/* ============================================================
   Redox Training Space - Styles
   Based on Diego's mockup design (dark green gradient + mint accents)
   ============================================================ */

/* CSS Variables */
:root {
  --bg-primary: #1a2e2a;
  --bg-secondary: #243d38;
  --bg-card: #2a4a43;
  --bg-card-light: #d4f0e7;
  --bg-input: #e8f8f2;
  --accent-green: #4ade80;
  --accent-mint: #a8e6cf;
  --accent-teal: #2dd4bf;
  --accent-orange: #f59e0b;
  --accent-purple: #8b5cf6;
  --accent-red: #ef4444;
  --accent-blue: #3b82f6;
  --text-primary: #ffffff;
  --text-secondary: #94a3b8;
  --text-dark: #1e293b;
  --text-muted: #64748b;
  --oxidation-color: #ef4444;
  --reduction-color: #22c55e;
  --success-color: #22c55e;
  --error-color: #ef4444;
  --warning-color: #f59e0b;
  --border-radius: 12px;
  --border-radius-sm: 8px;
  --shadow: 0 4px 20px rgba(0,0,0,0.3);
  --shadow-sm: 0 2px 8px rgba(0,0,0,0.2);
  --transition: all 0.3s ease;
}

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

body {
  font-family: 'Inter', 'Segoe UI', system-ui, -apple-system, sans-serif;
  background: linear-gradient(135deg, var(--bg-primary) 0%, var(--bg-secondary) 50%, #1a3530 100%);
  color: var(--text-primary);
  min-height: 100vh;
  line-height: 1.6;
}

/* Typography */
h1, h2, h3 {
  font-weight: 700;
  line-height: 1.2;
}

h1 { font-size: 2rem; }
h2 { font-size: 1.5rem; }
h3 { font-size: 1.2rem; }

/* ============================================================
   Layout
   ============================================================ */

.app-container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 1rem;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

.app-header {
  text-align: center;
  padding: 1.5rem 0;
  border-bottom: 1px solid rgba(255,255,255,0.1);
  margin-bottom: 1.5rem;
}

.app-header h1 {
  background: linear-gradient(135deg, var(--accent-mint), var(--accent-teal));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  font-size: 2.2rem;
}

.app-header .subtitle {
  color: var(--text-secondary);
  font-size: 0.95rem;
  margin-top: 0.3rem;
}

/* Main content layout */
.main-content {
  display: grid;
  grid-template-columns: 1fr 350px;
  gap: 1.5rem;
  flex: 1;
}

.exercise-panel {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.mentor-panel {
  position: sticky;
  top: 1rem;
  max-height: calc(100vh - 120px);
  display: flex;
  flex-direction: column;
}

/* ============================================================
   Cards
   ============================================================ */

.card {
  background: var(--bg-card);
  border-radius: var(--border-radius);
  padding: 1.5rem;
  box-shadow: var(--shadow);
  border: 1px solid rgba(255,255,255,0.05);
}

.card-light {
  background: var(--bg-card-light);
  color: var(--text-dark);
}

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

.card-title {
  font-size: 1.1rem;
  font-weight: 600;
}

/* ============================================================
   Home Screen
   ============================================================ */

.home-screen {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 70vh;
  text-align: center;
  gap: 2rem;
}

.home-screen h1 {
  font-size: 3rem;
  margin-bottom: 0.5rem;
}

.home-question {
  font-size: 1.3rem;
  color: var(--text-secondary);
  margin-bottom: 1rem;
}

.home-options {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  width: 100%;
  max-width: 400px;
}

.home-btn {
  padding: 1rem 2rem;
  border: none;
  border-radius: var(--border-radius);
  font-size: 1.1rem;
  font-weight: 700;
  cursor: pointer;
  transition: var(--transition);
  text-transform: none;
}

.home-btn:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow);
}

.btn-oxidation {
  background: var(--accent-orange);
  color: var(--text-dark);
}

.btn-identify {
  background: var(--accent-teal);
  color: var(--text-dark);
}

.btn-balance {
  background: var(--accent-green);
  color: var(--text-dark);
}

/* ============================================================
   Progress Bar
   ============================================================ */

.progress-bar-container {
  background: rgba(255,255,255,0.1);
  border-radius: 20px;
  padding: 0.3rem;
  margin-bottom: 1rem;
}

