/* ==========================================================================
   HSCScience Multiplayer Lobby — Professional Stylesheet
   Gimkit/Blooket-quality polish with glass-morphism, micro-interactions,
   and mobile-first responsive design.
   ========================================================================== */

/* --------------------------------------------------------------------------
   CSS Variables
   -------------------------------------------------------------------------- */
:root {
  --primary: #059669;
  --primary-light: #34d399;
  --primary-dark: #047857;
  --secondary: #0ea5e9;
  --accent: #8b5cf6;
  --danger: #ef4444;
  --warning: #f59e0b;
  --success: #22c55e;

  --bg: #0b1120;
  --bg-elevated: #1e293b;
  --surface: #111827;
  --card: rgba(30, 41, 59, 0.7);
  --card-hover: rgba(38, 53, 72, 0.8);
  --border: rgba(255, 255, 255, 0.08);
  --border-focus: #059669;

  --text: #f1f5f9;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;

  --gradient-primary: linear-gradient(135deg, #059669, #0ea5e9);
  --gradient-gold: linear-gradient(135deg, #f59e0b, #fbbf24);
  --gradient-silver: linear-gradient(135deg, #94a3b8, #cbd5e1);
  --gradient-bronze: linear-gradient(135deg, #b45309, #d97706);
  --gradient-danger: linear-gradient(135deg, #ef4444, #f97316);

  --shadow-card: 0 4px 16px rgba(0, 0, 0, 0.3);
  --shadow-elevated: 0 8px 32px rgba(0, 0, 0, 0.4);
  --shadow-glow-primary: 0 0 20px rgba(5, 150, 105, 0.3);
  --shadow-glow-warning: 0 0 20px rgba(245, 158, 11, 0.3);

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;

  --transition-fast: 0.15s ease;
  --transition-normal: 0.3s ease;
  --transition-slow: 0.5s ease;
}

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

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

body {
  font-family: 'Segoe UI', system-ui, -apple-system, BlinkMacSystemFont, Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
  min-height: 100vh;
  background-image:
    radial-gradient(ellipse 80% 50% at 50% -20%, rgba(5, 150, 105, 0.08), transparent),
    radial-gradient(ellipse 60% 40% at 80% 100%, rgba(14, 165, 233, 0.06), transparent);
}

/* Scrollbar */
::-webkit-scrollbar { width: 8px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: #334155; border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: #475569; }

/* Selection */
::selection {
  background: rgba(5, 150, 105, 0.3);
  color: var(--text);
}

/* --------------------------------------------------------------------------
   App Wrapper
   -------------------------------------------------------------------------- */
#app {
  max-width: 1200px;
  margin: 0 auto;
  padding: 1.5rem;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  justify-content: center;
}

/* --------------------------------------------------------------------------
   Header / Logo area
   -------------------------------------------------------------------------- */
.lobby-header {
  text-align: center;
  margin-bottom: 2rem;
  animation: fadeInDown 0.5s cubic-bezier(0.16, 1, 0.3, 1) both;
}

.lobby-header h1 {
  font-size: clamp(1.75rem, 4vw, 2.5rem);
  font-weight: 800;
  letter-spacing: -0.02em;
  background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 50%, var(--accent) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  filter: drop-shadow(0 2px 4px rgba(5, 150, 105, 0.2));
}

.lobby-header p {
  color: var(--text-secondary);
  margin-top: 0.5rem;
  font-size: 1rem;
  animation: fadeIn 0.5s 0.15s both;
}

/* --------------------------------------------------------------------------
   Panel Grid Layout
   -------------------------------------------------------------------------- */
.lobby-panels {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.5rem;
  animation: fadeInUp 0.5s 0.1s cubic-bezier(0.16, 1, 0.3, 1) both;
}

/* --------------------------------------------------------------------------
   Lobby Panel (card) — Glass-morphism
   -------------------------------------------------------------------------- */
.lobby-panel {
  background: var(--card);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  box-shadow: var(--shadow-card);
  transition: box-shadow var(--transition-normal), transform var(--transition-normal), border-color var(--transition-normal);
  position: relative;
  overflow: hidden;
}

