color: var(--text-secondary);
  margin-top: var(--spacing-sm);
}

.header-description {
  color: var(--text-secondary);
  font-size: 1.1rem;
  margin-bottom: var(--spacing-xl);
}

/* Tab Navigation */
.tab-navigation {
  display: flex;
  justify-content: center;
  gap: var(--spacing-md);
  margin: var(--spacing-xl) 0;
  flex-wrap: wrap;
}

.tab-btn {
  background: var(--surface-bg);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: var(--spacing-md) var(--spacing-xl);
  color: var(--text-secondary);
  cursor: pointer;
  font-weight: 500;
  transition: all 0.3s ease;
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  font-size: 1rem;
  font-family: var(--font-primary);
}

.tab-btn:hover {
  background: var(--border-color);
  color: var(--text-primary);
  transform: translateY(-2px);
  box-shadow: var(--panel-shadow);
}

.tab-btn.active {
  background: linear-gradient(135deg, var(--quantum-blue), var(--velocity-blue));
  border-color: var(--quantum-blue);
  color: white;
  box-shadow: var(--glow-shadow);
}

/* Tab Content */
.tab-content {
  display: none;
}

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

/* Progress Bar */
.progress-container {
  max-width: 600px;
  margin: 0 auto;
}

.progress-label {
  display: flex;
  justify-content: space-between;
  margin-bottom: var(--spacing-sm);
  font-family: var(--font-mono);
  font-size: 0.9rem;
}

.step-count {
  color: var(--text-muted);
}

.progress-bar {
  height: 8px;
  background: var(--surface-bg);
  border-radius: 4px;
  position: relative;
  overflow: hidden;
  border: 1px solid var(--border-color);
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--quantum-blue), var(--quantum-cyan));
  border-radius: 4px;
  transition: width 0.6s cubic-bezier(0.4, 0, 0.2, 1);
  position: relative;
}

.progress-glow {
  position: absolute;
  top: 0;
  left: 0;
  height: 100%;
  width: 100%;
  background: linear-gradient(90deg,
    transparent 0%,
    rgba(0, 212, 255, 0.3) 50%,
    transparent 100%);
  animation: progress-shimmer 2s ease-in-out infinite;
}

@keyframes progress-shimmer {
  0% { transform: translateX(-100%); }
  100% { transform: translateX(100%); }
}

/* Main Grid Layout */
.main-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  grid-template-rows: auto auto;
  gap: var(--spacing-xl);
  flex: 1;
}

.animation-panel {
  grid-column: 1;
  grid-row: 1;
}

.graph-section {
  grid-column: 1;
  grid-row: 2;
  min-height: 400px;
}

.learning-panel {
  grid-column: 2;
  grid-row: 1 / 3;
}

/* Practice Section Styles */
.practice-section {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--spacing-xl);
  margin-top: var(--spacing-xl);
}

.problem-list {
  background: var(--panel-bg);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-color);
  box-shadow: var(--panel-shadow);
  padding: var(--spacing-lg);
  max-height: 80vh;
  overflow-y: auto;
}

.problem-item {
  background: var(--surface-bg);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: var(--spacing-md);
  margin-bottom: var(--spacing-md);
  cursor: pointer;
  transition: all 0.3s ease;
  position: relative;
}

.problem-item:hover {
  background: var(--border-color);
  transform: translateY(-2px);
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
}

.problem-item.active {
  border-color: var(--quantum-blue);
  background: rgba(0, 212, 255, 0.1);
  box-shadow: var(--glow-shadow);
}

.problem-title {
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: var(--spacing-xs);
  font-size: 0.95rem;
  padding-right: 60px; /* Space for difficulty badge */
}

.problem-preview {
  color: var(--text-muted);
  font-size: 0.85rem;
  line-height: 1.4;
}

.problem-difficulty {
  position: absolute;
  top: var(--spacing-sm);
  right: var(--spacing-sm);
  padding: 2px 8px;
  border-radius: 12px;
  font-size: 0.75rem;
  font-weight: 500;
}

.difficulty-easy { 
  background: rgba(16, 185, 129, 0.2); 
  color: var(--potential-green);
  border: 1px solid rgba(16, 185, 129, 0.3);
}

.difficulty-medium { 
  background: rgba(245, 158, 11, 0.2); 
  color: var(--kinetic-orange);
  border: 1px solid rgba(245, 158, 11, 0.3);
}