.progress-steps {
  display: flex;
  gap: 0.25rem;
}

.progress-step {
  flex: 1;
  height: 8px;
  border-radius: 4px;
  background: rgba(255,255,255,0.1);
  transition: var(--transition);
}

.progress-step.active {
  background: var(--accent-teal);
}

.progress-step.completed {
  background: var(--accent-green);
}

.progress-label {
  text-align: center;
  font-size: 0.85rem;
  color: var(--text-secondary);
  margin-top: 0.5rem;
}

/* ============================================================
   Equation Display
   ============================================================ */

.equation-display {
  background: var(--bg-card-light);
  color: var(--text-dark);
  padding: 1.2rem 1.5rem;
  border-radius: var(--border-radius);
  font-size: 1.3rem;
  text-align: center;
  font-weight: 500;
  letter-spacing: 0.5px;
  box-shadow: var(--shadow-sm);
}

.equation-display sub {
  font-size: 0.75em;
}

.equation-display sup {
  font-size: 0.7em;
}

/* ============================================================
   Oxidation State Inputs
   ============================================================ */

.compound-group {
  display: flex;
  flex-wrap: wrap;
  gap: 2rem;
  justify-content: center;
  margin: 1.5rem 0;
}

.compound-card {
  background: var(--bg-card-light);
  border-radius: var(--border-radius);
  padding: 1.5rem;
  text-align: center;
  min-width: 140px;
  box-shadow: var(--shadow-sm);
}

.compound-formula {
  font-size: 1.8rem;
  font-weight: 600;
  color: var(--text-dark);
  margin-bottom: 1rem;
}

.ox-state-inputs {
  display: flex;
  gap: 0.5rem;
  justify-content: center;
}

.ox-input-group {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.3rem;
}

.ox-input-group label {
  font-size: 0.8rem;
  color: var(--text-muted);
  font-weight: 600;
}

.ox-input {
  width: 50px;
  height: 36px;
  text-align: center;
  border: 2px dashed var(--accent-teal);
  border-radius: var(--border-radius-sm);
  background: white;
  font-size: 1rem;
  font-weight: 700;
  color: var(--text-dark);
  outline: none;
  transition: var(--transition);
}

.ox-input:focus {
  border-color: var(--accent-purple);
  border-style: solid;
  box-shadow: 0 0 0 3px rgba(139, 92, 246, 0.2);
}

.ox-input.correct {
  border-color: var(--success-color);
  border-style: solid;
  background: #dcfce7;
}

.ox-input.incorrect {
  border-color: var(--error-color);
  border-style: solid;
  background: #fef2f2;
  animation: shake 0.5s ease-in-out;
}

/* ============================================================
   Yes/No Buttons
   ============================================================ */

.yes-no-container {
  display: flex;
  gap: 2rem;
  justify-content: center;
  margin: 2rem 0;
}

.btn-yes, .btn-no {
  padding: 1rem 3rem;
  border: none;
  border-radius: var(--border-radius);
  font-size: 1.2rem;
  font-weight: 700;
  cursor: pointer;
  transition: var(--transition);
}

.btn-yes {
  background: var(--accent-green);
  color: white;
  clip-path: polygon(50% 0%, 100% 100%, 0% 100%);
  width: 100px;
  height: 90px;
  display: flex;
  align-items: center;
  justify-content: center;
  padding-top: 30px;
}

.btn-no {
  background: var(--accent-red);
  color: white;
  clip-path: polygon(0% 0%, 100% 0%, 50% 100%);
  width: 100px;
  height: 90px;
  display: flex;
  align-items: center;
  justify-content: center;
  padding-bottom: 30px;
}

.btn-yes:hover, .btn-no:hover {
  transform: scale(1.1);
}

/* ============================================================
   Drag & Drop Areas
   ============================================================ */

.drag-drop-container {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.5rem;
  margin: 1.5rem 0;
}

.drop-zone {
  background: rgba(255,255,255,0.05);
  border: 2px dashed rgba(255,255,255,0.2);
  border-radius: var(--border-radius);
  min-height: 120px;
  padding: 1rem;
  transition: var(--transition);
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.drop-zone.oxidation {
  border-color: rgba(239, 68, 68, 0.3);
}

.drop-zone.reduction {
  border-color: rgba(34, 197, 94, 0.3);
}

.drop-zone.drag-over {
  background: rgba(255,255,255,0.1);
  border-style: solid;
}

