/* ==========================================================================
   EXtremum Physics - Design System & Styling
   ========================================================================== */

/* Custom CSS Variables & Themes */
:root {
    --font-primary: 'Outfit', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    --font-mono: 'Fira Code', 'JetBrains Mono', Courier, monospace;

    /* Sleek Cyberpunk/Space Color Palette */
    --bg-base: #040814;
    --bg-sidebar: rgba(6, 12, 28, 0.85);
    --bg-card: rgba(13, 25, 48, 0.55);
    --bg-card-hover: rgba(20, 38, 72, 0.7);
    --bg-input: rgba(9, 18, 38, 0.8);
    
    /* Neon Accent Colors */
    --clr-cyan: #00f0ff;
    --clr-purple: #9d4edd;
    --clr-blue: #3a86c8;
    --clr-success: #10b981;
    --clr-danger: #ef4444;
    --clr-warning: #f59e0b;
    
    /* Text Colors */
    --txt-main: #f8fafc;
    --txt-muted: #94a3b8;
    --txt-dark: #0f172a;
    
    /* Borders and Shadows */
    --border-glass: rgba(255, 255, 255, 0.08);
    --border-glass-active: rgba(0, 240, 255, 0.35);
    --shadow-neon: 0 0 20px rgba(0, 240, 255, 0.15);
    --shadow-purple: 0 0 20px rgba(157, 78, 221, 0.15);
    --shadow-card: 0 8px 32px 0 rgba(0, 0, 0, 0.37);
    
    /* Border Radius */
    --radius-sm: 6px;
    --radius-md: 12px;
    --radius-lg: 20px;
    --radius-round: 50px;
    
    /* Transition speeds */
    --transition-fast: 0.2s ease;
    --transition-normal: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

/* Reset and Base Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

body {
    font-family: var(--font-primary);
    background-color: var(--bg-base);
    color: var(--txt-main);
    min-height: 100vh;
    overflow-x: hidden;
    background-image: 
        radial-gradient(at 10% 10%, rgba(13, 27, 65, 0.4) 0px, transparent 50%),
        radial-gradient(at 90% 80%, rgba(58, 20, 95, 0.3) 0px, transparent 50%);
    background-attachment: fixed;
}

/* Custom Scrollbar for modern feel */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-base);
}

::-webkit-scrollbar-thumb {
    background: rgba(255, 255, 255, 0.1);
    border-radius: var(--radius-sm);
}

::-webkit-scrollbar-thumb:hover {
    background: rgba(0, 240, 255, 0.4);
    box-shadow: 0 0 8px var(--clr-cyan);
}

/* Application Layout */
.app-container {
    display: flex;
    min-height: 100vh;
    position: relative;
}

/* ==========================================================================
   Sidebar Styling
   ========================================================================== */
.sidebar {
    width: 280px;
    background: var(--bg-sidebar);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border-right: 1px solid var(--border-glass);
    padding: 2rem 1.5rem;
    display: flex;
    flex-direction: column;
    height: 100vh;
    position: fixed;
    top: 0;
    left: 0;
    z-index: 100;
    transition: transform var(--transition-normal);
}

.sidebar-header {
    margin-bottom: 2.5rem;
}

.brand-logo {
    font-size: 2.2rem;
    font-weight: 800;
    letter-spacing: -1px;
    text-transform: uppercase;
    background: linear-gradient(135deg, #fff 40%, var(--clr-cyan));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    display: flex;
    align-items: center;
    gap: 0.2rem;
    text-shadow: 0 0 10px rgba(0, 240, 255, 0.2);
}

.logo-accent {
    color: var(--clr-cyan);
    -webkit-text-fill-color: initial;
    text-shadow: 0 0 15px var(--clr-cyan);
}

.brand-subtitle {
    font-size: 0.75rem;
    font-weight: 600;
    letter-spacing: 3px;
    color: var(--txt-muted);
    text-transform: uppercase;
    margin-top: 0.25rem;
    padding-left: 3px;
}

.sidebar-menu {
    display: flex;
    flex-direction: column;
    gap: 0.4rem;
    flex-grow: 1;
    overflow-y: auto;
}