.lobby-panel::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: var(--gradient-primary);
  opacity: 0.6;
  transition: opacity var(--transition-normal);
}

.lobby-panel:hover {
  box-shadow: var(--shadow-elevated), var(--shadow-glow-primary);
  transform: translateY(-2px);
  border-color: rgba(5, 150, 105, 0.25);
}

.lobby-panel:hover::before {
  opacity: 1;
}

.lobby-panel h2 {
  font-size: 1.25rem;
  font-weight: 700;
  margin-bottom: 1.25rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.lobby-panel h2 .icon {
  font-size: 1.5rem;
}

/* --------------------------------------------------------------------------
   Form Elements
   -------------------------------------------------------------------------- */
.form-group {
  margin-bottom: 1.25rem;
}

.form-group label {
  display: block;
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: 0.5rem;
}

.form-group label .required {
  color: var(--danger);
  margin-left: 0.25rem;
}

input[type="text"],
input[type="number"],
input[type="tel"],
select {
  width: 100%;
  background: var(--bg);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 0.75rem 1rem;
  font-size: 1rem;
  font-family: inherit;
  outline: none;
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast), background var(--transition-fast);
}

input[type="text"]::placeholder,
input[type="number"]::placeholder,
input[type="tel"]::placeholder {
  color: var(--text-muted);
}

input[type="text"]:focus,
input[type="number"]:focus,
input[type="tel"]:focus,
select:focus {
  box-shadow: 0 0 0 3px rgba(5, 150, 105, 0.2);
  border-color: var(--primary-light);
  background: rgba(5, 150, 105, 0.03);
}

/* Error states */
input.error,
select.error {
  border-color: var(--danger);
  color: var(--danger);
  animation: shake 0.4s ease;
}

input.error:focus,
select.error:focus {
  box-shadow: 0 0 0 3px rgba(239, 68, 68, 0.2);
  border-color: var(--danger);
}

.error-text {
  color: var(--danger);
  font-size: 0.875rem;
  margin-top: 0.375rem;
  display: flex;
  align-items: center;
  gap: 0.25rem;
  animation: fadeIn 0.2s ease;
}

/* --------------------------------------------------------------------------
   Subject Checkboxes — Colored borders, animated checkmark
   -------------------------------------------------------------------------- */
.subject-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 0.75rem;
}

.subject-checkbox {
  position: relative;
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.75rem 1rem;
  background: rgba(255, 255, 255, 0.02);
  border: 2px solid var(--border);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: border-color var(--transition-fast), background var(--transition-fast), transform var(--transition-fast);
}

.subject-checkbox:hover {
  background: rgba(5, 150, 105, 0.05);
  transform: translateX(2px);
}

/* Subject-specific border colors (applied via inline style or class) */
.subject-checkbox[data-subject="biology"] { border-left-color: #22c55e; }
.subject-checkbox[data-subject="chemistry"] { border-left-color: #3b82f6; }
.subject-checkbox[data-subject="physics"] { border-left-color: #a855f7; }
.subject-checkbox[data-subject="earth"] { border-left-color: #f97316; }
.subject-checkbox[data-subject="astronomy"] { border-left-color: #0ea5e9; }

.subject-checkbox input[type="checkbox"] {
  position: absolute;
  opacity: 0;
  width: 0;
  height: 0;
}

.subject-checkbox .check-box {
  width: 22px;
  height: 22px;
  min-width: 22px;
  border: 2px solid var(--text-muted);
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition-fast);
}

.subject-checkbox .check-box svg {
  width: 12px;
  height: 12px;
  stroke: #fff;
  stroke-width: 3;
  fill: none;
  stroke-linecap: round;
  stroke-linejoin: round;
  opacity: 0;
  transform: scale(0.5) rotate(-45deg);
  transition: all 0.25s cubic-bezier(0.34, 1.56, 0.64, 1);
}

