/* ==========================================================================
   RESET & BASE VARIABLES
   ========================================================================== */
:root {
  /* Color Palette - Cyberpunk Neon Dark */
  --bg-base: #08090f;
  --bg-panel: rgba(16, 20, 36, 0.45);
  --bg-panel-solid: #101424;
  --border-color: rgba(255, 255, 255, 0.06);
  --border-glow: rgba(0, 242, 254, 0.3);
  
  --color-primary: #8a2be2;      /* Electric Violet */
  --color-primary-glow: rgba(138, 43, 226, 0.4);
  --color-accent: #00f2fe;       /* Neon Cyan */
  --color-accent-glow: rgba(0, 242, 254, 0.4);
  --color-success: #10b981;      /* Emerald Green */
  --color-success-glow: rgba(16, 185, 129, 0.4);
  --color-danger: #ef4444;       /* Crimson Red */
  --color-danger-glow: rgba(239, 68, 68, 0.4);
  
  --color-text: #f3f4f6;
  --color-text-muted: #9ca3af;
  
  /* Fonts */
  --font-sans: 'Inter', system-ui, -apple-system, sans-serif;
  --font-mono: 'Orbitron', monospace;
  
  /* Transitions */
  --transition-fast: 0.15s ease;
  --transition-normal: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  -webkit-tap-highlight-color: transparent;
}

body {
  background-color: var(--bg-base);
  color: var(--color-text);
  font-family: var(--font-sans);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  overflow-x: hidden;
  position: relative;
}

/* ==========================================================================
   AMBIENT BACKGROUND GLOWS
   ========================================================================== */
.bg-glow {
  position: absolute;
  width: 50vw;
  height: 50vw;
  border-radius: 50%;
  filter: blur(120px);
  opacity: 0.12;
  z-index: -1;
  pointer-events: none;
}

.bg-glow-purple {
  background: radial-gradient(circle, var(--color-primary) 0%, rgba(0,0,0,0) 70%);
  top: -10%;
  left: -10%;
}

.bg-glow-cyan {
  background: radial-gradient(circle, var(--color-accent) 0%, rgba(0,0,0,0) 70%);
  bottom: -10%;
  right: -10%;
}

/* ==========================================================================
   LAYOUT STRUCTURE
   ========================================================================== */
.app-container {
  width: 100%;
  max-width: 960px;
  padding: 24px;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  justify-content: center;
  position: relative;
  z-index: 1;
}

@media (min-width: 1200px) {
  .app-container {
    max-width: 1200px;
  }
}

/* Utility Bar (Mute Toggle) */
.utility-bar {
  position: absolute;
  top: 24px;
  right: 24px;
  z-index: 10;
}

.utility-btn {
  background: rgba(255, 255, 255, 0.03);
  border: 1px solid var(--border-color);
  border-radius: 50%;
  width: 44px;
  height: 44px;
  display: flex;
  justify-content: center;
  align-items: center;
  cursor: pointer;
  color: var(--color-text-muted);
  backdrop-filter: blur(8px);
  transition: all var(--transition-fast);
}

.utility-btn:hover {
  color: var(--color-text);
  background: rgba(255, 255, 255, 0.08);
  border-color: rgba(255, 255, 255, 0.15);
  transform: translateY(-2px);
}

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

.hidden {
  display: none !important;
}

/* ==========================================================================
   SCREENS STATES
   ========================================================================== */
.screen {
  display: none;
  flex-direction: column;
  width: 100%;
  opacity: 0;
  transform: scale(0.98);
  transition: opacity var(--transition-normal), transform var(--transition-normal);
}

.screen.active {
  display: flex;
  opacity: 1;
  transform: scale(1);
}

/* ==========================================================================
   MAIN MENU SCREEN
   ========================================================================== */
#menu-screen {
  align-items: center;
  text-align: center;
  gap: 32px;
}

.menu-header {
  margin-top: 40px;
  margin-bottom: 12px;
}

.logo-text {
  font-family: var(--font-mono);
  font-size: 3rem;
  font-weight: 900;
  letter-spacing: -1px;
  text-transform: uppercase;
  background: linear-gradient(135deg, #fff 0%, #a5b4fc 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  text-shadow: 0 0 40px rgba(138, 43, 226, 0.3);
}

