted {
    background: var(--highlight-zh);
    border-color: var(--highlight-border);
    box-shadow: var(--shadow-glow);
}

/* Active Recall / Masking Styles */
.mask-mode .masked {
    filter: blur(6px);
    opacity: 0.2;
    background: rgba(255, 255, 255, 0.01);
    user-select: none;
    transition: filter var(--transition-normal), opacity var(--transition-normal);
}

/* When masked sentence is hovered or active (revealed) */
.mask-mode .masked:hover,
.mask-mode .masked.revealed {
    filter: blur(0);
    opacity: 1;
    background: rgba(255, 255, 255, 0.03);
    user-select: text;
}

.mask-mode .masked.revealed {
    border-color: var(--border-hover);
    box-shadow: var(--shadow-sm);
}

/* Mobile Interleaved Layout */
.interleaved-layout {
    display: none;
    flex-direction: column;
    gap: 16px;
}

.interleaved-pair {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 16px;
    display: flex;
    flex-direction: column;
    gap: 10px;
    transition: var(--transition-fast);
}

.interleaved-pair.highlighted {
    border-color: var(--highlight-border);
    background: rgba(var(--accent-rgb), 0.02);
    box-shadow: var(--shadow-glow);
}

.interleaved-prompt {
    font-size: 15px;
    font-weight: 500;
    color: var(--text-primary);
    padding-bottom: 8px;
    border-bottom: 1px dashed var(--border-color);
}

.interleaved-translation {
    font-size: 14px;
    font-weight: 400;
    color: var(--text-secondary);
}

/* Floating lookup Translate Trigger Button */
.floating-translate-btn {
    position: absolute;
    z-index: 1000;
    background: var(--accent);
    color: white;
    padding: 6px 12px;
    border-radius: 20px;
    font-size: 12px;
    font-weight: 600;
    cursor: pointer;
    box-shadow: 0 4px 10px rgba(var(--accent-rgb), 0.4);
    border: 1px solid var(--accent-hover);
    pointer-events: auto;
    user-select: none;
    animation: popIn 0.2s ease;
}

@keyframes popIn {
    from { transform: scale(0.8); opacity: 0; }
    to { transform: scale(1); opacity: 1; }
}

/* Floating translation Tooltip */
.translate-tooltip {
    position: absolute;
    z-index: 999;
    background: rgba(15, 23, 42, 0.9);
    backdrop-filter: blur(10px);
    border: 1px solid var(--border-hover);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-lg), 0 0 15px rgba(var(--accent-rgb), 0.2);
    width: 250px;
    display: flex;
    flex-direction: column;
    overflow: hidden;
    animation: popIn 0.25s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

.tooltip-header {
    background: rgba(255, 255, 255, 0.03);
    padding: 10px 14px;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.tooltip-title {
    font-size: 11px;
    font-weight: 700;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.tooltip-close {
    background: none;
    border: none;
    color: var(--text-muted);
    cursor: pointer;
    font-size: 12px;
}

.tooltip-body {
    padding: 14px;
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.tooltip-q {
    font-size: 13px;
    font-weight: 500;
    color: var(--text-muted);
    font-style: italic;
    word-break: break-all;
}

.tooltip-result {
    font-size: 14px;
    font-weight: 600;
    color: var(--text-primary);
    word-break: break-all;
}

.tooltip-footer {
    padding: 8px 14px;
    background: rgba(0, 0, 0, 0.2);
    border-top: 1px solid var(--border-color);
    display: flex;
    justify-content: flex-end;
}

/* Notebook Table & container styling */
.notebook-container {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    overflow: hidden;
    backdrop-filter: blur(8px);
    box-shadow: var(--shadow-md);
}

.notebook-table {
    width: 100%;
    border-collapse: collapse;
    text-align: left;
}

.notebook-table th, .notebook-table td {
    padding: 16px 24px;
    border-bottom: 1px solid var(--border-color);
}

.notebook-table th {
    background: rgba(0, 0, 0, 0.2);
    font-size: 12px;
    font-weight: 700;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.notebook-table td {
    font-size: 14px;
}

.notebook-table tr:hover td {
    background: rgba(255, 255, 255, 0.01);
}

.notebook-table tr:last-child td {
    border-bottom: none;
}

.notebook-word {
    font-weight: 600;
    color: var(--accent);
}

.notebook-trans {
    color: var(--text-primary);
    transition: filter 0.2s ease, opacity 0.2s ease;
}