.subject-checkbox input[type="checkbox"]:checked + .check-box {
  background: var(--primary);
  border-color: var(--primary);
  box-shadow: 0 0 8px rgba(5, 150, 105, 0.3);
}

.subject-checkbox input[type="checkbox"]:checked + .check-box svg {
  opacity: 1;
  transform: scale(1) rotate(0deg);
}

.subject-checkbox .subject-label {
  font-weight: 500;
  font-size: 0.9375rem;
}

.subject-checkbox .subject-colour {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  margin-left: auto;
  box-shadow: 0 0 6px currentColor;
}

/* --------------------------------------------------------------------------
   Module Multi-select
   -------------------------------------------------------------------------- */
.module-section {
  margin-bottom: 1rem;
}

.module-section-title {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: 0.5rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.module-section-title .colour-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  box-shadow: 0 0 4px currentColor;
}

.module-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 0.5rem;
}

.module-checkbox {
  position: relative;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.5rem 0.75rem;
  background: rgba(255, 255, 255, 0.02);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 0.875rem;
  transition: border-color var(--transition-fast), background var(--transition-fast);
}

.module-checkbox:hover {
  border-color: var(--secondary);
  background: rgba(14, 165, 233, 0.05);
}

.module-checkbox input[type="checkbox"] {
  position: absolute;
  opacity: 0;
  width: 0;
  height: 0;
}

.module-checkbox .check-box {
  width: 16px;
  height: 16px;
  min-width: 16px;
  border: 2px solid var(--text-muted);
  border-radius: 4px;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition-fast);
}

.module-checkbox .check-box svg {
  width: 10px;
  height: 10px;
  stroke: #fff;
  stroke-width: 3;
  fill: none;
  stroke-linecap: round;
  stroke-linejoin: round;
  opacity: 0;
  transform: scale(0.5);
  transition: all 0.2s cubic-bezier(0.34, 1.56, 0.64, 1);
}

.module-checkbox input[type="checkbox"]:checked + .check-box {
  background: var(--secondary);
  border-color: var(--secondary);
}

.module-checkbox input[type="checkbox"]:checked + .check-box svg {
  opacity: 1;
  transform: scale(1);
}

/* --------------------------------------------------------------------------
   Buttons — Gradient + Shimmer
   -------------------------------------------------------------------------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.875rem 1.5rem;
  border-radius: var(--radius-md);
  font-weight: 600;
  font-size: 1rem;
  font-family: inherit;
  cursor: pointer;
  border: none;
  outline: none;
  transition: all var(--transition-fast);
  width: 100%;
  position: relative;
  overflow: hidden;
  min-height: 44px;
}

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

.btn::after {
  content: '';
  position: absolute;
  top: 0;
  left: -100%;
  width: 100%;
  height: 100%;
  background: linear-gradient(90deg, transparent, rgba(255,255,255,0.15), transparent);
  transition: left 0.5s ease;
}

.btn:hover:not(:disabled)::after {
  left: 100%;
}

.btn-primary {
  background: var(--gradient-primary);
  color: #fff;
  box-shadow: 0 4px 16px rgba(5, 150, 105, 0.3);
}

.btn-primary:hover:not(:disabled) {
  filter: brightness(1.1);
  transform: translateY(-2px);
  box-shadow: 0 6px 24px rgba(5, 150, 105, 0.4);
}

.btn-primary:active:not(:disabled) {
  transform: translateY(0);
  filter: brightness(0.95);
}

.btn-secondary {
  background: linear-gradient(135deg, #0ea5e9, #38bdf8);
  color: #fff;
  box-shadow: 0 4px 16px rgba(14, 165, 233, 0.25);
}

.btn-secondary:hover:not(:disabled) {
  filter: brightness(1.1);
  transform: translateY(-2px);
  box-shadow: 0 6px 24px rgba(14, 165, 233, 0.35);
}

.btn-danger {
  background: var(--gradient-danger);
  color: #fff;
  box-shadow: 0 4px 16px rgba(239, 68, 68, 0.25);
}