.difficulty-hard { 
  background: rgba(239, 68, 68, 0.2); 
  color: var(--energy-red);
  border: 1px solid rgba(239, 68, 68, 0.3);
}

.problem-solution {
  background: var(--panel-bg);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-color);
  box-shadow: var(--panel-shadow);
  padding: var(--spacing-lg);
  max-height: 80vh;
  overflow-y: auto;
}

.solution-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: var(--spacing-lg);
  padding-bottom: var(--spacing-md);
  border-bottom: 1px solid var(--border-color);
}

.solution-title {
  font-size: 1.3rem;
  font-weight: 600;
  color: var(--text-primary);
}

.solution-content {
  color: var(--text-secondary);
  line-height: 1.7;
}

.solution-step {
  background: var(--surface-bg);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  padding: var(--spacing-md);
  margin-bottom: var(--spacing-md);
}

.step-title {
  font-weight: 600;
  color: var(--quantum-cyan);
  margin-bottom: var(--spacing-sm);
  font-size: 0.95rem;
}

.step-content {
  color: var(--text-secondary);
  margin-bottom: var(--spacing-sm);
}

.formula {
  background: var(--primary-bg);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: var(--spacing-sm) var(--spacing-md);
  font-family: var(--font-mono);
  color: var(--quantum-cyan);
  margin: var(--spacing-sm) 0;
  font-size: 0.9rem;
}

.answer-box {
  background: linear-gradient(135deg, rgba(16, 185, 129, 0.1), rgba(6, 255, 165, 0.1));
  border: 2px solid var(--potential-green);
  border-radius: var(--radius-md);
  padding: var(--spacing-md);
  margin-top: var(--spacing-md);
  text-align: center;
}

.answer-label {
  color: var(--potential-green);
  font-weight: 600;
  margin-bottom: var(--spacing-xs);
}

.answer-value {
  font-family: var(--font-mono);
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--text-primary);
}

/* Interactive Practice Widget */
.practice-widget {
  background: var(--surface-bg);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: var(--spacing-lg);
  margin-top: var(--spacing-lg);
}

.widget-header {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  margin-bottom: var(--spacing-md);
}

.widget-title {
  font-weight: 600;
  color: var(--text-primary);
}

.input-group {
  display: flex;
  gap: var(--spacing-sm);
  margin-bottom: var(--spacing-md);
}

.practice-input {
  flex: 1;
  background: var(--primary-bg);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: var(--spacing-sm) var(--spacing-md);
  color: var(--text-primary);
  font-family: var(--font-mono);
  font-size: 1rem;
  transition: all 0.3s ease;
}

.practice-input:focus {
  outline: none;
  border-color: var(--quantum-blue);
  box-shadow: 0 0 0 3px rgba(0, 212, 255, 0.1);
}

.check-btn {
  background: linear-gradient(135deg, var(--quantum-blue), var(--velocity-blue));
  border: none;
  border-radius: var(--radius-sm);
  padding: var(--spacing-sm) var(--spacing-lg);
  color: white;
  cursor: pointer;
  font-weight: 500;
  transition: all 0.3s ease;
  white-space: nowrap;
}

.check-btn:hover {
  background: linear-gradient(135deg, var(--velocity-blue), var(--quantum-blue));
  box-shadow: var(--glow-shadow);
  transform: translateY(-1px);
}

.feedback {
  padding: var(--spacing-md);
  border-radius: var(--radius-sm);
  margin-top: var(--spacing-md);
  display: none;
  align-items: center;
  gap: var(--spacing-sm);
  font-weight: 500;
}

.feedback.show {
  display: flex;
}

.feedback.correct {
  background: rgba(16, 185, 129, 0.1);
  border: 1px solid var(--potential-green);
  color: var(--potential-green);
  display: flex;
}

.feedback.incorrect {
  background: rgba(239, 68, 68, 0.1);
  border: 1px solid var(--energy-red);
  color: var(--energy-red);
  display: flex;
}

/* Panel Styles */
.panel {
  background: var(--panel-bg);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-color);
  box-shadow: var(--panel-shadow);
  padding: var(--spacing-lg);
  position: relative;
  overflow: hidden;
}

.panel::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  border-radius: var(--radius-lg);
  padding: 1px;
  background: linear-gradient(135deg,
    var(--quantum-blue) 0%,
    transparent 30%,
    transparent 70%,
    var(--quantum-purple) 100%);
  mask: linear-gradient(#fff 0 0) content-box, linear-gradient(#fff 0 0);
  mask-composite: subtract;
  opacity: 0.6;
}