.drop-zone-label {
  font-weight: 700;
  font-size: 0.9rem;
  padding: 0.3rem 0.8rem;
  border-radius: 20px;
  display: inline-block;
  width: fit-content;
  margin-bottom: 0.5rem;
}

.drop-zone.oxidation .drop-zone-label {
  background: var(--oxidation-color);
  color: white;
}

.drop-zone.reduction .drop-zone-label {
  background: var(--reduction-color);
  color: white;
}

.drop-zone .half-arrow {
  text-align: center;
  font-size: 1.5rem;
  color: var(--text-secondary);
  padding: 0.5rem 0;
}

.species-pool {
  display: flex;
  flex-wrap: wrap;
  gap: 0.8rem;
  justify-content: center;
  margin: 1.5rem 0;
  padding: 1rem;
  background: rgba(255,255,255,0.05);
  border-radius: var(--border-radius);
}

.species-chip {
  background: #fef08a;
  color: var(--text-dark);
  padding: 0.5rem 1rem;
  border-radius: var(--border-radius-sm);
  font-size: 1.1rem;
  font-weight: 600;
  cursor: grab;
  user-select: none;
  transition: var(--transition);
  box-shadow: var(--shadow-sm);
}

.species-chip:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow);
}

.species-chip.dragging {
  opacity: 0.5;
  cursor: grabbing;
}

.species-chip.placed {
  background: #d1d5db;
  cursor: default;
  opacity: 0.5;
}

/* Dropped items inside zones */
.dropped-species {
  background: var(--bg-card-light);
  color: var(--text-dark);
  padding: 0.4rem 0.8rem;
  border-radius: var(--border-radius-sm);
  font-size: 1rem;
  font-weight: 600;
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
}

.dropped-species .remove-btn {
  cursor: pointer;
  color: var(--accent-red);
  font-weight: 700;
  font-size: 0.9rem;
}

/* ============================================================
   Balance Inputs (Semireactions)
   ============================================================ */

.semireaction-area {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
  margin: 1.5rem 0;
}

.semireaction-box {
  background: rgba(255,255,255,0.05);
  border-radius: var(--border-radius);
  padding: 1.2rem;
  border-left: 4px solid;
}

.semireaction-box.oxidation {
  border-left-color: var(--oxidation-color);
}

.semireaction-box.reduction {
  border-left-color: var(--reduction-color);
}

.semireaction-label {
  font-weight: 700;
  font-size: 0.9rem;
  margin-bottom: 0.8rem;
  padding: 0.2rem 0.6rem;
  border-radius: 4px;
  display: inline-block;
}

.semireaction-box.oxidation .semireaction-label {
  background: var(--oxidation-color);
}

.semireaction-box.reduction .semireaction-label {
  background: var(--reduction-color);
}

.semireaction-equation {
  font-size: 1.2rem;
  padding: 0.8rem;
  background: var(--bg-card-light);
  color: var(--text-dark);
  border-radius: var(--border-radius-sm);
  text-align: center;
  margin-bottom: 0.8rem;
}

.balance-input-row {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  justify-content: center;
  flex-wrap: wrap;
}

.balance-input-row label {
  font-size: 0.95rem;
  color: var(--text-secondary);
}

.coeff-input {
  width: 60px;
  height: 40px;
  text-align: center;
  border: 2px dashed var(--accent-teal);
  border-radius: var(--border-radius-sm);
  background: rgba(255,255,255,0.1);
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text-primary);
  outline: none;
  transition: var(--transition);
}

.coeff-input:focus {
  border-color: var(--accent-purple);
  border-style: solid;
  background: rgba(255,255,255,0.15);
}

/* ============================================================
   Step instruction banner
   ============================================================ */

.step-instruction {
  background: var(--accent-teal);
  color: var(--text-dark);
  padding: 0.8rem 1.2rem;
  border-radius: var(--border-radius-sm);
  font-weight: 700;
  font-size: 0.95rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.step-instruction.warning {
  background: var(--accent-orange);
}

/* ============================================================
   Buttons
   ============================================================ */

.btn {
  padding: 0.7rem 1.5rem;
  border: none;
  border-radius: var(--border-radius-sm);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: var(--transition);
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
}

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

.btn:active {
  transform: translateY(0);
}

.btn-primary {
  background: var(--accent-teal);
  color: var(--text-dark);
}

.btn-secondary {
  background: rgba(255,255,255,0.1);
  color: var(--text-primary);
  border: 1px solid rgba(255,255,255,0.2);
}