.btn-danger:hover:not(:disabled) {
  filter: brightness(1.1);
  transform: translateY(-2px);
  box-shadow: 0 6px 24px rgba(239, 68, 68, 0.35);
}

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

.btn-ghost:hover:not(:disabled) {
  background: rgba(255, 255, 255, 0.05);
  color: var(--text);
  border-color: var(--text-secondary);
}

.btn-icon {
  width: auto;
  padding: 0.5rem;
  aspect-ratio: 1;
}

/* --------------------------------------------------------------------------
   Waiting Room
   -------------------------------------------------------------------------- */
.waiting-room {
  background: var(--card);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 2rem;
  box-shadow: var(--shadow-elevated);
  max-width: 600px;
  margin: 0 auto;
  text-align: center;
  animation: fadeInUp 0.5s cubic-bezier(0.16, 1, 0.3, 1) both;
  position: relative;
  overflow: hidden;
}

.waiting-room::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: var(--gradient-primary);
}

.waiting-room h2 {
  font-size: 1.5rem;
  font-weight: 700;
  margin-bottom: 1.5rem;
}

.waiting-room .room-info {
  margin-bottom: 2rem;
}

/* Room Code — Large monospace with copy tooltip */
.room-label {
  font-size: 0.75rem;
  color: var(--text-secondary);
  margin-bottom: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.15em;
  font-weight: 700;
}

.room-code {
  font-family: 'SF Mono', Monaco, 'Cascadia Code', 'Roboto Mono', Consolas, monospace;
  font-size: clamp(2rem, 5vw, 3.5rem);
  font-weight: 700;
  letter-spacing: 0.15em;
  color: var(--primary-light);
  background: rgba(0, 0, 0, 0.3);
  border: 2px dashed var(--border);
  border-radius: var(--radius-md);
  padding: 1rem 1.5rem;
  display: inline-flex;
  align-items: center;
  gap: 1rem;
  user-select: all;
  cursor: pointer;
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast), color var(--transition-fast);
  position: relative;
  text-shadow: 0 0 20px rgba(52, 211, 153, 0.2);
}

.room-code:hover {
  border-color: var(--primary-light);
  box-shadow: 0 0 24px rgba(5, 150, 105, 0.15);
  color: #fff;
}

.room-code .copy-btn {
  background: rgba(255, 255, 255, 0.05);
  border: 1px solid var(--border);
  color: var(--text-secondary);
  cursor: pointer;
  padding: 0.5rem;
  border-radius: var(--radius-sm);
  transition: all var(--transition-fast);
  position: relative;
  font-size: 1rem;
}

.room-code .copy-btn:hover {
  color: var(--text);
  background: rgba(255, 255, 255, 0.1);
  border-color: var(--text-secondary);
}

.room-code .copy-btn.copied {
  color: var(--success);
  border-color: var(--success);
}

/* Copy tooltip */
.room-code .copy-btn::after {
  content: 'Copied!';
  position: absolute;
  bottom: calc(100% + 6px);
  left: 50%;
  transform: translateX(-50%) translateY(4px);
  background: var(--success);
  color: #fff;
  font-size: 0.7rem;
  font-weight: 700;
  padding: 0.25rem 0.5rem;
  border-radius: 4px;
  opacity: 0;
  pointer-events: none;
  transition: all 0.2s ease;
  white-space: nowrap;
  font-family: 'Segoe UI', system-ui, sans-serif;
  letter-spacing: 0;
}

.room-code .copy-btn.copied::after {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
}

/* Player Count — Dynamic color */
.player-count {
  font-size: 0.9375rem;
  color: var(--text-secondary);
  margin-bottom: 1.5rem;
  font-weight: 500;
}

.player-count .count-highlight {
  color: var(--text);
  font-weight: 700;
}

/* Enough players */
.player-count.ready {
  color: var(--success);
}

.player-count.ready .count-highlight {
  color: var(--success);
  text-shadow: 0 0 10px rgba(34, 197, 94, 0.3);
}