.panel:hover::before {
  opacity: 1;
  animation: border-glow 2s ease-in-out infinite alternate;
}

@keyframes border-glow {
  from { filter: brightness(1); }
  to { filter: brightness(1.2); }
}

.panel-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: var(--spacing-lg);
}

.panel-title {
  font-size: 1.5rem;
  font-weight: 600;
  color: var(--text-primary);
}

.panel-controls {
  display: flex;
  gap: var(--spacing-sm);
}

/* Control Buttons */
.control-btn {
  background: var(--surface-bg);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: var(--spacing-sm);
  color: var(--text-secondary);
  cursor: pointer;
  transition: all 0.3s ease;
  display: flex;
  align-items: center;
  justify-content: center;
}

.control-btn:hover {
  background: var(--border-color);
  color: var(--text-primary);
  transform: translateY(-1px);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
}

.control-btn.primary {
  background: linear-gradient(135deg, var(--quantum-blue), var(--velocity-blue));
  border-color: var(--quantum-blue);
  color: white;
}

.control-btn.primary:hover {
  background: linear-gradient(135deg, var(--velocity-blue), var(--quantum-blue));
  box-shadow: var(--glow-shadow);
}

/* Physics Canvas */
.physics-canvas {
  background: linear-gradient(180deg,
    rgba(6, 182, 212, 0.1) 0%,
    rgba(16, 185, 129, 0.1) 100%);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  position: relative;
  height: 400px;
  overflow: hidden;
}

.height-markers {
  position: absolute;
  left: 0;
  top: 0;
  height: 100%;
  width: 100%;
  pointer-events: none;
}

.height-marker {
  position: absolute;
  left: 0;
  width: 100%;
  height: 1px;
  background: linear-gradient(90deg,
    var(--border-color) 0%,
    transparent 20%,
    transparent 80%,
    var(--border-color) 100%);
  display: flex;
  align-items: center;
}

.height-marker[data-height="0"] { bottom: 20px; }
.height-marker[data-height="20"] { bottom: 100px; }
.height-marker[data-height="40"] { bottom: 180px; }
.height-marker[data-height="60"] { bottom: 260px; }
.height-marker[data-height="80"] { bottom: 340px; }

.height-marker span {
  background: var(--surface-bg);
  color: var(--text-muted);
  padding: var(--spacing-xs) var(--spacing-sm);
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: 0.75rem;
  margin-left: var(--spacing-sm);
  border: 1px solid var(--border-color);
}

/* Ball Styles */
.ball {
  position: absolute;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  left: 50%;
  transform: translateX(-50%);
  transition: all 0.1s ease-out;
  border: 2px solid rgba(255, 255, 255, 0.3);
  box-shadow:
    0 0 20px rgba(59, 130, 246, 0.5),
    inset 0 0 20px rgba(255, 255, 255, 0.1);
}

/* Ball States */
.ball.ready {
  background: linear-gradient(135deg, var(--neutral-gray), #94a3b8);
  top: 60px;
}

.ball.falling {
  background: linear-gradient(135deg, var(--energy-red), #dc2626);
  box-shadow:
    0 0 30px rgba(239, 68, 68, 0.6),
    inset 0 0 20px rgba(255, 255, 255, 0.1);
}

.ball.rising {
  background: linear-gradient(135deg, var(--velocity-blue), #1d4ed8);
  box-shadow:
    0 0 30px rgba(59, 130, 246, 0.6),
    inset 0 0 20px rgba(255, 255, 255, 0.1);
}

.ball.bouncing {
  background: linear-gradient(135deg, var(--potential-green), #059669);
  box-shadow:
    0 0 30px rgba(16, 185, 129, 0.6),
    inset 0 0 20px rgba(255, 255, 255, 0.1);
}

/* Ground */
.ground {
  position: absolute;
  bottom: 0;
  left: 0;
  width: 100%;
  height: 20px;
  background: linear-gradient(180deg, #92400e, #78350f);
  border-top: 2px solid var(--kinetic-orange);
  box-shadow: inset 0 2px 10px rgba(0, 0, 0, 0.3);
}

/* Physics Display */
.physics-display {
  position: absolute;
  top: var(--spacing-md);
  right: var(--spacing-md);
  background: rgba(15, 23, 42, 0.9);
  backdrop-filter: blur(10px);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  padding: var(--spacing-md);
  display: flex;
  flex-direction: column;
  gap: var(--spacing-sm);
  min-width: 180px;
}