.accent-text {
  background: linear-gradient(135deg, var(--color-accent) 0%, var(--color-primary) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.subtitle {
  color: var(--color-text-muted);
  font-size: 1rem;
  letter-spacing: 4px;
  text-transform: uppercase;
  font-weight: 500;
  margin-top: 8px;
}

.difficulty-section {
  width: 100%;
}

.section-title {
  font-family: var(--font-mono);
  font-size: 0.9rem;
  color: var(--color-text-muted);
  letter-spacing: 3px;
  margin-bottom: 24px;
  text-transform: uppercase;
  font-weight: 700;
}

.difficulty-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 16px;
  width: 100%;
}

@media (min-width: 768px) {
  .difficulty-grid {
    grid-template-columns: repeat(5, 1fr);
  }
}

/* Glassmorphism Cards */
.difficulty-card {
  background: none;
  border: none;
  cursor: pointer;
  text-align: left;
  outline: none;
  transition: transform var(--transition-fast);
}

.card-inner {
  background: var(--bg-panel);
  border: 1px solid var(--border-color);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-radius: 16px;
  padding: 24px;
  height: 100%;
  display: flex;
  flex-direction: column;
  gap: 16px;
  box-shadow: 0 8px 32px 0 rgba(0, 0, 0, 0.2);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast), background var(--transition-fast);
}

.difficulty-card:hover .card-inner {
  border-color: var(--border-glow);
  background: rgba(16, 20, 36, 0.65);
  box-shadow: 0 12px 40px 0 rgba(0, 242, 254, 0.1);
}

.difficulty-card:active {
  transform: scale(0.97);
}

.mode-badge {
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: 0.75rem;
  letter-spacing: 1.5px;
  padding: 4px 10px;
  border-radius: 6px;
  width: fit-content;
  color: #fff;
  text-shadow: 0 1px 2px rgba(0,0,0,0.5);
}

.easy-badge { background: var(--color-success); }
.normal-badge { background: var(--color-accent); color: #08090f; text-shadow: none; }
.hard-badge { background: #f59e0b; } /* Orange */
.expert-badge { background: var(--color-danger); }
.custom-badge { background: var(--color-primary); }

.card-title {
  font-size: 1.15rem;
  font-weight: 600;
  color: var(--color-text);
}

.card-bullets {
  list-style: none;
  font-size: 0.85rem;
  color: var(--color-text-muted);
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.card-bullets li {
  position: relative;
  padding-left: 14px;
}

.card-bullets li::before {
  content: "•";
  position: absolute;
  left: 0;
  color: var(--color-accent);
}

.menu-actions {
  margin-top: 12px;
}

/* ==========================================================================
   BUTTONS
   ========================================================================== */
.primary-btn {
  background: linear-gradient(135deg, var(--color-primary) 0%, #6366f1 100%);
  color: white;
  border: none;
  font-weight: 600;
  font-size: 1rem;
  padding: 14px 28px;
  border-radius: 12px;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  box-shadow: 0 4px 20px var(--color-primary-glow);
  transition: all var(--transition-fast);
}

.primary-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 24px rgba(99, 102, 241, 0.6);
}

.primary-btn:active {
  transform: translateY(1px);
}

.glass-btn {
  background: var(--bg-panel);
  border: 1px solid var(--border-color);
  backdrop-filter: blur(8px);
  box-shadow: 0 4px 16px rgba(0,0,0,0.2);
}

.glass-btn:hover {
  background: rgba(255, 255, 255, 0.06);
  border-color: rgba(255, 255, 255, 0.15);
  box-shadow: 0 6px 20px rgba(0,0,0,0.3);
}

.secondary-btn {
  background: transparent;
  color: var(--color-text);
  border: 1px solid rgba(255, 255, 255, 0.15);
  font-weight: 600;
  font-size: 1rem;
  padding: 14px 28px;
  border-radius: 12px;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.secondary-btn:hover {
  background: rgba(255,255,255,0.05);
  border-color: rgba(255,255,255,0.3);
}

.text-btn {
  background: none;
  border: none;
  color: var(--color-text-muted);
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  transition: color var(--transition-fast);
}