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

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

.btn-danger {
  background: var(--error-color);
  color: white;
}

.btn-lg {
  padding: 1rem 2rem;
  font-size: 1.1rem;
}

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

.btn-group {
  display: flex;
  gap: 0.8rem;
  justify-content: center;
  margin-top: 1rem;
}

/* ============================================================
   Chat / Mentor Panel
   ============================================================ */

.mentor-card {
  background: var(--bg-card);
  border-radius: var(--border-radius);
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  height: 100%;
  border: 1px solid rgba(255,255,255,0.05);
  overflow: hidden;
}

.mentor-header {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  padding: 1rem 1.2rem;
  background: rgba(255,255,255,0.05);
  border-bottom: 1px solid rgba(255,255,255,0.1);
}

.mentor-avatar {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--accent-teal), var(--accent-green));
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.3rem;
}

.mentor-info h3 {
  font-size: 0.95rem;
}

.mentor-info .status {
  font-size: 0.75rem;
  color: var(--accent-green);
}

.chat-messages {
  flex: 1;
  overflow-y: auto;
  padding: 1rem;
  display: flex;
  flex-direction: column;
  gap: 0.8rem;
  min-height: 300px;
  max-height: 500px;
}

.chat-message {
  max-width: 85%;
  padding: 0.7rem 1rem;
  border-radius: var(--border-radius-sm);
  font-size: 0.9rem;
  line-height: 1.5;
  animation: fadeIn 0.3s ease;
}

.chat-message.mentor {
  background: rgba(255,255,255,0.08);
  align-self: flex-start;
  border-bottom-left-radius: 4px;
}

.chat-message.student {
  background: var(--accent-teal);
  color: var(--text-dark);
  align-self: flex-end;
  border-bottom-right-radius: 4px;
}

.chat-message.system {
  background: rgba(139, 92, 246, 0.2);
  color: var(--accent-mint);
  align-self: center;
  text-align: center;
  font-size: 0.85rem;
  max-width: 100%;
}

.chat-message.hint {
  background: rgba(245, 158, 11, 0.15);
  border: 1px solid rgba(245, 158, 11, 0.3);
  color: var(--accent-orange);
  align-self: flex-start;
  font-size: 0.85rem;
}

.chat-input-area {
  padding: 0.8rem;
  border-top: 1px solid rgba(255,255,255,0.1);
  display: flex;
  gap: 0.5rem;
}

.chat-input {
  flex: 1;
  padding: 0.6rem 1rem;
  border: 1px solid rgba(255,255,255,0.2);
  border-radius: 20px;
  background: rgba(255,255,255,0.05);
  color: var(--text-primary);
  font-size: 0.9rem;
  outline: none;
  transition: var(--transition);
}

.chat-input:focus {
  border-color: var(--accent-teal);
  background: rgba(255,255,255,0.08);
}

.chat-input::placeholder {
  color: var(--text-muted);
}

.chat-send-btn {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  border: none;
  background: var(--accent-teal);
  color: var(--text-dark);
  cursor: pointer;
  font-size: 1.1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: var(--transition);
}

.chat-send-btn:hover {
  background: var(--accent-green);
}

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

.typing-indicator {
  display: flex;
  gap: 4px;
  padding: 0.5rem 1rem;
  align-self: flex-start;
}

.typing-indicator span {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--text-muted);
  animation: typing 1.4s infinite ease-in-out;
}

.typing-indicator span:nth-child(2) { animation-delay: 0.2s; }
.typing-indicator span:nth-child(3) { animation-delay: 0.4s; }

/* ============================================================
   Feedback Messages
   ============================================================ */

.feedback {
  padding: 0.8rem 1.2rem;
  border-radius: var(--border-radius-sm);
  font-weight: 600;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  animation: fadeIn 0.3s ease;
}

.feedback.success {
  background: rgba(34, 197, 94, 0.15);
  border: 1px solid rgba(34, 197, 94, 0.3);
  color: var(--success-color);
}

.feedback.error {
  background: rgba(239, 68, 68, 0.15);
  border: 1px solid rgba(239, 68, 68, 0.3);
  color: var(--error-color);
}

.feedback.info {
  background: rgba(59, 130, 246, 0.15);
  border: 1px solid rgba(59, 130, 246, 0.3);
  color: var(--accent-blue);
}

/* ============================================================
   Final Result
   ============================================================ */