/* Waiting for more */
.player-count.waiting {
  color: var(--warning);
}

.player-count.waiting .count-highlight {
  color: var(--warning);
}

/* Player List */
.player-list {
  list-style: none;
  padding: 0;
  margin: 0 0 2rem 0;
  max-height: 300px;
  overflow-y: auto;
  text-align: left;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  background: rgba(0, 0, 0, 0.2);
}

/* Player Item — Avatar with gradient border, slide-in */
.player-item {
  display: flex;
  align-items: center;
  gap: 0.875rem;
  padding: 0.875rem 1rem;
  border-bottom: 1px solid var(--border);
  animation: slideInLeft 0.35s cubic-bezier(0.16, 1, 0.3, 1) both;
  transition: background var(--transition-fast);
}

.player-item:last-child {
  border-bottom: none;
}

.player-item:hover {
  background: rgba(255, 255, 255, 0.03);
}

.player-item:nth-child(1) { animation-delay: 0.05s; }
.player-item:nth-child(2) { animation-delay: 0.1s; }
.player-item:nth-child(3) { animation-delay: 0.15s; }
.player-item:nth-child(4) { animation-delay: 0.2s; }
.player-item:nth-child(5) { animation-delay: 0.25s; }
.player-item:nth-child(6) { animation-delay: 0.3s; }
.player-item:nth-child(7) { animation-delay: 0.35s; }
.player-item:nth-child(8) { animation-delay: 0.4s; }

/* Avatar with gradient border */
.player-item .player-avatar {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 0.875rem;
  color: #fff;
  flex-shrink: 0;
  position: relative;
  box-shadow: 0 2px 8px rgba(5, 150, 105, 0.2);
}

.player-item .player-avatar::after {
  content: '';
  position: absolute;
  inset: -2px;
  border-radius: 50%;
  background: var(--gradient-primary);
  z-index: -1;
  opacity: 0.4;
}

.player-item .player-name {
  font-weight: 600;
  font-size: 0.9375rem;
}

.player-item .player-tag {
  font-size: 0.7rem;
  padding: 0.2rem 0.6rem;
  border-radius: 9999px;
  background: var(--primary);
  color: #fff;
  font-weight: 700;
  margin-left: auto;
  flex-shrink: 0;
  letter-spacing: 0.02em;
  text-transform: uppercase;
}

.player-item .player-tag.host {
  background: var(--warning);
  color: #000;
}

.player-item .player-tag.you {
  background: var(--secondary);
}

.player-item.removing {
  animation: slideOutRight 0.25s ease both;
}

/* Start Game Button — Pulsing glow when enabled */
.btn-start-game {
  background: var(--gradient-primary);
  color: #fff;
  font-size: 1.125rem;
  font-weight: 700;
  padding: 1rem 2rem;
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-glow-primary);
  animation: pulseGlow 2s ease-in-out infinite;
  min-height: 52px;
}

.btn-start-game:hover:not(:disabled) {
  filter: brightness(1.15);
  transform: translateY(-2px);
}

.btn-start-game:disabled {
  animation: none;
  box-shadow: none;
  opacity: 0.4;
}

@keyframes pulseGlow {
  0%, 100% {
    box-shadow: 0 0 16px rgba(5, 150, 105, 0.3), 0 0 32px rgba(5, 150, 105, 0.1);
  }
  50% {
    box-shadow: 0 0 24px rgba(5, 150, 105, 0.5), 0 0 48px rgba(5, 150, 105, 0.2);
  }
}

/* Waiting message for clients */
.waiting-message {
  color: var(--text-secondary);
  font-size: 1.125rem;
  margin: 2rem 0;
}

.waiting-message .spinner {
  display: inline-block;
  width: 20px;
  height: 20px;
  border: 2px solid var(--border);
  border-top-color: var(--secondary);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
  margin-right: 0.75rem;
  vertical-align: middle;
}

