@import url('https://rsms.me/inter/inter.css');
    /* Refined Anycert design tokens */
    :root {
      --color-white: #ffffff;
      --color-gray-50: #F5F7FB;
      --color-gray-100: #EEF2F8;
      --color-gray-200: #E2E8F0;
      --color-gray-300: #CBD5E1;
      --color-gray-400: #94A3B8;
      --color-gray-500: #64748B;
      --color-gray-600: #475569;
      --color-gray-700: #334155;
      --color-gray-800: #1E293B;
      --color-gray-900: #0F172A;

      --surface-base: var(--color-gray-50);
      --surface-raised: var(--color-white);
      --surface-muted: #F1F5F9;
      --surface-border: var(--color-gray-200);
      --surface-border-strong: var(--color-gray-300);

      --color-primary: #2563EB;
      --color-primary-hover: #1D4ED8;
      --color-primary-light: #DBEAFE;
      --color-primary-lighter: #EFF6FF;
      --color-primary-dark: #1E3A8A;

      --color-success: #22C55E;
      --color-success-light: #DCFCE7;
      --color-success-bg: #F2FDF5;
      --color-success-text: #166534;
      --color-error: #EF4444;
      --color-error-light: #FEE2E2;
      --color-error-bg: #FEF2F2;
      --color-error-text: #991B1B;
      --color-warning: #F59E0B;
      --color-warning-light: #FEF3C7;
      --color-warning-bg: #FFF7E6;

      --hint-bg: var(--color-primary-lighter);
      --hint-border: color-mix(in srgb, var(--color-primary) 30%, var(--color-white) 70%);
      --hint-border-accent: var(--color-primary);
      --hint-header-text: var(--color-primary-dark);
      --hint-body-text: #1E3A8A;

      --selection-bg: var(--color-primary-light);
      --selection-border: var(--color-primary);

      --font-size-xs: 0.75rem;
      --font-size-sm: 0.8125rem;
      --font-size-base: 0.95rem;
      --font-size-lg: 1rem;
      --font-size-xl: 1.125rem;
      --font-size-2xl: 1.375rem;
      --font-size-3xl: 1.75rem;

      --space-1: 0.5rem;
      --space-2: 0.75rem;
      --space-3: 1rem;
      --space-4: 1.5rem;
      --space-5: 2rem;
      --space-6: 2.5rem;
      --space-8: 3rem;
      --space-10: 4rem;
      --space-12: 5rem;
      --space-16: 6rem;
      --space-20: 7rem;
      --space-24: 8rem;

      --radius-sm: 0.5rem;
      --radius-md: 0.75rem;
      --radius-lg: 1rem;
      --radius-xl: 1.5rem;

      --shadow-subtle: 0 1px 2px rgba(15, 23, 42, 0.08);
      --shadow-soft: 0 6px 16px rgba(15, 23, 42, 0.08);
      --shadow-medium: 0 12px 32px rgba(15, 23, 42, 0.12);
      --shadow-card: 0 18px 40px rgba(15, 23, 42, 0.08);
      --shadow-button-hover: 0 6px 16px rgba(37, 99, 235, 0.24);

      --transition-fast: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
      --transition-medium: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
      --transition-slow: 0.5s cubic-bezier(0.4, 0, 0.2, 1);
      --transition-bounce: 0.22s cubic-bezier(0.33, 1, 0.68, 1);
      --transition-smooth: 0.25s cubic-bezier(0.33, 1, 0.68, 1);

      --surface-translucent: rgba(255, 255, 255, 0.95);
      --surface-translucent-bottom: rgba(255, 255, 255, 0.97);
      --surface-translucent-top: rgba(255, 255, 255, 0.92);
      --overlay: rgba(15, 23, 42, 0.45);
      --focus-ring: rgba(37, 99, 235, 0.28);
      --focus-ring-subtle: rgba(37, 99, 235, 0.16);
      --focus-ring-medium: rgba(37, 99, 235, 0.22);

      --option-hover-bg: color-mix(in srgb, var(--color-primary-light) 60%, var(--color-white) 40%);
      --option-selected-border: var(--color-primary);
      --badge-bg: rgba(37, 99, 235, 0.08);
      --badge-text: #1E3A8A;
      --badge-selected-bg: var(--color-primary);
      --badge-selected-text: var(--color-white);

      --progress-gradient: linear-gradient(90deg, var(--color-primary) 0%, #3B82F6 50%, #60A5FA 100%);
    }

    /* Reset and base styles */
    *, *::before, *::after {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }

    html {
      -webkit-font-smoothing: antialiased;
      -moz-osx-font-smoothing: grayscale;
    }

    body {
      font-family: "Inter", system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
      font-size: var(--font-size-base);
      line-height: 1.5;
      color: var(--color-gray-700);
      background: var(--surface-base);
      background-attachment: fixed;
      position: relative;
      min-height: 100vh;
      font-weight: 400;
      /* Safe area for notched devices */
      padding-left: env(safe-area-inset-left);
      padding-right: env(safe-area-inset-right);
      padding-bottom: env(safe-area-inset-bottom);
    }
    
    body::before {
      content: '';
      position: fixed;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      background-image: 
        radial-gradient(circle at 20% 40%, rgba(37, 99, 235, 0.06) 0%, transparent 60%),
        radial-gradient(circle at 80% 70%, rgba(37, 99, 235, 0.04) 0%, transparent 55%);
      pointer-events: none;
      z-index: 0;
    }
    