.physics-metric {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: var(--spacing-md);
}

.metric-label {
  color: var(--text-muted);
  font-size: 0.85rem;
  font-weight: 500;
}

.metric-value {
  color: var(--quantum-cyan);
  font-family: var(--font-mono);
  font-weight: 600;
  font-size: 0.9rem;
}

/* Speed-Time Graph Section */
.graph-section {
  background: var(--panel-bg);
  border-radius: var(--radius-lg);
  border: 2px solid var(--quantum-blue);
  box-shadow: var(--panel-shadow), 0 0 20px rgba(0, 212, 255, 0.2);
  padding: var(--spacing-xl);
  position: relative;
  overflow: hidden;
  display: block !important; /* Force visibility */
  margin-top: var(--spacing-lg);
}

.graph-section::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg,
    var(--quantum-blue) 0%,
    var(--quantum-purple) 50%,
    var(--quantum-cyan) 100%);
  animation: pulse-glow 2s ease-in-out infinite alternate;
}

.speed-graph-container {
  width: 100%;
  background: var(--surface-bg);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  padding: var(--spacing-lg);
  position: relative;
}

#speed-canvas {
  width: 100%;
  height: 300px;
  border-radius: var(--radius-sm);
  background: rgba(0, 0, 0, 0.4);
  border: 1px solid var(--border-color);
  display: block;
}

.graph-info {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: var(--spacing-md);
  flex-wrap: wrap;
  gap: var(--spacing-md);
}

.graph-legend {
  display: flex;
  gap: var(--spacing-lg);
  align-items: center;
}

.legend-item {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  font-size: 0.9rem;
  color: var(--text-secondary);
}

.legend-color {
  width: 16px;
  height: 3px;
  border-radius: 2px;
  display: block;
}

.graph-stats {
  display: flex;
  gap: var(--spacing-lg);
  font-size: 0.9rem;
  color: var(--text-muted);
}

.graph-stats strong {
  color: var(--quantum-cyan);
  font-family: var(--font-mono);
}

/* Learning Panel Sections */
.concept-section,
.formula-section,
.interactive-section {
  margin-bottom: var(--spacing-lg);
  padding: var(--spacing-md);
  background: var(--surface-bg);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
}

.section-header {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  margin-bottom: var(--spacing-sm);
}

.section-icon {
  font-size: 1.2rem;
}

.section-header h3 {
  color: var(--text-primary);
  font-weight: 600;
}

.concept-content p {
  color: var(--text-secondary);
  line-height: 1.7;
}

/* Formula Display */
.formula-display {
  background: var(--primary-bg);
  border-radius: var(--radius-sm);
  padding: var(--spacing-md);
  border: 1px solid var(--border-color);
}

.formula-equation {
  font-family: var(--font-mono);
  font-size: 1.1rem;
  color: var(--quantum-cyan);
  font-weight: 600;
  margin-bottom: var(--spacing-sm);
}

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

/* Interactive Elements */
.challenge-instruction {
  color: var(--text-secondary);
  margin-bottom: var(--spacing-md);
  font-weight: 500;
}

.input-container {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
}

.input-label {
  color: var(--text-primary);
  font-weight: 500;
  font-size: 0.9rem;
}

.physics-input {
  flex: 1;
  background: var(--primary-bg);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: var(--spacing-md);
  color: var(--text-primary);
  font-family: var(--font-mono);
  font-size: 1rem;
  transition: all 0.3s ease;
}

.physics-input:focus {
  outline: none;
  border-color: var(--quantum-blue);
  box-shadow: 0 0 0 3px rgba(0, 212, 255, 0.1);
}

.hint-btn {
  background: linear-gradient(135deg, var(--kinetic-orange), #d97706);
  border: none;
  border-radius: var(--radius-sm);
  padding: var(--spacing-sm) var(--spacing-md);
  color: white;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: var(--spacing-xs);
  font-weight: 500;
  transition: all 0.3s ease;
}

.hint-btn:hover {
  background: linear-gradient(135deg, #d97706, var(--kinetic-orange));
  transform: translateY(-1px);
  box-shadow: 0 4px 15px rgba(245, 158, 11, 0.3);
}