.nav-item {
    background: transparent;
    border: 1px solid transparent;
    color: var(--txt-muted);
    padding: 0.85rem 1.2rem;
    border-radius: var(--radius-md);
    cursor: pointer;
    font-size: 0.95rem;
    font-weight: 500;
    font-family: var(--font-primary);
    display: flex;
    align-items: center;
    gap: 1rem;
    text-align: left;
    transition: all var(--transition-fast);
}

.nav-item i {
    font-size: 1.1rem;
    width: 20px;
    text-align: center;
    transition: transform var(--transition-fast);
}

.nav-item:hover {
    color: var(--txt-main);
    background: rgba(255, 255, 255, 0.04);
}

.nav-item:hover i {
    transform: scale(1.1);
}

.nav-item.active {
    color: var(--txt-main);
    background: rgba(0, 240, 255, 0.08);
    border-color: rgba(0, 240, 255, 0.2);
    box-shadow: inset 0 0 12px rgba(0, 240, 255, 0.05);
}

.nav-item.active i {
    color: var(--clr-cyan);
    text-shadow: 0 0 10px rgba(0, 240, 255, 0.5);
}

.menu-divider {
    font-size: 0.7rem;
    text-transform: uppercase;
    font-weight: 700;
    color: rgba(255, 255, 255, 0.3);
    letter-spacing: 1.5px;
    margin: 1.5rem 0 0.5rem 0.5rem;
}

.badge {
    background: var(--clr-purple);
    color: #fff;
    font-size: 0.75rem;
    padding: 0.1rem 0.5rem;
    border-radius: var(--radius-round);
    margin-left: auto;
    font-weight: 700;
    box-shadow: 0 0 10px rgba(157, 78, 221, 0.4);
}

.sidebar-footer {
    padding-top: 1.5rem;
    border-top: 1px solid rgba(255, 255, 255, 0.05);
    color: rgba(255, 255, 255, 0.25);
    font-size: 0.75rem;
    text-align: center;
}

.footer-version {
    font-family: var(--font-mono);
    color: rgba(0, 240, 255, 0.4);
    margin-top: 0.25rem;
}

/* ==========================================================================
   Main Content Layout
   ========================================================================== */
.main-content {
    flex-grow: 1;
    margin-left: 280px;
    padding: 2rem;
    max-width: 1400px;
    width: calc(100% - 280px);
}

/* Header & Search Bar */
.top-bar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 2rem;
    margin-bottom: 2rem;
}

.search-container {
    position: relative;
    flex-grow: 1;
    max-width: 650px;
}

.search-icon {
    position: absolute;
    left: 1.2rem;
    top: 50%;
    transform: translateY(-50%);
    color: var(--txt-muted);
    font-size: 1.1rem;
    pointer-events: none;
    transition: color var(--transition-fast);
}

#formula-search-input {
    width: 100%;
    background: var(--bg-input);
    border: 1px solid var(--border-glass);
    border-radius: var(--radius-md);
    padding: 1rem 1rem 1rem 3.2rem;
    color: var(--txt-main);
    font-family: var(--font-primary);
    font-size: 0.95rem;
    outline: none;
    transition: all var(--transition-normal);
    box-shadow: var(--shadow-card);
}

#formula-search-input:focus {
    border-color: var(--clr-cyan);
    box-shadow: 0 0 15px rgba(0, 240, 255, 0.15), var(--shadow-card);
}

#formula-search-input:focus + .search-icon {
    color: var(--clr-cyan);
}

.clear-search-btn {
    position: absolute;
    right: 1.2rem;
    top: 50%;
    transform: translateY(-50%);
    background: transparent;
    border: none;
    color: var(--txt-muted);
    cursor: pointer;
    font-size: 1.2rem;
    display: none;
}

.clear-search-btn:hover {
    color: var(--clr-cyan);
}

/* Dashboard Statistics Dashboard */
.stats-panel {
    display: flex;
    gap: 1rem;
    flex-shrink: 0;
}