/* --------------------------------------------------------------------------
   Error Banner
   -------------------------------------------------------------------------- */
.error-banner {
  position: fixed;
  top: 1rem;
  left: 50%;
  transform: translateX(-50%) translateY(-100px);
  background: var(--danger);
  color: #fff;
  padding: 0.875rem 1.5rem;
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-elevated), 0 0 20px rgba(239, 68, 68, 0.3);
  font-weight: 600;
  font-size: 0.9375rem;
  z-index: 1000;
  display: flex;
  align-items: center;
  gap: 0.75rem;
  max-width: 90vw;
  width: max-content;
  opacity: 0;
  pointer-events: none;
  transition: transform var(--transition-normal), opacity var(--transition-normal);
}

.error-banner.visible {
  transform: translateX(-50%) translateY(0);
  opacity: 1;
  pointer-events: auto;
}

.error-banner .error-icon {
  font-size: 1.25rem;
  flex-shrink: 0;
}

/* --------------------------------------------------------------------------
   Game Container
   -------------------------------------------------------------------------- */
#game-container {
  width: 100%;
  max-width: 900px;
  margin: 0 auto;
  animation: fadeIn 0.4s ease both;
}

/* --------------------------------------------------------------------------
   Utility Classes
   -------------------------------------------------------------------------- */
.hidden { display: none !important; }

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.text-center { text-align: center; }
.text-muted { color: var(--text-secondary); }

.mt-1 { margin-top: 0.5rem; }
.mt-2 { margin-top: 1rem; }
.mt-3 { margin-top: 1.5rem; }
.mb-1 { margin-bottom: 0.5rem; }
.mb-2 { margin-bottom: 1rem; }
.mb-3 { margin-bottom: 1.5rem; }

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

@keyframes fadeInDown {
  from { opacity: 0; transform: translateY(-20px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes slideInLeft {
  from { opacity: 0; transform: translateX(-30px); }
  to { opacity: 1; transform: translateX(0); }
}

@keyframes slideOutRight {
  from { opacity: 1; transform: translateX(0); }
  to { opacity: 0; transform: translateX(30px); }
}

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

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

/* --------------------------------------------------------------------------
   Panel Transitions
   -------------------------------------------------------------------------- */
.panel-transition-enter {
  animation: fadeInUp 0.3s ease both;
}

.panel-transition-exit {
  animation: fadeOutDown 0.3s ease both;
}

@keyframes fadeOutDown {
  from { opacity: 1; transform: translateY(0); }
  to { opacity: 0; transform: translateY(20px); }
}

/* --------------------------------------------------------------------------
   Back Button
   -------------------------------------------------------------------------- */
.back-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: none;
  border: none;
  color: var(--text-secondary);
  font-size: 0.875rem;
  font-weight: 600;
  cursor: pointer;
  padding: 0.5rem;
  margin-bottom: 1rem;
  border-radius: var(--radius-sm);
  transition: color var(--transition-fast), background var(--transition-fast);
  min-height: 44px;
}

.back-btn:hover {
  color: var(--text);
  background: rgba(255, 255, 255, 0.05);
}

/* --------------------------------------------------------------------------
   Divider
   -------------------------------------------------------------------------- */
.divider {
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--border), transparent);
  margin: 1.5rem 0;
}

/* --------------------------------------------------------------------------
   Info text
   -------------------------------------------------------------------------- */
.info-text {
  font-size: 0.875rem;
  color: var(--text-secondary);
  line-height: 1.5;
}

/* --------------------------------------------------------------------------
   PeerJS Error Fallback
   -------------------------------------------------------------------------- */
.peerjs-error {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
  padding: 2rem;
  text-align: center;
}

.peerjs-error .error-card {
  background: var(--card);
  backdrop-filter: blur(12px);
  border: 1px solid var(--danger);
  border-radius: var(--radius-lg);
  padding: 2rem;
  max-width: 400px;
  box-shadow: var(--shadow-elevated);
}

.peerjs-error .error-card h2 {
  color: var(--danger);
  margin-bottom: 1rem;
}

.peerjs-error .error-card p {
  color: var(--text-secondary);
}

/* --------------------------------------------------------------------------
   Mobile Overhaul
   -------------------------------------------------------------------------- */
@media (max-width: 768px) {
  .lobby-panels {
    grid-template-columns: 1fr;
    gap: 1rem;
  }