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

/* ==========================================================================
   GAMEPLAY SCREEN
   ========================================================================== */
#game-screen {
  gap: 40px;
  max-width: 640px;
  margin: 0 auto;
}

.game-hud {
  display: flex;
  justify-content: space-between;
  align-items: center;
  width: 100%;
}

.score-display {
  display: flex;
  align-items: center;
  gap: 8px;
}

.score-label {
  font-size: 0.8rem;
  font-family: var(--font-mono);
  color: var(--color-text-muted);
  letter-spacing: 1px;
}

.score-number {
  font-family: var(--font-mono);
  font-weight: 900;
  font-size: 1.8rem;
  color: #fff;
  text-shadow: 0 0 10px rgba(255,255,255,0.3);
}

.game-container {
  background: var(--bg-panel);
  border: 1px solid var(--border-color);
  border-radius: 24px;
  padding: 48px 32px;
  width: 100%;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 32px;
  backdrop-filter: blur(20px);
  box-shadow: 0 16px 48px 0 rgba(0, 0, 0, 0.3);
  position: relative;
  overflow: hidden;
}

.equation-box {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 16px;
  margin-bottom: 8px;
}

.equation {
  font-family: var(--font-mono);
  font-size: 2.8rem;
  font-weight: 700;
  letter-spacing: -1px;
  color: #fff;
}

.equals {
  font-family: var(--font-mono);
  font-size: 2.8rem;
  font-weight: 500;
  color: var(--color-text-muted);
}

/* Form & Inputs */
.answer-form {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 20px;
  width: 100%;
  max-width: 280px;
}

.input-wrapper {
  position: relative;
  width: 100%;
}

#answer-input {
  width: 100%;
  background: rgba(0, 0, 0, 0.35);
  border: 2px solid var(--border-color);
  border-radius: 16px;
  padding: 16px;
  text-align: center;
  font-family: var(--font-mono);
  font-size: 2.2rem;
  font-weight: 700;
  color: #fff;
  outline: none;
  transition: all var(--transition-fast);
  z-index: 2;
  position: relative;
}

#answer-input:focus {
  border-color: var(--color-accent);
  box-shadow: 0 0 20px rgba(0, 242, 254, 0.15);
}

#answer-input::placeholder {
  color: rgba(255, 255, 255, 0.15);
}

.input-glow {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  border-radius: 16px;
  background: radial-gradient(circle, var(--color-accent-glow) 0%, rgba(0,0,0,0) 70%);
  opacity: 0;
  transition: opacity var(--transition-fast);
  z-index: 1;
  pointer-events: none;
}

#answer-input:focus + .input-glow {
  opacity: 0.4;
}

.submit-btn {
  width: 100%;
  background: var(--color-text);
  color: var(--bg-base);
  border: none;
  font-family: var(--font-mono);
  font-weight: 900;
  font-size: 1rem;
  padding: 16px;
  border-radius: 14px;
  cursor: pointer;
  letter-spacing: 2px;
  transition: all var(--transition-fast);
}

.submit-btn:hover {
  background: #fff;
  transform: translateY(-2px);
  box-shadow: 0 4px 20px rgba(255, 255, 255, 0.25);
}

.submit-btn:active {
  transform: translateY(1px);
}

.keyboard-tip {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  letter-spacing: 0.5px;
}

/* Feedback Overlay */
.feedback-overlay {
  position: absolute;
  inset: 0;
  display: flex;
  justify-content: center;
  align-items: center;
  pointer-events: none;
  z-index: 5;
  background: rgba(8, 9, 15, 0.4);
  backdrop-filter: blur(4px);
  animation: fadeIn 0.1s ease-out;
}

.feedback-text {
  font-family: var(--font-mono);
  font-size: 2.5rem;
  font-weight: 900;
  letter-spacing: 2px;
}

.correct-text {
  color: var(--color-success);
  text-shadow: 0 0 20px var(--color-success-glow);
}

/* Animations */
@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  15%, 45%, 75% { transform: translateX(-8px); }
  30%, 60%, 90% { transform: translateX(8px); }
}

.shake {
  animation: shake 0.45s cubic-bezier(.36,.07,.19,.97) both;
}

@keyframes correctFlash {
  0% { box-shadow: 0 0 0 0 rgba(16, 185, 129, 0); }
  20% { box-shadow: 0 0 40px 10px var(--color-success-glow); }
  100% { box-shadow: 0 0 0 0 rgba(16, 185, 129, 0); }
}