.stat-card {
    background: var(--bg-card);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border: 1px solid var(--border-glass);
    padding: 0.75rem 1.5rem;
    border-radius: var(--radius-md);
    text-align: center;
    min-width: 110px;
    box-shadow: var(--shadow-card);
    transition: transform var(--transition-fast);
}

.stat-card:hover {
    transform: translateY(-2px);
    border-color: var(--clr-cyan);
}

.stat-value {
    font-size: 1.5rem;
    font-weight: 800;
    color: var(--clr-cyan);
    text-shadow: 0 0 10px rgba(0, 240, 255, 0.3);
}

.stat-label {
    font-size: 0.75rem;
    text-transform: uppercase;
    font-weight: 700;
    color: var(--txt-muted);
    margin-top: 0.15rem;
}

/* ==========================================================================
   Hero Banner Design
   ========================================================================== */
.hero-banner {
    background: linear-gradient(135deg, rgba(13, 27, 42, 0.7) 0%, rgba(20, 10, 40, 0.7) 100%);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border: 1px solid var(--border-glass);
    padding: 3rem;
    border-radius: var(--radius-lg);
    margin-bottom: 2.5rem;
    position: relative;
    overflow: hidden;
    box-shadow: var(--shadow-card);
}

.hero-content {
    position: relative;
    z-index: 2;
    max-width: 70%;
}

.hero-banner h1 {
    font-size: 2.5rem;
    font-weight: 800;
    margin-bottom: 0.75rem;
    line-height: 1.15;
    background: linear-gradient(to right, #fff, #b4dfff, var(--clr-cyan));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}

.hero-banner p {
    color: var(--txt-muted);
    font-size: 1.1rem;
    line-height: 1.5;
}

.hero-glowing-blob {
    position: absolute;
    width: 300px;
    height: 300px;
    background: radial-gradient(circle, rgba(0, 240, 255, 0.12) 0%, rgba(157, 78, 221, 0.08) 50%, transparent 80%);
    right: -50px;
    top: -50px;
    z-index: 1;
    filter: blur(20px);
    pointer-events: none;
    animation: floatBlob 10s infinite alternate;
}

@keyframes floatBlob {
    0% { transform: translate(0, 0) scale(1); }
    100% { transform: translate(-30px, 30px) scale(1.2); }
}

/* ==========================================================================
   Content Sections Layout
   ========================================================================== */
.content-section {
    display: none;
    animation: fadeIn 0.4s ease;
}

.content-section.active {
    display: block;
}

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

.section-header {
    display: flex;
    justify-content: space-between;
    align-items: baseline;
    margin-bottom: 1.5rem;
    border-bottom: 1px solid rgba(255, 255, 255, 0.05);
    padding-bottom: 0.75rem;
}

.section-header h2 {
    font-size: 1.75rem;
    font-weight: 700;
}

.section-desc {
    color: var(--txt-muted);
    margin-top: 0.35rem;
    font-size: 0.95rem;
}

.results-count {
    font-size: 0.85rem;
    color: var(--txt-muted);
    font-weight: 600;
}

/* ==========================================================================
   Formulas Grid & Cards System
   ========================================================================== */
.formulas-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(360px, 1fr));
    gap: 1.5rem;
}

/* Formula Glass Card */
.formula-card {
    background: var(--bg-card);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border: 1px solid var(--border-glass);
    border-radius: var(--radius-md);
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
    transition: all var(--transition-normal);
    box-shadow: var(--shadow-card);
    position: relative;
    overflow: hidden;
}

.formula-card:hover {
    transform: translateY(-5px);
    border-color: var(--border-glass-active);
    box-shadow: var(--shadow-neon), var(--shadow-card);
    background: var(--bg-card-hover);
}

.formula-card-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
}

.subcategory-badge {
    background: rgba(255, 255, 255, 0.05);
    border: 1px solid rgba(255, 255, 255, 0.05);
    padding: 0.25rem 0.65rem;
    border-radius: var(--radius-sm);
    font-size: 0.75rem;
    font-weight: 700;
    color: var(--clr-blue);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