    .container, #app, .header {
      position: relative;
      z-index: 1;
    }
    
    /* Global link styling */
    a {
      color: var(--color-primary);
      text-decoration: none;
      transition: color var(--transition-fast);
    }
    
    a:hover {
      color: var(--color-primary-hover);
      text-decoration: underline;
    }
    
    a:focus-visible {
      outline: none;
      box-shadow: 0 0 0 3px var(--focus-ring);
      border-radius: 2px;
    }
    html {
      font-feature-settings: "kern","liga";
      font-kerning: normal;
      text-rendering: optimizeLegibility;
}

    /* Layout primitives */
    .container {
      max-width: 1040px;
      margin: 0 auto;
      padding: 0 var(--space-4);
    }

    @media (max-width: 768px) {
      .container {
        max-width: 100%;
        padding: 0 var(--space-3);
      }
    }

    @media (max-width: 480px) {
      .container {
        padding: 0 var(--space-2);
      }
    }

    /* Header */
    .header {
      position: sticky;
      top: 0;
      z-index: 50;
      background: var(--surface-translucent);
      backdrop-filter: blur(18px);
      -webkit-backdrop-filter: blur(18px);
      border-bottom: 1px solid var(--surface-border);
      box-shadow: 0 1px 0 rgba(15, 23, 42, 0.04);
      height: 60px;
    }

    .header-content {
      display: flex;
      align-items: center;
      justify-content: space-between;
      height: 100%;
      padding: 0 var(--space-3);
    }

    .nav {
      display: flex;
      gap: var(--space-1);
    }

    .nav-link {
      display: flex;
      align-items: center;
      gap: var(--space-2);
      padding: var(--space-2) var(--space-3);
      font-size: var(--font-size-sm);
      font-weight: 500;
      color: var(--color-gray-600);
      text-decoration: none;
      border-radius: var(--radius-md);
      transition: all var(--transition-fast);
      position: relative;
      min-height: 44px;
      border: 1px solid transparent;
    }

    .nav-link:hover {
      color: var(--color-primary-hover);
      background: var(--color-primary-light);
    }

    .nav-link:focus-visible {
      outline: none;
      box-shadow: 0 0 0 3px var(--focus-ring);
    }

    .nav-link.active {
      color: var(--color-primary);
      background: color-mix(in srgb, var(--color-primary-light) 65%, transparent);
      font-weight: 600;
      border: 1px solid var(--color-primary-light);
    }

    .user-menu {
      display: flex;
      align-items: center;
      gap: var(--space-3);
    }

    /* Mobile menu toggle */
    .menu-toggle {
      display: none;
      align-items: center;
      justify-content: center;
      width: 40px;
      height: 40px;
      padding: 0;
      background: transparent;
      border: none;
      color: var(--color-gray-700);
      cursor: pointer;
      border-radius: var(--radius-md);
      transition: background var(--transition-fast);
    }

    .menu-toggle:hover {
      background: rgba(59, 130, 246, 0.08);
      color: var(--color-primary);
    }

    .menu-toggle:focus-visible {
      outline: none;
      box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.28);
    }

    .menu-toggle svg {
      width: 24px;
      height: 24px;
      stroke: currentColor;
      stroke-width: 2;
      stroke-linecap: round;
    }

    /* Mobile nav drawer */
    .nav-drawer {
      position: fixed;
      top: 60px;
      left: 0;
      right: 0;
      bottom: 0;
      background: var(--surface-raised);
      transform: translateX(-100%);
      transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
      z-index: 40;
      overflow-y: auto;
      box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
    }

    .nav-drawer.open {
      transform: translateX(0);
    }

    .nav-drawer .nav {
      flex-direction: column;
      padding: var(--space-4);
      gap: var(--space-2);
    }

    .nav-drawer .nav-link {
      width: 100%;
      justify-content: flex-start;
      padding: var(--space-3) var(--space-4);
      min-height: 48px;
    }

    /* Main content area */
    .main {
      min-height: calc(100vh - 60px);
      padding: var(--space-4) 0 var(--space-10);
    }

    /* Typography */
    .heading-1 {
      font-size: var(--font-size-3xl);
      font-weight: 600;
      letter-spacing: -0.02em;
      line-height: 1.2;
      color: var(--color-gray-900);
      margin-bottom: var(--space-3);
    }

    .heading-2 {
      font-size: var(--font-size-2xl);
      font-weight: 600;
      letter-spacing: -0.015em;
      line-height: 1.3;
      color: var(--color-gray-900);
      margin-bottom: var(--space-3);
    }

    .text-muted {
      color: var(--color-gray-500);
      font-size: var(--font-size-base);
      line-height: 1.6;
      margin-bottom: var(--space-4);
    }

    /* Cards */
    .card {
      background: var(--surface-raised);
      border: 1px solid var(--surface-border);
      border-radius: var(--radius-lg);
      padding: var(--space-4);
      box-shadow: var(--shadow-subtle);
      transition: transform var(--transition-medium), box-shadow var(--transition-medium), border-color var(--transition-medium);
      cursor: pointer;
      position: relative;
      overflow: hidden;
    }