.notebook-trans.masked-vocab {
    filter: blur(5px);
    opacity: 0.3;
    user-select: none;
    cursor: pointer;
}

.notebook-trans.masked-vocab:hover {
    filter: blur(0);
    opacity: 1;
}

.notebook-date {
    color: var(--text-muted);
    font-size: 13px;
}

.empty-state {
    padding: 48px;
    text-align: center;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 12px;
}

.empty-icon {
    font-size: 48px;
    opacity: 0.3;
}

.empty-state p {
    font-size: 15px;
    font-weight: 600;
    color: var(--text-secondary);
}

.empty-state .empty-tip {
    font-size: 13px;
    color: var(--text-muted);
    max-width: 400px;
    font-weight: 400;
    line-height: 1.6;
}

/* Sidebar divider line */
.menu-divider {
    border: 0;
    height: 1px;
    background: var(--border-color);
    margin: 16px 0;
}

/* Mobile Sidebar Overlay */
.sidebar-overlay {
    position: absolute;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    background: rgba(0, 0, 0, 0.6);
    z-index: 95;
    opacity: 0;
    pointer-events: none;
    transition: opacity var(--transition-normal);
}

.sidebar-overlay.active {
    opacity: 1;
    pointer-events: auto;
}

/* Dictionary detailed styles */
.dict-main-explain {
    font-size: 14px;
    font-weight: 600;
    color: var(--text-primary);
    line-height: 1.4;
}

.dict-sub-explains {
    margin-top: 8px;
    font-size: 11px;
    color: var(--text-secondary);
    border-top: 1px solid rgba(255, 255, 255, 0.08);
    padding-top: 6px;
    display: flex;
    flex-direction: column;
    gap: 4px;
}

.dict-sub-item {
    word-break: break-all;
    line-height: 1.3;
}

.dict-sub-item strong {
    color: var(--accent);
}

/* Paragraph Card Container */
.paragraphs-list {
    display: flex;
    flex-direction: column;
    gap: 24px;
}

.paragraph-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    overflow: hidden;
    backdrop-filter: blur(8px);
    box-shadow: var(--shadow-sm);
    display: flex;
    flex-direction: column;
    transition: border-color var(--transition-normal);
}

.paragraph-card:hover {
    border-color: var(--border-hover);
}

.paragraph-card-header {
    padding: 12px 24px;
    background: rgba(255, 255, 255, 0.02);
    border-bottom: 1px solid var(--border-color);
    font-size: 13px;
    font-weight: 600;
    color: var(--text-secondary);
    display: flex;
    align-items: center;
}

.paragraph-badge {
    background: rgba(var(--accent-rgb), 0.15);
    color: var(--accent-light);
    padding: 4px 10px;
    border-radius: 4px;
    font-family: var(--font-display);
    font-size: 12px;
}

/* Adjust split layout margin when in paragraph card */
.paragraph-card .split-layout {
    border: none;
    box-shadow: none;
    background: none;
    backdrop-filter: none;
    min-height: auto;
}

.paragraph-card .column-panel {
    border: none;
    border-radius: 0;
    background: none;
    backdrop-filter: none;
    box-shadow: none;
}

.paragraph-card .column-panel:first-child {
    border-right: 1px solid var(--border-color);
}

.paragraph-card .interleaved-layout {
    padding: 16px;
}



/* RESPONSIVE MEDIA QUERIES (MOBILE ADAPTATION) */
@media (max-width: 767px) {
    /* Layout Adjustment */
    .app-container {
        flex-direction: column;
    }

    /* Sidebar Drawer Slide-in Effect */
    .sidebar {
        position: absolute;
        top: 0;
        left: 0;
        height: 100vh;
        width: 280px;
        transform: translateX(-100%);
        box-shadow: none;
        transition: transform var(--transition-normal), box-shadow var(--transition-normal);
    }

    .sidebar.active {
        transform: translateX(0);
        box-shadow: 10px 0 30px rgba(0, 0, 0, 0.35);
    }

    .close-sidebar-btn {
        display: block; /* Show close button on mobile drawer */
    }

    /* Top Bar Mobile Config */
    .top-bar {
        padding: 0 16px;
        height: 56px;
    }