/* Section-specific badge styles */
.formula-card[data-cat="mechanics"] .subcategory-badge { color: #38bdf8; background: rgba(56, 189, 248, 0.1); }
.formula-card[data-cat="thermodynamics"] .subcategory-badge { color: #fb7185; background: rgba(251, 113, 133, 0.1); }
.formula-card[data-cat="electricity"] .subcategory-badge { color: #facc15; background: rgba(250, 204, 21, 0.1); }
.formula-card[data-cat="optics_quantum"] .subcategory-badge { color: #c084fc; background: rgba(192, 132, 252, 0.1); }

.bookmark-btn {
    background: transparent;
    border: none;
    color: rgba(255, 255, 255, 0.2);
    cursor: pointer;
    font-size: 1.15rem;
    transition: all var(--transition-fast);
    padding: 0.25rem;
}

.bookmark-btn:hover {
    color: var(--clr-cyan);
    transform: scale(1.15);
}

.bookmark-btn.active {
    color: #fbbf24;
    text-shadow: 0 0 8px rgba(251, 191, 36, 0.5);
}

.formula-card-title {
    font-size: 1.15rem;
    font-weight: 600;
    margin-bottom: 1.25rem;
    line-height: 1.4;
    color: var(--txt-main);
}

/* Mathematical Formula Render Box */
.formula-math-box {
    background: rgba(5, 10, 25, 0.6);
    border-radius: var(--radius-md);
    padding: 1.5rem;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 90px;
    margin-bottom: 1.25rem;
    border: 1px solid rgba(255, 255, 255, 0.02);
    box-shadow: inset 0 2px 8px rgba(0, 0, 0, 0.5);
    overflow-x: auto;
}

/* KaTeX custom colors/tweaks */
.katex-display, .katex {
    color: #fff;
    font-size: 1.3rem !important;
}

/* Card Control Panel */
.card-actions {
    display: flex;
    gap: 0.5rem;
    margin-top: auto;
}

.btn {
    font-family: var(--font-primary);
    padding: 0.65rem 1rem;
    border-radius: var(--radius-md);
    font-size: 0.85rem;
    font-weight: 600;
    cursor: pointer;
    border: 1px solid transparent;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    transition: all var(--transition-fast);
}

.btn-primary {
    background: linear-gradient(135deg, var(--clr-cyan) 0%, var(--clr-blue) 100%);
    color: var(--txt-dark);
}

.btn-primary:hover {
    box-shadow: 0 0 15px rgba(0, 240, 255, 0.4);
    transform: translateY(-1px);
}

.btn-secondary {
    background: rgba(255, 255, 255, 0.05);
    border-color: var(--border-glass);
    color: var(--txt-main);
}

.btn-secondary:hover {
    background: rgba(255, 255, 255, 0.1);
}

.btn-glow {
    position: relative;
}

.btn-glow::after {
    content: '';
    position: absolute;
    top: 0; left: 0; right: 0; bottom: 0;
    border-radius: inherit;
    box-shadow: 0 0 20px rgba(0, 240, 255, 0.4);
    opacity: 0;
    transition: opacity var(--transition-fast);
}

.btn-glow:hover::after {
    opacity: 1;
}

.btn-icon-only {
    width: 36px;
    height: 36px;
    padding: 0;
    border-radius: var(--radius-md);
}

.card-actions .btn {
    flex-grow: 1;
}

.card-actions .btn-icon-only {
    flex-grow: 0;
}

/* Expandable Drawer Panel (Details & Calculator) */
.card-drawer {
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.4s cubic-bezier(0, 1, 0, 1); /* Slide effect */
    border-top: 1px solid transparent;
    margin-top: 0;
}

.card-drawer.open {
    max-height: 2000px; /* Large enough value */
    transition: max-height 0.5s ease-in-out;
    border-top: 1px solid rgba(255, 255, 255, 0.08);
    margin-top: 1.25rem;
    padding-top: 1.25rem;
}