  #app {
    padding: 1rem;
    justify-content: flex-start;
    padding-top: 1.5rem;
  }

  .lobby-panel {
    padding: 1.25rem;
    border-radius: var(--radius-md);
  }

  .btn {
    min-height: 48px;
    font-size: 1rem;
  }

  .btn-start-game {
    min-height: 52px;
    font-size: 1.1rem;
  }

  .waiting-room {
    padding: 1.5rem;
    max-width: 100%;
  }

  .room-code {
    font-size: clamp(1.5rem, 8vw, 2.5rem);
    padding: 0.75rem 1rem;
  }

  .player-list {
    max-height: 240px;
  }

  .player-item {
    padding: 0.75rem 0.875rem;
  }

  .player-item .player-avatar {
    width: 36px;
    height: 36px;
  }

  .error-banner {
    font-size: 0.875rem;
    padding: 0.75rem 1rem;
    width: 90vw;
  }

  .subject-grid {
    gap: 0.5rem;
  }

  .module-grid {
    grid-template-columns: 1fr;
  }
}

/* Extra small screens */
@media (max-width: 375px) {
  #app {
    padding: 0.75rem;
  }

  .lobby-panels {
    gap: 0.75rem;
  }

  .lobby-panel {
    padding: 1rem;
  }

  .lobby-panel h2 {
    font-size: 1.1rem;
  }

  .room-code {
    font-size: 1.5rem;
    letter-spacing: 0.1em;
  }

  .waiting-room {
    padding: 1rem;
  }

  .subject-grid {
    grid-template-columns: 1fr;
  }

  .btn {
    padding: 0.75rem 1rem;
    font-size: 0.9375rem;
  }
}

/* Compact leaderboard bar on mobile */
.leaderboard-compact {
  display: none;
}

@media (max-width: 768px) {
  .leaderboard-compact {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.5rem 0.75rem;
    background: var(--card);
    backdrop-filter: blur(12px);
    border: 1px solid var(--border);
    border-radius: var(--radius-md);
    margin-bottom: 0.75rem;
    font-size: 0.8rem;
    overflow-x: auto;
  }

  .leaderboard-compact .lb-compact-title {
    font-weight: 700;
    color: var(--text-secondary);
    flex-shrink: 0;
  }

  .leaderboard-compact .lb-compact-item {
    display: flex;
    align-items: center;
    gap: 0.25rem;
    padding: 0.2rem 0.5rem;
    background: rgba(255,255,255,0.03);
    border-radius: 4px;
    white-space: nowrap;
  }
}

/* --------------------------------------------------------------------------
   Shop Bottom Sheet (mobile-friendly overlay)
   -------------------------------------------------------------------------- */
.shop-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  backdrop-filter: blur(4px);
  -webkit-backdrop-filter: blur(4px);
  z-index: 50;
  opacity: 0;
  pointer-events: none;
  transition: opacity var(--transition-normal);
}

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

.shop-bottom-sheet {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  background: var(--bg-elevated);
  border-radius: var(--radius-lg) var(--radius-lg) 0 0;
  border-top: 2px solid var(--primary);
  padding: 1.5rem;
  z-index: 51;
  transform: translateY(100%);
  transition: transform 0.35s cubic-bezier(0.16, 1, 0.3, 1);
  max-height: 70vh;
  overflow-y: auto;
  box-shadow: 0 -8px 40px rgba(0, 0, 0, 0.5);
}

.shop-bottom-sheet.active {
  transform: translateY(0);
}

.shop-bottom-sheet::before {
  content: '';
  display: block;
  width: 40px;
  height: 4px;
  background: var(--text-muted);
  border-radius: 2px;
  margin: 0 auto 1rem auto;
  opacity: 0.5;
}

/* Pull handle for bottom sheet */
.sheet-handle {
  width: 40px;
  height: 4px;
  background: var(--text-muted);
  border-radius: 2px;
  margin: 0 auto 0.75rem;
  opacity: 0.4;
}