    .card:hover {
      transform: translateY(-2px);
      box-shadow: var(--shadow-soft);
      border-color: var(--surface-border-strong);
      background: var(--surface-raised);
    }
    
    .card:active {
      transform: translateY(-2px);
    }

    .card-title {
      font-size: var(--font-size-lg);
      font-weight: 500;
      color: var(--color-gray-900);
      margin-bottom: var(--space-2);
      line-height: 1.4;
    }

    .card--warroom {
      background: var(--color-error-light);
      border-color: var(--color-error);
      cursor: default;
    }

    .card--warroom .card-title {
      color: var(--color-error);
      margin-bottom: var(--space-3);
    }

    .warroom-status {
      margin-bottom: var(--space-2);
      color: var(--color-gray-700);
      font-weight: 500;
    }

    .warroom-hint {
      margin-bottom: var(--space-4);
      color: var(--color-gray-600);
      font-size: var(--font-size-sm);
    }

    .btn-warroom {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      gap: var(--space-2);
      padding: var(--space-3) var(--space-5);
      border-radius: var(--radius-md);
      border: none;
      background: var(--color-error);
      color: var(--color-white);
      font-weight: 600;
      cursor: pointer;
      transition: transform var(--transition-fast), box-shadow var(--transition-fast);
      width: 100%;
    }

    .btn-warroom:disabled {
      opacity: 0.5;
      cursor: not-allowed;
      transform: none;
      box-shadow: none;
    }

    .btn-warroom:not(:disabled):hover {
      transform: translateY(-1px);
      box-shadow: var(--shadow-soft);
    }

    .btn-warroom:focus-visible {
      outline: none;
      box-shadow: 0 0 0 3px var(--focus-ring);
    }

    .warroom-pill {
      display: inline-flex;
      align-items: center;
      padding: var(--space-1) var(--space-3);
      border-radius: 999px;
      background: var(--color-error-light);
      color: var(--color-error);
      font-size: var(--font-size-sm);
      margin-bottom: var(--space-3);
      font-weight: 600;
    }

    .warroom-feedback {
      margin-top: var(--space-3);
      color: var(--color-error);
      font-weight: 600;
    }

    .card-subtitle {
      font-size: var(--font-size-xs);
      color: var(--color-gray-500);
      text-transform: uppercase;
      letter-spacing: 0.05em;
      font-weight: 500;
      margin-bottom: var(--space-4);
    }

    /* Buttons */
    .btn {
      display: inline-flex;
      align-items: center;
      gap: var(--space-1);
      padding: var(--space-2) var(--space-4);
      font-size: var(--font-size-sm);
      font-weight: 500;
      border-radius: var(--radius-md);
      border: 1px solid transparent;
      cursor: pointer;
      text-decoration: none;
      transition: transform var(--transition-fast), box-shadow var(--transition-fast), background var(--transition-fast), color var(--transition-fast);
      white-space: nowrap;
      min-height: 44px;
      justify-content: center;
    }

    .btn-primary {
      background: var(--color-primary);
      color: var(--color-white);
      border: 1px solid var(--color-primary);
      box-shadow: 0 4px 10px rgba(37, 99, 235, 0.2);
      padding-left: var(--space-5);
      padding-right: var(--space-5);
    }

    .btn-primary:hover {
      background: var(--color-primary-hover);
      border-color: var(--color-primary-hover);
      transform: translateY(-1px);
      box-shadow: var(--shadow-button-hover);
    }

    .btn-primary:active {
      transform: translateY(0);
      box-shadow: 0 2px 6px rgba(15, 23, 42, 0.12);
    }

    .btn-primary:focus-visible {
      outline: none;
      box-shadow: 0 0 0 3px var(--focus-ring), 0 2px 8px rgba(15, 23, 42, 0.1);
    }

    .btn-ghost {
      background: transparent;
      color: var(--color-gray-600);
      border: 1px solid transparent;
    }

    .btn-ghost:hover {
      background: var(--color-primary-light);
      color: var(--color-primary);
      border-color: color-mix(in srgb, var(--color-primary) 20%, transparent);
    }

    .btn-ghost:active {
      background: color-mix(in srgb, var(--color-primary-light) 80%, transparent);
    }

    .btn-quiet {
      background: rgba(15, 23, 42, 0.05);
      color: var(--color-gray-600);
      border: 1px solid transparent;
      font-size: var(--font-size-sm);
      min-height: 40px;
    }

    .btn-quiet:hover {
      background: rgba(37, 99, 235, 0.12);
      color: var(--color-primary);
    }

    .btn-quiet:active {
      background: rgba(37, 99, 235, 0.18);
    }

    .btn-quiet .icon {
      stroke-width: 1.5;
    }

    .btn-ghost:focus-visible {
      outline: none;
      box-shadow: 0 0 0 3px var(--focus-ring);
    }

    .btn-secondary {
      background: var(--surface-raised);
      color: var(--color-gray-600);
      border: 1px solid var(--surface-border);
    }

    .btn-secondary:hover {
      background: var(--surface-muted);
      border-color: var(--surface-border-strong);
      color: var(--color-gray-700);
    }

    .btn-secondary:focus-visible {
      outline: none;
      box-shadow: 0 0 0 3px var(--focus-ring-subtle);
    }

    .btn-sm {
      padding: var(--space-1) var(--space-3);
      font-size: var(--font-size-xs);
      min-height: 36px;
    }