/* Variable Descriptions */
.drawer-section-title {
    font-size: 0.8rem;
    text-transform: uppercase;
    font-weight: 700;
    color: var(--clr-cyan);
    letter-spacing: 1px;
    margin-bottom: 0.75rem;
}

.variables-list {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
    margin-bottom: 1.5rem;
}

.variable-item {
    font-size: 0.85rem;
    display: flex;
    align-items: baseline;
    gap: 0.5rem;
    line-height: 1.4;
}

.variable-symbol {
    font-family: var(--font-mono);
    font-weight: 700;
    color: var(--txt-main);
    background: rgba(255, 255, 255, 0.05);
    padding: 0.05rem 0.35rem;
    border-radius: 4px;
    min-width: 28px;
    text-align: center;
}

.variable-unit {
    color: var(--clr-blue);
    font-weight: 500;
}

.variable-desc {
    color: var(--txt-muted);
}

/* Interactive Calculator Panel inside Card */
.calc-container {
    background: rgba(0, 0, 0, 0.25);
    border-radius: var(--radius-md);
    padding: 1rem;
    border: 1px solid rgba(255, 255, 255, 0.03);
}

.calc-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: 0.75rem;
    margin-bottom: 1rem;
}

.calc-input-wrapper {
    position: relative;
    display: flex;
    align-items: center;
}

.calc-label {
    position: absolute;
    left: 0.75rem;
    font-family: var(--font-mono);
    font-weight: 700;
    font-size: 0.85rem;
    color: var(--txt-muted);
}

.calc-input {
    width: 100%;
    background: rgba(5, 10, 25, 0.8);
    border: 1px solid var(--border-glass);
    border-radius: var(--radius-sm);
    padding: 0.5rem 4rem 0.5rem 2.2rem;
    color: var(--txt-main);
    font-family: var(--font-mono);
    font-size: 0.85rem;
    outline: none;
    transition: all var(--transition-fast);
}

.calc-input:focus {
    border-color: var(--clr-cyan);
}

.calc-input:disabled {
    background: rgba(0, 240, 255, 0.03);
    border-color: rgba(0, 240, 255, 0.25);
    color: var(--clr-cyan);
    font-weight: 700;
}

.calc-unit-badge {
    position: absolute;
    right: 2.2rem;
    font-size: 0.75rem;
    color: var(--txt-muted);
    pointer-events: none;
}

.calc-target-selector {
    position: absolute;
    right: 0.5rem;
    background: transparent;
    border: none;
    color: rgba(255, 255, 255, 0.2);
    cursor: pointer;
    padding: 0.25rem;
    transition: color var(--transition-fast);
}

.calc-target-selector:hover {
    color: var(--clr-cyan);
}

.calc-target-selector.active {
    color: var(--clr-cyan);
}

.calc-btn {
    width: 100%;
    font-size: 0.85rem;
    padding: 0.6rem;
}

.calc-error {
    color: var(--clr-danger);
    font-size: 0.75rem;
    margin-top: 0.5rem;
    text-align: center;
    display: none;
}

/* Placeholder states */
.loading-placeholder {
    grid-column: 1 / -1;
    text-align: center;
    padding: 5rem 0;
    color: var(--txt-muted);
    font-size: 1.1rem;
}

.no-results {
    grid-column: 1 / -1;
    text-align: center;
    padding: 4rem 2rem;
    background: var(--bg-card);
    border-radius: var(--radius-lg);
    border: 1px solid var(--border-glass);
}

.no-results i {
    font-size: 3rem;
    color: rgba(255, 255, 255, 0.1);
    margin-bottom: 1rem;
}

.no-results h3 {
    margin-bottom: 0.5rem;
}

.no-results p {
    color: var(--txt-muted);
}

/* ==========================================================================
   Constants Table Section Styling
   ========================================================================== */
.constants-container {
    background: var(--bg-card);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border: 1px solid var(--border-glass);
    border-radius: var(--radius-lg);
    padding: 2rem;
    box-shadow: var(--shadow-card);
}

.constants-search-box {
    position: relative;
    margin-bottom: 1.5rem;
    max-width: 400px;
}