.correct-flash {
  animation: correctFlash 0.6s ease-out;
}

/* ==========================================================================
   GAME OVER SCREEN
   ========================================================================== */
#game-over-screen {
  align-items: center;
  max-width: 480px;
  margin: 0 auto;
}

.glass-panel {
  background: var(--bg-panel);
  border: 1px solid var(--border-color);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-radius: 24px;
  padding: 40px 32px;
  box-shadow: 0 16px 48px 0 rgba(0, 0, 0, 0.3);
  width: 100%;
}

.game-over-container {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  gap: 28px;
}

.game-over-title {
  font-family: var(--font-mono);
  font-size: 2.2rem;
  font-weight: 900;
  color: var(--color-danger);
  letter-spacing: 3px;
  text-shadow: 0 0 30px var(--color-danger-glow);
}

.stats-panel {
  width: 100%;
  background: rgba(0,0,0,0.25);
  border: 1px solid var(--border-color);
  border-radius: 16px;
  padding: 16px 24px;
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.stat-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.stat-label {
  color: var(--color-text-muted);
  font-size: 0.9rem;
}

.stat-value {
  font-weight: 600;
  font-size: 1.1rem;
}

.wrong-details-item {
  border-top: 1px solid rgba(255,255,255,0.06);
  padding-top: 12px;
  margin-top: 4px;
}

.text-danger {
  color: var(--color-danger);
  font-family: var(--font-mono);
  font-weight: 700;
}

/* High Score Qualify Panel */
.qualify-panel {
  width: 100%;
  background: rgba(138, 43, 226, 0.08);
  border: 1px dashed var(--color-primary);
  border-radius: 16px;
  padding: 20px;
  display: flex;
  flex-direction: column;
  gap: 16px;
  animation: borderPulse 2s infinite alternate;
}

@keyframes borderPulse {
  0% { border-color: rgba(138, 43, 226, 0.4); }
  100% { border-color: rgba(0, 242, 254, 0.8); }
}

.qualify-header {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
}

.crown-icon {
  font-size: 1.8rem;
  animation: bounce 1s infinite alternate;
}

@keyframes bounce {
  0% { transform: translateY(0); }
  100% { transform: translateY(-4px); }
}

.qualify-header h3 {
  font-family: var(--font-mono);
  font-size: 1.1rem;
  font-weight: 900;
  color: var(--color-accent);
}

.qualify-header p {
  font-size: 0.8rem;
  color: var(--color-text-muted);
  margin-top: 4px;
  line-height: 1.4;
}

.name-entry-form {
  display: flex;
  gap: 10px;
  width: 100%;
}

#player-name {
  flex: 1;
  background: rgba(0,0,0,0.3);
  border: 1px solid var(--border-color);
  border-radius: 10px;
  padding: 10px;
  color: #fff;
  font-family: var(--font-mono);
  font-size: 1.1rem;
  font-weight: 700;
  letter-spacing: 2px;
  text-align: center;
  outline: none;
  text-transform: uppercase;
}

#player-name:focus {
  border-color: var(--color-accent);
}

.submit-name-btn {
  background: var(--color-primary);
  color: white;
  border: none;
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: 0.85rem;
  padding: 0 16px;
  border-radius: 10px;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.submit-name-btn:hover {
  background: #9b4cfb;
}

.error-msg {
  color: var(--color-danger);
  font-size: 0.75rem;
  text-align: center;
}

.game-over-actions {
  display: flex;
  flex-direction: column;
  gap: 12px;
  width: 100%;
}

/* ==========================================================================
   LEADERBOARDS SCREEN
   ========================================================================== */
#leaderboard-screen {
  max-width: 680px;
  margin: 0 auto;
}

.leaderboard-container {
  display: flex;
  flex-direction: column;
  gap: 24px;
}

.leaderboard-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  width: 100%;
}

.leaderboard-header h2 {
  font-family: var(--font-mono);
  font-size: 1.3rem;
  font-weight: 900;
  letter-spacing: 1.5px;
}