.final-result {
  text-align: center;
  padding: 2rem;
  animation: fadeIn 0.5s ease;
}

.final-result h2 {
  font-size: 2rem;
  margin-bottom: 1rem;
}

.final-equation-display {
  background: var(--bg-card-light);
  color: var(--text-dark);
  padding: 1.5rem 2rem;
  border-radius: var(--border-radius);
  font-size: 1.5rem;
  font-weight: 600;
  margin: 1.5rem 0;
  box-shadow: var(--shadow);
  border: 3px solid var(--accent-green);
}

.confetti-container {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
  z-index: 1000;
}

/* ============================================================
   Rules Panel (shown on "I need a clue")
   ============================================================ */

.rules-panel {
  background: var(--bg-card);
  border-radius: var(--border-radius);
  padding: 1.2rem;
  margin-top: 1rem;
  border: 1px solid rgba(245, 158, 11, 0.3);
  font-size: 0.85rem;
  line-height: 1.7;
  display: none;
}

.rules-panel.visible {
  display: block;
  animation: slideDown 0.3s ease;
}

.rules-panel h4 {
  color: var(--accent-orange);
  margin-bottom: 0.5rem;
}

.rules-panel ol, .rules-panel ul {
  padding-left: 1.5rem;
}

.rules-panel li {
  margin-bottom: 0.3rem;
  color: var(--text-secondary);
}

/* ============================================================
   Difficulty selector
   ============================================================ */

.difficulty-selector {
  display: flex;
  gap: 0.8rem;
  justify-content: center;
  margin: 1rem 0;
}

.difficulty-chip {
  padding: 0.5rem 1.2rem;
  border-radius: 20px;
  border: 2px solid rgba(255,255,255,0.2);
  background: transparent;
  color: var(--text-secondary);
  cursor: pointer;
  font-size: 0.9rem;
  font-weight: 600;
  transition: var(--transition);
}

.difficulty-chip:hover,
.difficulty-chip.active {
  border-color: var(--accent-teal);
  color: var(--accent-teal);
  background: rgba(45, 212, 191, 0.1);
}

.difficulty-chip.basic.active { border-color: var(--accent-green); color: var(--accent-green); }
.difficulty-chip.intermediate.active { border-color: var(--accent-orange); color: var(--accent-orange); }
.difficulty-chip.advanced.active { border-color: var(--accent-red); color: var(--accent-red); }

/* ============================================================
   Animations
   ============================================================ */

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

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

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-5px); }
  75% { transform: translateX(5px); }
}

@keyframes typing {
  0%, 100% { opacity: 0.3; transform: translateY(0); }
  50% { opacity: 1; transform: translateY(-4px); }
}

@keyframes pulse {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.05); }
}

.animate-success {
  animation: pulse 0.5s ease;
}

/* ============================================================
   Scrollbar
   ============================================================ */

::-webkit-scrollbar {
  width: 6px;
}

::-webkit-scrollbar-track {
  background: transparent;
}

::-webkit-scrollbar-thumb {
  background: rgba(255,255,255,0.15);
  border-radius: 3px;
}

::-webkit-scrollbar-thumb:hover {
  background: rgba(255,255,255,0.25);
}

/* ============================================================
   Responsive
   ============================================================ */

@media (max-width: 900px) {
  .main-content {
    grid-template-columns: 1fr;
  }

  .mentor-panel {
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    max-height: 60vh;
    z-index: 100;
    transform: translateY(calc(100% - 50px));
    transition: transform 0.3s ease;
    border-radius: var(--border-radius) var(--border-radius) 0 0;
  }

  .mentor-panel.expanded {
    transform: translateY(0);
  }

  .mentor-panel .mentor-header {
    cursor: pointer;
  }

  .exercise-panel {
    padding-bottom: 60px;
  }

  .drag-drop-container {
    grid-template-columns: 1fr;
  }

  .home-screen h1 {
    font-size: 2rem;
  }

  .equation-display {
    font-size: 1rem;
  }
}

@media (max-width: 600px) {
  .compound-group {
    gap: 1rem;
  }

  .compound-card {
    min-width: 100px;
    padding: 1rem;
  }

  .compound-formula {
    font-size: 1.4rem;
  }

  .btn-group {
    flex-direction: column;
  }
}

/* ============================================================
   Hidden utility
   ============================================================ */

.hidden {
  display: none !important;
}

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
}