    .menu-toggle-btn {
        display: block; /* Show hamburger button */
    }

    .current-unit-title {
        font-size: 16px;
    }

    /* Content Layout Mobile Config */
    .content-wrapper {
        padding: 16px;
        gap: 16px;
    }

    /* Toolbar Panel Adjust */
    .toolbar-section {
        flex-direction: column;
        align-items: stretch;
        padding: 16px;
        gap: 16px;
    }
    
    .toolbar-main-controls {
        flex-direction: column;
        align-items: flex-start;
        gap: 12px;
        width: 100%;
    }
    
    .switch-container {
        width: 100%;
        justify-content: space-between;
    }
    
    .leitner-controls {
        margin-left: 0;
        width: 100%;
        justify-content: space-between;
        border-top: 1px solid var(--border-color);
        padding-top: 12px;
    }

    /* Notebook table responsive hide columns */
    .notebook-table th:nth-child(3),
    .notebook-table td:nth-child(3) {
        display: none; /* Hide date on mobile */
    }

    .notebook-table th, .notebook-table td {
        padding: 12px 14px;
    }

    .notebook-actions {
        display: flex;
        flex-direction: column;
        gap: 8px;
        width: 100%;
    }
    .notebook-actions button {
        width: 100%;
    }
    
    /* Mobile-optimized Split Layout styling (Top-Bottom Layout) */
    .paragraphs-list.layout-split .split-layout {
        display: flex !important;
        flex-direction: column !important;
        gap: 16px;
    }
    
    .paragraphs-list.layout-split .column-panel {
        width: 100% !important;
        border-right: none !important;
    }
    
    .paragraphs-list.layout-split .column-panel:first-child {
        border-bottom: 1px solid var(--border-color);
        padding-bottom: 16px;
    }
    
    .paragraphs-list.layout-split .sentences-list {
        padding: 8px 4px;
        gap: 8px;
    }
    
    .paragraphs-list.layout-split .panel-header {
        padding: 8px;
        font-size: 11px;
    }
    
    .paragraphs-list.layout-split .lang-badge {
        padding: 1px 4px;
        font-size: 10px;
    }
    
    .paragraphs-list.layout-split .sentence-wrapper {
        gap: 4px;
    }
    
    .paragraphs-list.layout-split .sentence {
        padding: 6px 8px;
        font-size: 13px;
        line-height: 1.4;
        border-radius: 4px;
    }
    
    .paragraphs-list.layout-split .sentence-check-btn {
        padding: 4px 2px;
    }
    
    .paragraphs-list.layout-split .sentence-check-btn svg {
        width: 15px;
        height: 15px;
    }
    
    .toolbar-section {
        flex-direction: column;
        align-items: stretch;
        padding: 16px;
        gap: 12px;
    }
    
    .toolbar-row {
        flex-direction: column;
        align-items: stretch;
        gap: 12px;
    }
    
    .controls-group {
        flex-direction: column;
        align-items: stretch;
        gap: 10px;
    }
    
    .segmented-control {
        width: 100%;
    }
    
    .segmented-control .segment-btn {
        flex: 1;
        justify-content: center;
    }
    
    .unit-progress-container {
        width: 100%;
        justify-content: space-between;
    }
    
    .sentence-card-body {
        padding: 24px 20px;
        min-height: 180px;
    }
    
    .sentence-prompt-text {
        font-size: 16px;
    }
    
    .sentence-translation-text {
        font-size: 15px;
    }
    
    .sentence-card-navigator {
        width: 100%;
        justify-content: space-between;
    }
    
    .sentence-card-navigator button {
        flex: 1;
    }
}

/* --- v3.5 Sleek Controls & Sentence Mastery Styles --- */

/* Layout toggles for paragraph list */
.paragraphs-list.layout-split .split-layout {
    display: grid;
}
.paragraphs-list.layout-split .interleaved-layout {
    display: none;
}

.paragraphs-list.layout-interleaved .split-layout {
    display: none;
}
.paragraphs-list.layout-interleaved .interleaved-layout {
    display: flex;
}

/* Toolbar controls row */
.toolbar-row {
    display: flex;
    align-items: center;
    justify-content: space-between;
    width: 100%;
    flex-wrap: wrap;
    gap: 16px;
}

.controls-group {
    display: flex;
    align-items: center;
    gap: 16px;
    flex-wrap: wrap;
}