#constant-search-input {
    width: 100%;
    background: var(--bg-input);
    border: 1px solid var(--border-glass);
    border-radius: var(--radius-md);
    padding: 0.75rem 1rem 0.75rem 2.8rem;
    color: var(--txt-main);
    font-family: var(--font-primary);
    outline: none;
    transition: all var(--transition-fast);
}

#constant-search-input:focus {
    border-color: var(--clr-cyan);
}

#constant-search-input:focus + .search-icon {
    color: var(--clr-cyan);
}

.glass-table-wrapper {
    overflow-x: auto;
    border-radius: var(--radius-md);
    border: 1px solid rgba(255, 255, 255, 0.05);
}

.constants-table {
    width: 100%;
    border-collapse: collapse;
    text-align: left;
    font-size: 0.95rem;
}

.constants-table th, .constants-table td {
    padding: 1rem 1.25rem;
    border-bottom: 1px solid rgba(255, 255, 255, 0.05);
}

.constants-table th {
    background: rgba(255, 255, 255, 0.02);
    font-weight: 700;
    color: var(--clr-cyan);
    text-transform: uppercase;
    font-size: 0.8rem;
    letter-spacing: 1px;
}

.constants-table tbody tr {
    transition: background var(--transition-fast);
}

.constants-table tbody tr:hover {
    background: rgba(255, 255, 255, 0.02);
}

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

.const-symbol {
    font-family: var(--font-mono);
    font-weight: 700;
    color: var(--txt-main);
    background: rgba(255, 255, 255, 0.05);
    padding: 0.1rem 0.5rem;
    border-radius: 4px;
}

.const-value {
    font-family: var(--font-mono);
    font-weight: 500;
}

/* ==========================================================================
   Quiz Section & Game Arena Styling
   ========================================================================== */
.quiz-setup-box {
    padding: 2.5rem;
    border-radius: var(--radius-lg);
}

.quiz-setup-box h3 {
    font-size: 1.5rem;
    margin-bottom: 1.5rem;
    font-weight: 700;
}

.setup-group {
    margin-bottom: 2rem;
}

.setup-group label {
    display: block;
    font-size: 0.95rem;
    font-weight: 700;
    color: var(--txt-muted);
    margin-bottom: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

/* Selection Chips */
.chip-group {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
}

.chip {
    background: rgba(255, 255, 255, 0.04);
    border: 1px solid var(--border-glass);
    color: var(--txt-muted);
    padding: 0.5rem 1rem;
    border-radius: var(--radius-round);
    cursor: pointer;
    font-family: var(--font-primary);
    font-size: 0.85rem;
    font-weight: 600;
    transition: all var(--transition-fast);
}

.chip:hover {
    color: var(--txt-main);
    border-color: rgba(255, 255, 255, 0.2);
}

.chip.active {
    background: rgba(0, 240, 255, 0.08);
    border-color: var(--clr-cyan);
    color: var(--clr-cyan);
    box-shadow: 0 0 12px rgba(0, 240, 255, 0.1);
}

/* Game mode selectors */
.mode-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1rem;
}

.mode-card {
    background: rgba(255, 255, 255, 0.02);
    border: 1px solid var(--border-glass);
    border-radius: var(--radius-md);
    padding: 1.5rem;
    cursor: pointer;
    transition: all var(--transition-normal);
}

.mode-card:hover {
    transform: translateY(-2px);
    border-color: rgba(255, 255, 255, 0.15);
    background: rgba(255, 255, 255, 0.04);
}

.mode-card.active {
    border-color: var(--clr-cyan);
    background: rgba(0, 240, 255, 0.03);
    box-shadow: var(--shadow-neon);
}

.mode-icon {
    font-size: 1.75rem;
    color: var(--clr-cyan);
    margin-bottom: 0.75rem;
    text-shadow: 0 0 10px rgba(0, 240, 255, 0.3);
}

.mode-title {
    font-size: 1.1rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
}

.mode-desc {
    font-size: 0.85rem;
    color: var(--txt-muted);
    line-height: 1.4;
}