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

    @keyframes thinking-flash {
      0%, 100% { opacity: 0.4; }
      50%      { opacity: 1; }
    }
    .btn-thinking {
      animation: thinking-flash 1s ease-in-out infinite;
      pointer-events: none;       /* prevent double-click */
    }

    /* ==============================
       1) INPUT – neutral when empty; subtle on focus; readable when filled
       ============================== */
    /* Idle (empty) — keep neutral */
    .form-input:placeholder-shown {
      background: var(--surface-raised);
      border-color: var(--surface-border);
    }
    /* Focus — show a ring, not a fill (using token-based focus ring) */
    /* Filled (not focused) — optional gentle tint to signal “has value” */
    .form-input:not(:placeholder-shown):not(:focus) {
      background: color-mix(in srgb, var(--surface-raised) 80%, var(--color-primary-light) 20%);
      border-color: var(--surface-border);
    }
    /* Smooth transitions so state changes feel calm */
    .form-input {
      transition: background .18s ease, border-color .18s ease, box-shadow .18s ease;
    }

    /* AI Explanation styling */
    .ai-explanation {
      background: var(--surface-muted);
      border: 1px solid var(--surface-border);
      border-radius: var(--radius-lg);
      padding: var(--space-4);
      margin-top: var(--space-4);
      line-height: 1.6;
    }

    .feedback-body {
      color: var(--color-gray-800);
      background: transparent;
      padding-top: 0;
      margin-bottom: var(--space-4);
      line-height: 1.6;
      font-size: var(--font-size-base);
    }

    .pill {
      display: inline-flex;
      align-items: center;
      gap: var(--space-2);
      padding: var(--space-1) var(--space-3);
      min-height: 40px;
      font-size: var(--font-size-sm);
      font-weight: 500;
      color: var(--color-gray-600);
      background: var(--surface-raised);
      border-radius: var(--radius-lg);
      border: 1px solid var(--surface-border);
      transition: all var(--transition-fast);
    }

    .pill:hover {
      background: var(--color-primary-light);
      color: var(--color-primary);
      border-color: color-mix(in srgb, var(--color-primary) 40%, var(--surface-border) 60%);
    }

    /* Icons */
    .icon {
      width: 16px;
      height: 16px;
      stroke: currentColor;
      stroke-width: 2;
      stroke-linecap: round;
      stroke-linejoin: round;
      fill: none;
    }

    .icon-sm {
      width: 14px;
      height: 14px;
    }

    /* Quiz specific components */
    .quiz-header {
      display: grid;
      grid-template-columns: 1fr auto;
      align-items: start;
      gap: var(--space-4);
      margin-bottom: var(--space-5);
      padding: 0;
    }
    
    .quiz-header .left {
      display: none;
    }
    
    .quiz-header .center {
      display: flex;
      flex-direction: column;
      align-items: flex-start;
      gap: var(--space-3);
      grid-column: 1;
    }
    
    .quiz-header .right {
      grid-column: 2;
      align-self: start;
    }

    .quiz-title {
      width: 100%;
      display: block;
    }

    /* Clean breadcrumb */
    .breadcrumb {
      display: flex;
      align-items: center;
      gap: 10px;
      flex-wrap: wrap;
    }
    
    /* Quiz header breadcrumb - Tag + Title System (Option 3) */
    .quiz-header .breadcrumb { 
      font-size: 18px;
      font-weight: 500;
      color: var(--color-gray-900);
      letter-spacing: -0.01em;
      line-height: 1.3;
      width: 100%;
    }
    
    /* Certification badge (CISA, Security+, etc) */
    .quiz-header .breadcrumb .crumb.cert {
      display: inline-flex;
      align-items: center;
      padding: 4px 12px;
      background: var(--color-gray-100);
      border-radius: 6px;
      font-size: 13px;
      font-weight: 600;
      color: var(--color-gray-600);
      letter-spacing: 0.01em;
      text-transform: uppercase;
    }
    
    .quiz-header .breadcrumb .crumb.cert a {
      color: inherit;
      text-decoration: none;
    }
    
    .quiz-header .breadcrumb .crumb.cert:hover {
      background: var(--color-gray-200);
    }
    
    /* Domain and subdomain - styled as badges for coherence */
    .quiz-header .breadcrumb .crumb.domain,
    .quiz-header .breadcrumb .crumb.subdomain {
      display: inline-flex;
      align-items: center;
      padding: 4px 12px;
      background: var(--color-gray-100);
      border-radius: 6px;
      font-size: 13px;
      font-weight: 600;
      color: var(--color-gray-600);
      letter-spacing: 0.01em;
      text-transform: uppercase;
    }
    
    .quiz-header .breadcrumb .crumb a,
    .quiz-header .breadcrumb .crumb a:visited,
    .quiz-header .breadcrumb .crumb a:active,
    .quiz-header .breadcrumb .crumb a:focus { 
      color: inherit; 
      text-decoration: none; 
    }
    
    .quiz-header .breadcrumb .crumb.domain:hover,
    .quiz-header .breadcrumb .crumb.subdomain:hover { 
      background: var(--color-gray-200);
    }

    /* Separator - subtle */
    .quiz-header .breadcrumb .sep { 
      color: var(--color-gray-400);
      font-size: 18px;
      font-weight: 300;
    }
    