.close-btn {
  background: none;
  border: none;
  color: var(--color-text-muted);
  cursor: pointer;
  padding: 4px;
  transition: color var(--transition-fast);
}

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

/* Tabs */
.leaderboard-tabs {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  background: rgba(0,0,0,0.2);
  border: 1px solid var(--border-color);
  border-radius: 10px;
  padding: 4px;
}

.tab-btn {
  background: none;
  border: none;
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--color-text-muted);
  padding: 10px;
  border-radius: 6px;
  cursor: pointer;
  transition: all var(--transition-fast);
}

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

.tab-btn.active {
  background: var(--bg-panel-solid);
  color: var(--color-accent);
  box-shadow: 0 4px 12px rgba(0,0,0,0.25);
}

/* High Scores Table */
.leaderboard-table-wrapper {
  max-height: 400px;
  overflow-y: auto;
  border-radius: 12px;
  background: rgba(0,0,0,0.15);
  border: 1px solid var(--border-color);
}

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

.leaderboard-table th, 
.leaderboard-table td {
  padding: 14px 18px;
}

.leaderboard-table th {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--color-text-muted);
  letter-spacing: 1px;
  background: rgba(0,0,0,0.25);
  position: sticky;
  top: 0;
  z-index: 1;
}

.leaderboard-table tr {
  border-bottom: 1px solid rgba(255,255,255,0.03);
}

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

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

.col-rank { width: 15%; font-family: var(--font-mono); }
.col-name { width: 35%; font-weight: 600; }
.col-score { width: 25%; font-family: var(--font-mono); font-weight: 700; }
.col-date { width: 25%; color: var(--color-text-muted); font-size: 0.8rem; }

.loading-cell,
.empty-cell {
  text-align: center;
  color: var(--color-text-muted);
  padding: 40px 0;
  font-size: 0.9rem;
}

/* Custom Scrollbar for the table */
.leaderboard-table-wrapper::-webkit-scrollbar {
  width: 6px;
}

.leaderboard-table-wrapper::-webkit-scrollbar-track {
  background: transparent;
}

.leaderboard-table-wrapper::-webkit-scrollbar-thumb {
  background: rgba(255, 255, 255, 0.1);
  border-radius: 3px;
}

.leaderboard-table-wrapper::-webkit-scrollbar-thumb:hover {
  background: rgba(255, 255, 255, 0.2);
}

/* ==========================================================================
   CUSTOM SETUP SCREEN
   ========================================================================== */
#custom-setup-screen {
  align-items: center;
  max-width: 500px;
  margin: 0 auto;
}

.custom-setup-container {
  display: flex;
  flex-direction: column;
  align-items: center;
  width: 100%;
}

.custom-setup-header {
  margin-bottom: 24px;
  text-align: center;
}

.custom-setup-header h2 {
  font-family: var(--font-mono);
  font-size: 1.5rem;
  font-weight: 900;
  letter-spacing: 1.5px;
  margin-bottom: 8px;
}

.custom-setup-header p {
  color: var(--color-text-muted);
  font-size: 0.85rem;
}

.custom-setup-form-element {
  display: flex;
  flex-direction: column;
  gap: 20px;
  width: 100%;
}

.form-group {
  display: flex;
  flex-direction: column;
  gap: 8px;
  width: 100%;
}

.form-group label,
.form-group span {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--color-text-muted);
  letter-spacing: 1px;
}

.custom-setup-form-element input[type="number"] {
  width: 100%;
  background: rgba(0, 0, 0, 0.35);
  border: 2px solid var(--border-color);
  border-radius: 12px;
  padding: 14px;
  color: #fff;
  font-family: var(--font-mono);
  font-size: 1.1rem;
  outline: none;
  transition: all var(--transition-fast);
}

.custom-setup-form-element input[type="number"]:focus {
  border-color: var(--color-accent);
  box-shadow: 0 0 15px rgba(0, 242, 254, 0.15);
  background: rgba(0, 0, 0, 0.45);
}

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

.operator-checkbox-label {
  cursor: pointer;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  background: rgba(255, 255, 255, 0.02);
  border: 1px solid var(--border-color);
  padding: 16px;
  border-radius: 12px;
  transition: all var(--transition-fast);
  user-select: none;
}