/* Active Game Arena Board */
.quiz-arena {
    padding: 2rem;
    border-radius: var(--radius-lg);
}

.arena-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1.5rem;
}

.arena-score {
    display: flex;
    gap: 1.5rem;
    font-size: 0.95rem;
    color: var(--txt-muted);
}

.arena-score strong {
    color: var(--txt-main);
    font-size: 1.1rem;
}

.arena-lives {
    display: flex;
    gap: 0.35rem;
}

.arena-lives i {
    font-size: 1.25rem;
    color: rgba(255, 255, 255, 0.1);
    transition: color var(--transition-fast), transform var(--transition-fast);
}

.arena-lives i.active {
    color: var(--clr-danger);
    filter: drop-shadow(0 0 5px rgba(239, 68, 68, 0.5));
}

/* Progress bar */
.arena-progress-bar {
    width: 100%;
    height: 6px;
    background: rgba(255, 255, 255, 0.05);
    border-radius: var(--radius-round);
    overflow: hidden;
    margin-bottom: 2.5rem;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(to right, var(--clr-purple), var(--clr-cyan));
    box-shadow: 0 0 10px var(--clr-cyan);
    transition: width 0.3s ease;
}

/* Question panel container */
.question-container {
    text-align: center;
    margin-bottom: 2.5rem;
}

.question-badge {
    display: inline-block;
    background: rgba(157, 78, 221, 0.1);
    border: 1px solid rgba(157, 78, 221, 0.2);
    color: var(--clr-purple);
    font-size: 0.75rem;
    font-weight: 700;
    padding: 0.25rem 0.75rem;
    border-radius: var(--radius-sm);
    margin-bottom: 1rem;
    text-transform: uppercase;
}

.question-title {
    font-size: 1.4rem;
    font-weight: 700;
    margin-bottom: 1.5rem;
}

.question-formula-box {
    background: rgba(5, 10, 25, 0.5);
    border: 1px solid var(--border-glass);
    border-radius: var(--radius-lg);
    padding: 2rem;
    display: inline-flex;
    justify-content: center;
    align-items: center;
    min-height: 120px;
    min-width: 280px;
    box-shadow: inset 0 4px 12px rgba(0, 0, 0, 0.4);
}

.question-formula-box .katex {
    font-size: 2rem !important;
}

/* Multiple choice layout */
.options-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 1rem;
    margin-bottom: 2rem;
}

.option-btn {
    background: rgba(255, 255, 255, 0.02);
    border: 1px solid var(--border-glass);
    color: var(--txt-main);
    padding: 1.25rem;
    border-radius: var(--radius-md);
    font-family: var(--font-primary);
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-fast);
    text-align: center;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 70px;
}

.option-btn:hover {
    border-color: rgba(255, 255, 255, 0.2);
    background: rgba(255, 255, 255, 0.05);
}

.option-btn:active {
    transform: scale(0.98);
}

/* Question evaluation states */
.option-btn.correct {
    background: rgba(16, 185, 129, 0.15) !important;
    border-color: var(--clr-success) !important;
    color: var(--clr-success) !important;
    box-shadow: 0 0 15px rgba(16, 185, 129, 0.2) !important;
    animation: correctPulse 0.5s ease;
}

.option-btn.wrong {
    background: rgba(239, 68, 68, 0.15) !important;
    border-color: var(--clr-danger) !important;
    color: var(--clr-danger) !important;
    box-shadow: 0 0 15px rgba(239, 68, 68, 0.2) !important;
    animation: wrongShake 0.4s ease;
}

.option-btn:disabled {
    pointer-events: none;
    opacity: 0.6;
}

.option-btn.correct:disabled, .option-btn.wrong:disabled {
    opacity: 1;
}

@keyframes correctPulse {
    0% { transform: scale(1); }
    50% { transform: scale(1.02); }
    100% { transform: scale(1); }
}

@keyframes wrongShake {
    0%, 100% { transform: translateX(0); }
    20%, 60% { transform: translateX(-6px); }
    40%, 80% { transform: translateX(6px); }
}