    @media (max-width: 640px) { 
      .quiz-header .breadcrumb .crumb.cert,
      .quiz-header .breadcrumb .crumb.domain,
      .quiz-header .breadcrumb .crumb.subdomain { 
        font-size: 12px;
        padding: 3px 10px;
      }
      
      .quiz-header .breadcrumb { 
        font-size: 16px;
      }
    }


    /* Micro progress stacked under breadcrumb (quiet) */
    .progress-compact {
      display: flex;
      flex-direction: column;
      align-items: flex-start;
      gap: 6px;
      font-size: var(--font-size-xs);
      color: var(--color-gray-400);
      width: 100%;
    }

    #qcount { 
      font-size: var(--font-size-xs); 
      color: var(--color-gray-500); 
      letter-spacing: .01em;
      font-weight: 500;
    }


    .progress-track {
      width: 100%;
      max-width: 400px;
      height: 6px;
      background: rgba(148, 163, 184, 0.15);
      border-radius: 3px;
      overflow: hidden;
      box-shadow: inset 0 1px 2px rgba(15, 23, 42, 0.04);
    }

    .progress-thumb {
      height: 100%;
      width: 0%;
      background: linear-gradient(90deg, #3B82F6 0%, #60A5FA 100%);
      border-radius: 3px;
      transition: width var(--transition-smooth);
      box-shadow: 0 0 8px rgba(59, 130, 246, 0.3);
    }

    /* Question layout */
    .page--quiz {
      max-width: 900px;
      margin: 1.5rem auto 0;
      padding: 0 var(--space-4);
    }

    .question-card {
      background: var(--color-white);
      border: 1px solid rgba(148, 163, 184, 0.18);
      border-radius: var(--radius-lg);
      padding: clamp(20px, 3vw, 28px);
      margin-bottom: var(--space-5);
      box-shadow: 0 2px 8px rgba(15, 23, 42, 0.04), 0 1px 3px rgba(15, 23, 42, 0.06);
      transition: all var(--transition-fast);
    }
    
    .question-card:hover {
      box-shadow: 0 4px 16px rgba(15, 23, 42, 0.08), 0 2px 8px rgba(15, 23, 42, 0.04);
      transform: translateY(-1px);
    }

    .question-title {
      max-width: none;
      font-size: clamp(1.125rem, 2vw, 1.25rem);
      font-weight: 600;
      line-height: 1.5;
      color: var(--color-gray-900);
      margin-bottom: var(--space-4);
      text-align: left;
    }

    /* Options - Tighter spacing for efficiency */
    .choices {
      display: grid;
      gap: 0.5rem;
      margin-top: 0;
    }

    .option {
      position: relative;
      display: flex;
      align-items: center;
      gap: var(--space-3);
      padding: 14px 16px;
      min-height: 48px;
      background: var(--color-white);
      border: 1px solid var(--color-gray-200);
      border-radius: var(--radius-md);
      cursor: pointer;
      transition: all 0.15s cubic-bezier(0.33, 1, 0.68, 1);
      line-height: 1.5;
      text-align: left;
    }
    
    .option:hover:not(.disabled) {
      background: var(--option-hover-bg);
      border-color: #3B82F6;
      box-shadow: 0 2px 8px rgba(59, 130, 246, 0.12);
    }
    
    .option.selected {
      border-color: #2563EB;
      background: rgba(37, 99, 235, 0.06);
      box-shadow: 0 2px 12px rgba(37, 99, 235, 0.15);
    }


    .option:focus-visible {
      outline: none;
      box-shadow: 0 0 0 3px var(--focus-ring);
    }


    .option.correct {
      background: var(--color-success-bg);
      border-color: var(--color-success-light);
    }

    .option.incorrect {
      background: var(--color-error-bg);
      border-color: var(--color-error-light);
    }

    .option.disabled {
      pointer-events: none;
      opacity: 0.85;
    }

    .option-label {
      display: grid;
      place-items: center;
      width: 28px;
      height: 28px;
      font-weight: 700;
      font-size: 13px;
      border-radius: 50%;
      background: rgba(71, 85, 105, 0.08);
      color: #475569;
      flex-shrink: 0;
      transition: all 0.2s cubic-bezier(0.33, 1, 0.68, 1);
    }
    
    .option.selected .option-label {
      background: linear-gradient(135deg, #2563EB, #3B82F6);
      color: #FFFFFF;
      transform: scale(1.1);
      box-shadow: 0 2px 8px rgba(37, 99, 235, 0.4);
    }
    
    .option.correct .option-label {
      background: #10B981;
      color: var(--color-white);
    }
    
    .option.incorrect .option-label {
      background: #EF4444;
      color: var(--color-white);
    }

    .option-text {
      font-size: var(--font-size-base);
      line-height: 1.5;
      color: var(--color-gray-900);
      font-weight: 400;
      flex: 1;
    }

    .option-check {
      width: 18px;
      height: 18px;
      display: grid;
      place-items: center;
      opacity: 0;
      border: 1px solid var(--color-gray-200);
      border-radius: 50%;
      transition: all var(--transition-fast);
      flex-shrink: 0;
      margin-top: 2px;
    }

    .option.selected .option-check,
    .option.correct .option-check,
    .option.incorrect .option-check {
      opacity: 1;
    }

    .option.selected .option-check {
      background: var(--color-primary);
      border-color: var(--color-primary);
    }