.operator-checkbox-label:hover {
  background: rgba(255, 255, 255, 0.06);
  border-color: rgba(255, 255, 255, 0.15);
  transform: translateY(-2px);
}

.operator-checkbox-label:active {
  transform: translateY(0);
}

.operator-checkbox-label.selected {
  border-color: var(--color-accent) !important;
  background: rgba(0, 242, 254, 0.08) !important;
  box-shadow: 0 0 15px rgba(0, 242, 254, 0.2);
}

.operator-checkbox-label .operator-icon {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--color-text-muted);
  transition: all var(--transition-fast);
}

.operator-checkbox-label .operator-name {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  transition: all var(--transition-fast);
}

.operator-checkbox-label.selected .operator-icon {
  color: var(--color-accent) !important;
  text-shadow: 0 0 10px var(--color-accent-glow);
}

.operator-checkbox-label.selected .operator-name {
  color: var(--color-text) !important;
  font-weight: 600;
}

.custom-setup-form-element select {
  width: 100%;
  background: var(--bg-panel-solid);
  border: 1px solid var(--border-color);
  border-radius: 12px;
  padding: 14px;
  color: #fff;
  font-family: var(--font-sans);
  font-size: 1rem;
  outline: none;
  transition: all var(--transition-fast);
  cursor: pointer;
  appearance: none;
  -webkit-appearance: none;
  background-image: url("data:image/svg+xml;charset=utf-8,%3Csvg xmlns='http://www.w3.org/2000/svg' fill='none' viewBox='0 0 24 24' stroke='white'%3E%3Cpath stroke-linecap='round' stroke-linejoin='round' stroke-width='2' d='M19 9l-7 7-7-7'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 14px center;
  background-size: 16px;
  padding-right: 40px;
}

.custom-setup-form-element select:focus {
  border-color: var(--color-accent);
  box-shadow: 0 0 15px rgba(0, 242, 254, 0.15);
}

.setup-actions {
  margin-top: 12px;
  display: flex;
  flex-direction: column;
  gap: 12px;
  width: 100%;
}

.toggle-checkbox-label {
  cursor: pointer;
  display: flex;
  flex-direction: row;
  align-items: center;
  justify-content: flex-start;
  gap: 12px;
  background: rgba(255, 255, 255, 0.02);
  border: 1px solid var(--border-color);
  padding: 14px 16px;
  border-radius: 12px;
  transition: all var(--transition-fast);
  user-select: none;
  width: 100%;
}

.toggle-checkbox-label:hover {
  background: rgba(255, 255, 255, 0.06);
  border-color: rgba(255, 255, 255, 0.15);
}

.toggle-checkbox-label.selected {
  border-color: var(--color-accent) !important;
  background: rgba(0, 242, 254, 0.04) !important;
}

.checkbox-indicator {
  width: 20px;
  height: 20px;
  border: 2px solid var(--border-color);
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.85rem;
  color: transparent;
  transition: all var(--transition-fast);
  flex-shrink: 0;
}

.toggle-checkbox-label.selected .checkbox-indicator {
  border-color: var(--color-accent) !important;
  background: var(--color-accent) !important;
  color: #08090f !important;
  box-shadow: 0 0 10px rgba(0, 242, 254, 0.3);
}

.toggle-checkbox-label.selected span:last-child {
  color: var(--color-text) !important;
  font-weight: 500;
}

/* ==========================================================================
   RESPONSIVENESS & MEDIA QUERIES
   ========================================================================== */
@media (max-width: 640px) {
  .logo-text {
    font-size: 2.2rem;
  }
  
  .subtitle {
    font-size: 0.8rem;
    letter-spacing: 2px;
  }
  
  .difficulty-grid {
    grid-template-columns: 1fr;
  }
  
  .equation {
    font-size: 2.2rem;
  }
  
  .equals {
    font-size: 2.2rem;
  }
  
  #answer-input {
    font-size: 1.8rem;
    padding: 12px;
  }
  
  .leaderboard-table th, 
  .leaderboard-table td {
    padding: 10px 12px;
    font-size: 0.85rem;
  }
  
  .col-date {
    display: none; /* Hide date on small mobile to fit columns */
  }
  
  .glass-panel,
  .game-container {
    padding: 24px 16px;
  }
}