/* Feedback panel */
.quiz-feedback {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 1.5rem;
    border-top: 1px solid rgba(255, 255, 255, 0.08);
    animation: slideUp 0.3s ease;
}

.feedback-icon {
    width: 48px;
    height: 48px;
    border-radius: var(--radius-round);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.5rem;
    margin-bottom: 0.75rem;
}

.quiz-feedback.correct-feedback .feedback-icon {
    background: rgba(16, 185, 129, 0.15);
    color: var(--clr-success);
    border: 1px solid var(--clr-success);
}

.quiz-feedback.wrong-feedback .feedback-icon {
    background: rgba(239, 68, 68, 0.15);
    color: var(--clr-danger);
    border: 1px solid var(--clr-danger);
}

.feedback-msg {
    font-size: 1.1rem;
    font-weight: 700;
    margin-bottom: 1rem;
}

@keyframes slideUp {
    from { opacity: 0; transform: translateY(15px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Game Over screen details */
.quiz-gameover {
    padding: 3rem;
    text-align: center;
    border-radius: var(--radius-lg);
}

.gameover-icon {
    font-size: 4rem;
    color: #fbbf24;
    margin-bottom: 1.5rem;
    filter: drop-shadow(0 0 15px rgba(251, 191, 36, 0.3));
    animation: trophypulse 2s infinite alternate;
}

@keyframes trophypulse {
    from { transform: scale(1); }
    to { transform: scale(1.08); }
}

.quiz-gameover h3 {
    font-size: 2rem;
    margin-bottom: 0.5rem;
}

.final-score-desc {
    color: var(--txt-muted);
    font-size: 1.1rem;
    margin-bottom: 1.5rem;
}

.final-score-desc span {
    font-weight: 800;
    color: var(--clr-cyan);
}

.feedback-stars {
    display: flex;
    justify-content: center;
    gap: 0.5rem;
    font-size: 2rem;
    color: rgba(255, 255, 255, 0.1);
    margin-bottom: 2.5rem;
}

.feedback-stars i.filled {
    color: #fbbf24;
    text-shadow: 0 0 12px rgba(251, 191, 36, 0.4);
}

.gameover-actions {
    display: flex;
    justify-content: center;
    gap: 1rem;
}

/* Helper Class: Hidden */
.hidden {
    display: none !important;
}

/* Glass Card helper */
.glass-card {
    background: var(--bg-card);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border: 1px solid var(--border-glass);
    box-shadow: var(--shadow-card);
}

/* ==========================================================================
   Mobile responsiveness
   ========================================================================== */
.mobile-sidebar-toggle {
    display: none;
    position: fixed;
    top: 1.25rem;
    left: 1.25rem;
    z-index: 200;
    background: var(--bg-card);
    border: 1px solid var(--border-glass);
    color: var(--txt-main);
    width: 44px;
    height: 44px;
    border-radius: var(--radius-md);
    align-items: center;
    justify-content: center;
    cursor: pointer;
    font-size: 1.25rem;
    box-shadow: var(--shadow-card);
    backdrop-filter: blur(10px);
}

@media (max-width: 1024px) {
    .sidebar {
        transform: translateX(-100%);
    }
    
    .sidebar.open {
        transform: translateX(0);
        box-shadow: 10px 0 30px rgba(0, 0, 0, 0.5);
    }
    
    .main-content {
        margin-left: 0;
        width: 100%;
        padding: 5rem 1.5rem 1.5rem 1.5rem;
    }
    
    .mobile-sidebar-toggle {
        display: flex;
    }
}

@media (max-width: 768px) {
    .top-bar {
        flex-direction: column;
        align-items: stretch;
        gap: 1rem;
    }
    
    .stats-panel {
        justify-content: space-between;
    }
    
    .stat-card {
        flex-grow: 1;
        padding: 0.5rem;
        min-width: unset;
    }
    
    .hero-banner {
        padding: 2rem;
    }
    
    .hero-content {
        max-width: 100%;
    }
    
    .hero-banner h1 {
        font-size: 1.8rem;
    }
    
    .options-grid {
        grid-template-columns: 1fr;
    }
}