.segmented-control {
    display: inline-flex;
    background: rgba(0, 0, 0, 0.2);
    padding: 3px;
    border-radius: var(--radius-md);
    border: 1px solid var(--border-color);
}

.segment-btn {
    background: none;
    border: none;
    color: var(--text-secondary);
    padding: 6px 14px;
    font-family: var(--font-body);
    font-size: 13px;
    font-weight: 600;
    border-radius: 8px;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 6px;
    transition: var(--transition-fast);
}

.segment-btn:hover {
    color: var(--text-primary);
    background: rgba(255, 255, 255, 0.02);
}

.segment-btn.active {
    color: white;
    background: var(--accent);
    box-shadow: var(--shadow-sm);
}

.unit-progress-container {
    display: flex;
    align-items: center;
    background: rgba(16, 185, 129, 0.08);
    border: 1px solid var(--success-border);
    padding: 6px 14px;
    border-radius: var(--radius-lg);
    font-size: 13px;
    font-weight: 600;
    color: var(--success);
}

.progress-label {
    opacity: 0.85;
}

.progress-value {
    font-family: var(--font-heading);
}

.toolbar-info-row {
    margin-top: 4px;
    border-top: 1px solid rgba(255, 255, 255, 0.04);
    padding-top: 10px;
    width: 100%;
}

/* Sentence Mastery checkbox in Paragraph Mode */
.sentence-wrapper {
    display: flex;
    align-items: flex-start;
    gap: 8px;
    position: relative;
    width: 100%;
    transition: opacity var(--transition-fast);
}

.sentence-wrapper.mastered {
    opacity: 0.55;
}

.sentence-wrapper.mastered .sentence {
    font-style: italic;
}

.sentence-check-btn {
    background: none;
    border: none;
    cursor: pointer;
    padding: 8px 4px;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--text-muted);
    transition: color var(--transition-fast), transform var(--transition-fast);
}

.sentence-check-btn:hover {
    color: var(--success);
    transform: scale(1.15);
}

.sentence-check-btn.checked {
    color: var(--success);
}

.sentence-check-btn svg {
    width: 18px;
    height: 18px;
    fill: none;
    stroke: currentColor;
    stroke-width: 2.5;
    stroke-linecap: round;
    stroke-linejoin: round;
}

.sentence-check-btn.checked svg {
    fill: rgba(16, 185, 129, 0.15);
}

/* Single Sentence Card Layout */
.sentence-card-container {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    width: 100%;
    max-width: 800px;
    margin: 20px auto;
    gap: 20px;
}

.sentence-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    width: 100%;
    backdrop-filter: blur(12px);
    box-shadow: var(--shadow-lg), 0 0 30px rgba(var(--accent-rgb), 0.05);
    display: flex;
    flex-direction: column;
    overflow: hidden;
    transition: transform var(--transition-normal), border-color var(--transition-normal);
}

.sentence-card:hover {
    border-color: var(--border-hover);
    box-shadow: var(--shadow-lg), 0 0 30px rgba(var(--accent-rgb), 0.1);
}

.sentence-card-header {
    padding: 16px 24px;
    border-bottom: 1px solid var(--border-color);
    background: rgba(255, 255, 255, 0.01);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.sentence-card-badge {
    background: var(--accent-glow);
    border: 1px solid rgba(var(--accent-rgb), 0.2);
    color: #a5b4fc;
    padding: 4px 10px;
    border-radius: 6px;
    font-size: 12px;
    font-weight: 700;
    font-family: var(--font-heading);
}

.btn-sentence-mastery {
    background: rgba(255, 255, 255, 0.03);
    border: 1px solid var(--border-color);
    color: var(--text-secondary);
    padding: 6px 14px;
    border-radius: var(--radius-sm);
    font-size: 13px;
    font-weight: 600;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 6px;
    transition: var(--transition-fast);
}

.btn-sentence-mastery:hover {
    background: rgba(16, 185, 129, 0.08);
    border-color: var(--success-border);
    color: var(--success);
}

.btn-sentence-mastery.mastered {
    background: var(--success-bg);
    border-color: var(--success-border);
    color: var(--success);
}

.sentence-card-body {
    padding: 36px 40px;
    display: flex;
    flex-direction: column;
    gap: 24px;
    min-height: 240px;
    justify-content: center;
}

.sentence-prompt-text {
    font-size: 20px;
    font-weight: 600;
    line-height: 1.5;
    color: var(--text-primary);
    text-align: center;
}