    .option.selected .option-check .icon {
      stroke: var(--color-white);
    }

    .option.correct .option-check {
      background: var(--color-success);
      border-color: var(--color-success);
    }

    .option.correct .option-check .icon {
      stroke: var(--color-white);
    }

    .option.incorrect .option-check {
      background: var(--color-error);
      border-color: var(--color-error);
    }

    .option.incorrect .option-check .icon {
      stroke: var(--color-white);
    }

    /* Feedback - Smooth expansion with reduced jump */
    .feedback-slot {
      max-height: 0;
      opacity: 0;
      overflow: hidden;
      margin-top: 0;
      transition: max-height 0.3s cubic-bezier(0.4, 0, 0.2, 1), 
                  opacity 0.3s cubic-bezier(0.4, 0, 0.2, 1),
                  margin-top 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    }

    .feedback-slot.show {
      max-height: 800px;
      opacity: 1;
      margin-top: var(--space-4);
    }

    .feedback {
      background: var(--color-gray-100);
      border: 1px solid var(--color-gray-200);
      border-radius: var(--radius-lg);
      padding: var(--space-5);
      box-shadow: var(--shadow-subtle);
    }

    .feedback-header {
      display: flex;
      align-items: center;
      gap: var(--space-2);
      margin-bottom: var(--space-4);
      font-weight: 600;
      font-size: var(--font-size-lg);
    }

    .feedback-header.success {
      color: var(--color-success-text);
    }

    .feedback-header.error {
      color: var(--color-error-text);
    }

    .hint-card {
      background: var(--hint-bg);
      border: 1px solid var(--hint-border);
      border-left: 4px solid var(--hint-border-accent);
      border-radius: var(--radius-lg);
      padding: var(--space-5);
      margin-bottom: var(--space-4);
      box-shadow: var(--shadow-subtle);
      overflow: hidden;
      transition: max-height 0.3s cubic-bezier(0.4, 0, 0.2, 1),
                  opacity 0.3s cubic-bezier(0.4, 0, 0.2, 1),
                  margin-bottom 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    }

    .hint-header {
      display: flex;
      align-items: center;
      gap: var(--space-2);
      margin-bottom: var(--space-3);
      font-weight: 500;
      color: var(--hint-header-text);
      font-size: var(--font-size-base);
    }

    .hint-body {
      color: var(--hint-body-text);
      line-height: 1.6;
    }

    /* Submit bar */
    .submit-bar {
      position: sticky;
      bottom: 0;
      height: 56px;
      display: flex;
      align-items: center;
      padding: 8px 16px;
      padding-bottom: calc(8px + env(safe-area-inset-bottom));
      background: linear-gradient(to top, var(--surface-translucent-bottom), var(--surface-translucent-top));
      backdrop-filter: blur(8px);
      margin-top: var(--space-6);
    }

    .submit-row {
      display: flex;
      justify-content: flex-end;
      align-items: center;
      gap: var(--space-3);
      width: 100%;
    }

    .submit-row .left {
      margin-right: auto;
    }

    /* Forms */
    .form-input {
      width: 100%;
      padding: var(--space-2) var(--space-3);
      color: var(--color-gray-800);
      border: 1px solid var(--surface-border);
      border-radius: var(--radius-md);
      font-size: var(--font-size-base);
      transition: background .18s ease, border-color .18s ease, box-shadow .18s ease;
      background: var(--surface-raised);
    }

    .form-input:placeholder-shown {
      background: var(--surface-raised);
      border-color: var(--surface-border);
    }

    .form-input:focus {
      outline: none;
      border-color: var(--color-primary);
      box-shadow: 0 0 0 3px var(--focus-ring-subtle);
      background: var(--surface-raised);
    }
    
    .form-input:not(:placeholder-shown):not(:focus) {
      background: color-mix(in srgb, var(--surface-raised) 75%, var(--color-primary-light) 25%);
      border-color: var(--surface-border-strong);
    }

    /* Grid layouts */
    .grid {
      display: grid;
      grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
      gap: var(--space-5);
      margin-top: var(--space-6);
    }

    .row {
      display: flex;
      align-items: center;
      justify-content: space-between;
      gap: var(--space-4);
      margin-bottom: var(--space-6);
    }

    .left {
      display: flex;
      align-items: center;
      gap: var(--space-3);
    }

    .right {
      display: flex;
      align-items: center;
      gap: var(--space-3);
    }

    /* Progress bars in cards */
    .progress-bar {
      width: 100%;
      height: 4px;
      background: var(--color-gray-200);
      border-radius: var(--radius-sm);
      overflow: hidden;
      margin: var(--space-4) 0 var(--space-3) 0;
    }

    .progress-fill {
      height: 100%;
      width: 0%;
      background: var(--color-gray-400);
      border-radius: var(--radius-sm);
      transition: width var(--transition-medium);
    }

    .progress-fill.active {
      background: var(--color-primary);
    }

    .progress-text {
      font-size: var(--font-size-sm);
      color: var(--color-gray-500);
      line-height: 1.4;
    }

    .badge {
      display: inline-flex;
      align-items: center;
      padding: var(--space-1) var(--space-2);
      font-size: var(--font-size-xs);
      font-weight: 500;
      color: var(--color-gray-700);
      background: var(--color-gray-100);
      border-radius: var(--radius-sm);
      margin-left: var(--space-2);
    }