.sentence-divider {
    height: 1px;
    background: linear-gradient(90deg, transparent, var(--border-color), transparent);
    margin: 8px 0;
}

.sentence-translation-wrapper {
    display: flex;
    justify-content: center;
    min-height: 60px;
    align-items: center;
}

.sentence-translation-text {
    font-size: 18px;
    font-weight: 500;
    line-height: 1.6;
    color: #38bdf8;
    text-align: center;
    transition: filter var(--transition-normal), opacity var(--transition-normal);
}

.sentence-translation-text.masked {
    filter: blur(8px);
    opacity: 0.15;
    cursor: pointer;
    user-select: none;
}

.sentence-translation-text.masked:hover {
    filter: blur(4px);
    opacity: 0.4;
}

.sentence-translation-text.revealed {
    filter: blur(0);
    opacity: 1;
    user-select: text;
}

.sentence-card-navigator {
    display: flex;
    align-items: center;
    gap: 20px;
    margin-top: 10px;
}

.sentence-navigator-indicator {
    font-family: var(--font-heading);
    font-size: 14px;
    font-weight: 700;
    color: var(--text-secondary);
    min-width: 60px;
    text-align: center;
}

/* --- v4.0 User Account & Supabase Modal Styles --- */

/* Sidebar user card items */
.user-email {
    font-size: 13px;
    font-weight: 600;
    color: var(--text-primary);
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
    max-width: 170px;
}

.sync-status-dot {
    width: 8px;
    height: 8px;
    border-radius: 50%;
    display: inline-block;
    transition: background var(--transition-fast);
}

.sync-status-dot.synced {
    background: var(--success);
    box-shadow: 0 0 8px var(--success);
}

.sync-status-dot.syncing {
    background: #eab308; /* yellow-500 */
    box-shadow: 0 0 8px #eab308;
    animation: pulseSync 1s infinite alternate;
}

.sync-status-dot.error {
    background: var(--danger);
    box-shadow: 0 0 8px var(--danger);
}

.sync-status-dot.offline {
    background: var(--text-muted);
}

@keyframes pulseSync {
    from { opacity: 0.4; }
    to { opacity: 1; }
}

/* Modal Overlay (Background Dim) */
.auth-modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    background: rgba(15, 23, 42, 0.75); /* Slate 900 translucent */
    backdrop-filter: blur(12px);
    z-index: 10000;
    display: flex;
    align-items: center;
    justify-content: center;
    animation: fadeIn var(--transition-fast);
}

/* Modal Content Box */
.auth-modal-content {
    background: rgba(30, 41, 59, 0.85); /* Slate 800 translucent */
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    width: 90%;
    max-width: 420px;
    padding: 32px;
    box-shadow: var(--shadow-lg), 0 0 40px rgba(var(--accent-rgb), 0.1);
    position: relative;
    animation: scaleUp 0.3s cubic-bezier(0.34, 1.56, 0.64, 1);
}

@keyframes scaleUp {
    from { transform: scale(0.9); opacity: 0; }
    to { transform: scale(1); opacity: 1; }
}

.auth-modal-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 24px;
}

.auth-modal-header h3 {
    font-family: var(--font-heading);
    font-size: 20px;
    font-weight: 700;
    color: var(--text-primary);
}

.auth-modal-close {
    background: none;
    border: none;
    color: var(--text-secondary);
    font-size: 20px;
    cursor: pointer;
    transition: var(--transition-fast);
    padding: 4px;
}

.auth-modal-close:hover {
    color: var(--text-primary);
    transform: rotate(90deg);
}

/* Tab selectors inside Modal */
.auth-tabs {
    display: flex;
    background: rgba(0, 0, 0, 0.2);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    padding: 3px;
    margin-bottom: 20px;
}

.auth-tab-btn {
    flex: 1;
    background: none;
    border: none;
    color: var(--text-secondary);
    padding: 8px 12px;
    font-family: var(--font-body);
    font-size: 14px;
    font-weight: 600;
    border-radius: 6px;
    cursor: pointer;
    transition: var(--transition-fast);
    text-align: center;
}

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

.auth-tab-btn.active {
    background: var(--accent);
    color: white;
    box-shadow: var(--shadow-sm);
}

/* Form Styles */
.form-group {
    display: flex;
    flex-direction: column;
    gap: 6px;
    text-align: left;
}