    /* Empty states */
    .empty-state {
      text-align: center;
      padding: var(--space-16) var(--space-4);
      color: var(--color-gray-400);
    }

    .loading {
      opacity: 0.6;
    }

    /* Modals */
    .modal {
      position: fixed;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      z-index: 1000;
      opacity: 0;
      visibility: hidden;
      transition: all var(--transition-medium);
    }

    .modal.open {
      opacity: 1;
      visibility: visible;
    }

    .modal-backdrop {
      position: absolute;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      background: var(--overlay);
      backdrop-filter: blur(4px);
      display: flex;
      align-items: center;
      justify-content: center;
      padding: var(--space-4);
    }

    .modal-content {
      background: var(--surface-raised);
      border: 1px solid var(--surface-border);
      border-radius: var(--radius-lg);
      padding: var(--space-6);
      box-shadow: var(--shadow-medium);
      max-width: 460px;
      width: 100%;
      max-height: 90vh;
      overflow-y: auto;
      position: relative;
    }

    .modal-header {
      display: flex;
      align-items: center;
      justify-content: space-between;
      margin-bottom: var(--space-4);
      border-bottom: 1px solid var(--surface-border);
      padding-bottom: var(--space-3);
    }

    .modal-title {
      font-size: var(--font-size-xl);
      font-weight: 600;
      color: var(--color-gray-900);
    }

    .modal-close {
      background: none;
      border: none;
      cursor: pointer;
      padding: var(--space-1);
      min-width: 40px;
      min-height: 40px;
      color: var(--color-gray-500);
      border-radius: var(--radius-md);
      transition: all var(--transition-fast);
    }

    .modal-close:hover {
      background: var(--surface-muted);
      color: var(--color-gray-700);
    }

    .modal-close:focus-visible {
      outline: none;
      box-shadow: 0 0 0 3px var(--focus-ring-medium);
    }

    .form-group {
      margin-bottom: var(--space-4);
    }

    .form-label {
      display: block;
      font-size: var(--font-size-sm);
      font-weight: 500;
      color: var(--color-gray-700);
      margin-bottom: var(--space-2);
    }

    /* OTP inputs */
    .otp-container {
      display: flex;
      gap: var(--space-2);
      margin-bottom: var(--space-4);
      justify-content: center;
    }

    .otp-input {
      width: 48px;
      height: 48px;
      text-align: center;
      font-size: var(--font-size-lg);
      font-weight: 600;
      color: var(--color-gray-900);
      border: 1px solid var(--surface-border);
      border-radius: var(--radius-md);
      background: var(--surface-raised);
      transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
    }

    .otp-input:focus {
      outline: none;
      border-color: var(--color-primary);
      box-shadow: 0 0 0 3px var(--focus-ring-subtle);
    }

    /* CTA buttons in cards */
    .btn-mini {
      padding: var(--space-1) var(--space-3);
      font-size: var(--font-size-xs);
      font-weight: 500;
      background: var(--surface-muted);
      color: var(--color-gray-600);
      border: 1px solid var(--surface-border);
      border-radius: var(--radius-sm);
      cursor: pointer;
      transition: all var(--transition-fast);
      min-height: 40px;
    }

    .btn-mini:hover {
      background: color-mix(in srgb, var(--surface-muted) 60%, var(--color-white) 40%);
      border-color: var(--surface-border-strong);
    }

    .btn-mini:focus-visible {
      outline: none;
      box-shadow: 0 0 0 3px var(--focus-ring-medium);
    }

    /* Responsive design */
    @media (max-width: 960px) {
      .menu-toggle {
        display: flex;
      }

      .header-content > .nav {
        display: none;
      }
    }

    @media (max-width: 768px) {
      .main {
        padding: var(--space-2) 0 var(--space-12);
      }

      .heading-1 {
        font-size: var(--font-size-2xl);
      }

      .quiz-header {
        grid-template-columns: 1fr;
        gap: var(--space-3);
        text-align: center;
        padding: var(--space-3) 0;
        margin-bottom: var(--space-4);
      }

      .quiz-header .left,
      .quiz-header .right {
        justify-self: center;
        order: 2;
      }

      .quiz-header .center {
        order: 1;
      }

      .question-card {
        padding: var(--space-3);
      }

      .option {
        padding: var(--space-2) var(--space-3);
        gap: var(--space-2);
        min-height: 48px;
      }

      .option-label {
        width: 20px;
        height: 20px;
        font-size: var(--font-size-xs);
      }

      .option-check {
        width: 18px;
        height: 18px;
      }

      .nav {
        gap: var(--space-1);
      }

      .nav-link {
        padding: var(--space-2) var(--space-3);
        font-size: var(--font-size-xs);
      }

      .grid {
        grid-template-columns: 1fr;
        gap: var(--space-4);
      }

      .row {
        flex-direction: column;
        align-items: stretch;
        gap: var(--space-3);
      }

      .submit-row {
        flex-direction: column-reverse;
        gap: var(--space-3);
      }

      .submit-row .left {
        margin-right: 0;
        width: 100%;
      }

      .progress-track {
        width: 120px;
      }

      .progress-compact {
        flex-wrap: wrap;
        gap: var(--space-2);
      }