.form-label {
    font-size: 12px;
    font-weight: 600;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.form-input {
    background: rgba(15, 23, 42, 0.5); /* Slate 900 */
    border: 1px solid var(--border-color);
    color: var(--text-primary);
    padding: 12px 16px;
    border-radius: var(--radius-sm);
    font-family: var(--font-body);
    font-size: 14px;
    transition: var(--transition-fast);
    width: 100%;
}

.form-input:focus {
    outline: none;
    border-color: var(--accent);
    box-shadow: 0 0 0 2px var(--accent-glow);
    background: rgba(15, 23, 42, 0.7);
}

/* Error/Success Feedbacks */
.auth-error-msg {
    margin-top: 12px;
    font-size: 13px;
    color: #f87171; /* red-400 */
    background: var(--danger-bg);
    border: 1px solid var(--danger-border);
    padding: 8px 12px;
    border-radius: var(--radius-sm);
}

.auth-success-msg {
    margin-top: 12px;
    font-size: 13px;
    color: #34d399; /* emerald-400 */
    background: var(--success-bg);
    border: 1px solid var(--success-border);
    padding: 8px 12px;
    border-radius: var(--radius-sm);
}


/* Theme Toggle & UI styling additions */
.top-bar-right {
    display: flex;
    align-items: center;
    gap: 12px;
}
.theme-toggle-btn {
    background: rgba(255, 255, 255, 0.05);
    border: 1px solid var(--border-color);
    width: 36px;
    height: 36px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 16px;
    cursor: pointer;
    transition: var(--transition-fast);
    color: var(--text-primary);
}
.theme-toggle-btn:hover {
    background: rgba(255, 255, 255, 0.1);
    border-color: var(--accent);
    transform: scale(1.05);
}
body.light-theme .theme-toggle-btn {
    background: rgba(15, 23, 42, 0.04);
    color: var(--text-primary);
}
body.light-theme .theme-toggle-btn:hover {
    background: rgba(15, 23, 42, 0.08);
}

/* Light Theme tweaks for specific panels */
body.light-theme .stats-card {
    background: rgba(0, 0, 0, 0.02);
}
body.light-theme .unit-link:hover {
    background: rgba(0, 0, 0, 0.02);
}
body.light-theme .progress-track {
    background: rgba(0, 0, 0, 0.05);
}
body.light-theme .progress-fill {
    box-shadow: 0 0 10px rgba(var(--accent-rgb), 0.3);
}
body.light-theme .segment-btn {
    background: rgba(0, 0, 0, 0.02);
    color: var(--text-secondary);
}
body.light-theme .segment-btn:hover {
    color: var(--text-primary);
}
body.light-theme .segment-btn.active {
    background: var(--accent);
    color: white;
}
body.light-theme .sentence-card {
    background: white;
    box-shadow: var(--shadow-md);
}
body.light-theme .auth-modal-content {
    background: white;
    box-shadow: var(--shadow-lg);
}
body.light-theme .translate-tooltip {
    background: white;
    box-shadow: var(--shadow-lg);
}
body.light-theme .form-input {
    background: rgba(0, 0, 0, 0.02);
    border: 1px solid rgba(0, 0, 0, 0.08);
    color: var(--text-primary);
}
body.light-theme .form-input:focus {
    border-color: var(--accent);
    background: white;
}
body.light-theme .tooltip-close, body.light-theme .auth-modal-close {
    color: var(--text-secondary);
}
body.light-theme .tooltip-close:hover, body.light-theme .auth-modal-close:hover {
    color: var(--text-primary);
}
body.light-theme .tooltip-q {
    color: var(--text-primary);
}

.password-input-wrapper {
    position: relative;
    display: flex;
    width: 100%;
}
.password-input-wrapper .form-input {
    padding-right: 40px;
    width: 100%;
}
.toggle-password-btn {
    position: absolute;
    right: 10px;
    top: 50%;
    transform: translateY(-50%);
    background: none;
    border: none;
    color: var(--text-secondary);
    cursor: pointer;
    font-size: 16px;
    padding: 4px;
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 2;
    transition: var(--transition-fast);
}
.toggle-password-btn:hover {
    color: var(--text-primary);
}

/* Hide native browser password reveal button (e.g., Edge) */
input[type="password"]::-ms-reveal,
input[type="password"]::-ms-clear {
    display: none;
}