      .submit-bar {
        height: 60px;
      }
    }

    @media (max-width: 480px) {
      .container {
        padding: 0 var(--space-3);
      }

      .card {
        padding: var(--space-6);
      }

      .question-card {
        padding: var(--space-5);
      }

      .modal-content {
        padding: var(--space-6);
        margin: var(--space-3);
      }

      .otp-container {
        gap: var(--space-1);
      }

      .otp-input {
        width: 44px;
        height: 44px;
      }
    }
    .explanation-slot {
      min-height: 80px;             /* keeps layout stable before submit */
      overflow: hidden;
      transition: max-height 0.3s ease, opacity 0.3s ease;
      max-height: 0;
      opacity: 0;
    }

    .explanation-slot.show {
      max-height: 300px;            /* adjust if you expect longer text */
      opacity: 1;
    }




    /* Dark mode support (automatic based on system preference) */
    @media (prefers-color-scheme: dark) {
      :root {
        --color-gray-50: #060B16;
        --color-gray-100: #0B1222;
        --color-gray-200: #101A2D;
        --color-gray-300: #17253B;
        --color-gray-400: #21324C;
        --color-gray-500: #33435C;
        --color-gray-600: #94A3B8;
        --color-gray-700: #CBD5E1;
        --color-gray-800: #E2E8F0;
        --color-gray-900: #F1F5F9;

        --surface-base: #060B16;
        --surface-raised: #0D1626;
        --surface-muted: #122035;
        --surface-border: rgba(148, 163, 184, 0.18);
        --surface-border-strong: rgba(148, 163, 184, 0.32);

        --color-primary: #60A5FA;
        --color-primary-hover: #7CB7FB;
        --color-primary-light: rgba(96, 165, 250, 0.18);
        --color-primary-lighter: rgba(59, 130, 246, 0.12);
        --color-primary-dark: #1E3A8A;

        --color-success: #4ADE80;
        --color-success-light: rgba(74, 222, 128, 0.16);
        --color-success-bg: rgba(21, 128, 61, 0.25);
        --color-success-text: #BBF7D0;
        --color-error: #F87171;
        --color-error-light: rgba(248, 113, 113, 0.18);
        --color-error-bg: rgba(127, 29, 29, 0.4);
        --color-error-text: #FCA5A5;

        --hint-bg: rgba(37, 99, 235, 0.18);
        --hint-border: rgba(59, 130, 246, 0.35);
        --hint-border-accent: #60A5FA;
        --hint-header-text: #BFDBFE;
        --hint-body-text: #E0F2FE;

        --selection-bg: rgba(96, 165, 250, 0.22);
        --selection-border: #60A5FA;

        --shadow-subtle: 0 1px 4px rgba(2, 6, 17, 0.6);
        --shadow-soft: 0 8px 28px rgba(2, 6, 17, 0.55);
        --shadow-medium: 0 18px 44px rgba(2, 6, 17, 0.6);
        --shadow-card: 0 28px 64px rgba(2, 6, 17, 0.65);
        --shadow-button-hover: 0 10px 28px rgba(96, 165, 250, 0.32);

        --surface-translucent: rgba(6, 12, 24, 0.88);
        --surface-translucent-bottom: rgba(6, 12, 24, 0.92);
        --surface-translucent-top: rgba(6, 12, 24, 0.82);
        --overlay: rgba(2, 6, 17, 0.82);
        --focus-ring: rgba(96, 165, 250, 0.52);
        --focus-ring-subtle: rgba(96, 165, 250, 0.28);
        --focus-ring-medium: rgba(96, 165, 250, 0.36);
      }

      body {
        background: var(--surface-base);
        color: var(--color-gray-600);
      }

      .header {
        background: var(--surface-translucent);
        border-bottom: 1px solid var(--surface-border);
        box-shadow: 0 1px 0 rgba(2, 6, 17, 0.6);
      }

      .card,
      .question-card {
        background: var(--surface-raised);
        border-color: var(--surface-border);
      }

      .card:hover,
      .question-card:hover {
        background: color-mix(in srgb, var(--surface-raised) 80%, rgba(96, 165, 250, 0.2) 20%);
      }

      .option {
        background: var(--surface-muted);
        border-color: var(--surface-border);
      }

      .option:hover:not(.disabled) {
        background: color-mix(in srgb, var(--surface-muted) 70%, rgba(96, 165, 250, 0.16) 30%);
      }

      .btn-secondary {
        background: var(--surface-muted);
        border-color: var(--surface-border);
        color: var(--color-gray-700);
      }

      .btn-secondary:hover {
        background: color-mix(in srgb, var(--surface-muted) 60%, rgba(96, 165, 250, 0.16) 40%);
      }

      .ai-explanation {
        background: var(--surface-muted);
        border: 1px solid var(--surface-border);
      }

      .feedback-body {
        color: var(--color-gray-700);
        background: var(--surface-muted);
      }

      .form-input,
      .otp-input {
        background: var(--surface-muted);
        color: var(--color-gray-800);
        border-color: var(--surface-border);
      }

      .form-input:focus,
      .otp-input:focus {
        border-color: var(--color-primary);
      }

      .form-input:not(:placeholder-shown):not(:focus) {
        background: var(--surface-muted);
        border-color: var(--surface-border-strong);
      }

      .nav-drawer {
        background: var(--surface-raised);
      }
    }