.hint-btn.active {
  background: linear-gradient(135deg, #92400e, #78350f);
}

/* Hint Display */
.hint-display {
  background: rgba(245, 158, 11, 0.1);
  border: 1px solid rgba(245, 158, 11, 0.3);
  border-radius: var(--radius-sm);
  padding: var(--spacing-md);
  display: none;
}

.hint-display.show {
  display: block;
  animation: fade-in 0.3s ease;
}

.hint-content {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  color: var(--kinetic-orange);
  font-size: 0.9rem;
}

/* Feedback Display */
.feedback-display {
  padding: var(--spacing-md);
  border-radius: var(--radius-sm);
  display: none;
  align-items: center;
  gap: var(--spacing-sm);
  font-weight: 500;
  animation: fade-in 0.3s ease;
}

.feedback-display.show {
  display: flex;
}

.feedback-display.correct {
  background: rgba(16, 185, 129, 0.1);
  border: 1px solid rgba(16, 185, 129, 0.3);
  color: var(--potential-green);
}

.feedback-display.incorrect {
  background: rgba(239, 68, 68, 0.1);
  border: 1px solid rgba(239, 68, 68, 0.3);
  color: var(--energy-red);
}

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

/* Navigation */
.navigation {
  display: flex;
  justify-content: space-between;
  margin-top: var(--spacing-xl);
  padding-top: var(--spacing-lg);
  border-top: 1px solid var(--border-color);
}

.nav-btn {
  background: var(--surface-bg);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: var(--spacing-md) var(--spacing-lg);
  color: var(--text-secondary);
  cursor: pointer;
  font-weight: 500;
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  transition: all 0.3s ease;
  font-family: var(--font-primary);
  font-size: 0.95rem;
}

.nav-btn:hover:not(:disabled) {
  background: var(--border-color);
  color: var(--text-primary);
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
}

.nav-btn.primary {
  background: linear-gradient(135deg, var(--quantum-blue), var(--velocity-blue));
  border-color: var(--quantum-blue);
  color: white;
}

.nav-btn.primary:hover:not(:disabled) {
  background: linear-gradient(135deg, var(--velocity-blue), var(--quantum-blue));
  box-shadow: var(--glow-shadow);
}

.nav-btn.secondary {
  background: var(--surface-bg);
}

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

/* Footer */
.footer {
  margin-top: auto;
  padding: var(--spacing-lg);
  background: var(--surface-bg);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
}

.footer-content {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: var(--spacing-md);
}

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

.highlight {
  color: var(--quantum-cyan);
  font-weight: 600;
}

.footer-stats {
  display: flex;
  gap: var(--spacing-lg);
}

.stat {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--spacing-xs);
}

.stat-value {
  font-family: var(--font-mono);
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--quantum-cyan);
}

.stat-label {
  font-size: 0.75rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

/* Responsive Design */
@media (max-width: 1200px) {
  .main-grid,
  .practice-section {
    grid-template-columns: 1fr;
    grid-template-rows: auto auto auto;
    gap: var(--spacing-lg);
  }
  
  .animation-panel {
    grid-column: 1;
    grid-row: 1;
  }
  
  .graph-section {
    grid-column: 1;
    grid-row: 2;
  }
  
  .learning-panel {
    grid-column: 1;
    grid-row: 3;
  }
}

@media (max-width: 768px) {
  .app-container {
    padding: var(--spacing-md);
    gap: var(--spacing-lg);
  }

  .main-title {
    font-size: 2rem;
    flex-direction: column;
    gap: var(--spacing-sm);
  }

  .tab-navigation {
    flex-direction: column;
    align-items: center;
  }
  
  .tab-btn {
    width: 100%;
    max-width: 300px;
    justify-content: center;
  }

  .panel {
    padding: var(--spacing-lg);
  }

  .panel-header {
    flex-direction: column;
    gap: var(--spacing-md);
    align-items: flex-start;
  }

  .physics-canvas {
    height: 400px;
  }

  .physics-display {
    position: static;
    margin-top: var(--spacing-md);
    background: var(--surface-bg);
  }

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

  .navigation {
    flex-direction: column;
    gap: var(--spacing-md);
  }

  .nav-btn {
    justify-content: center;
  }

  .footer-content {
    flex-direction: column;
    text-align: center;
  }

  .practice-section {
    grid-template-columns: 1fr;
    gap: var(--spacing-lg);
  }

  .problem-list,
  .problem-solution {
    max-height: 60vh;
  }
}

@media (max-width: 480px) {
  .main-title {
    font-size: 1.75rem;
  }

  .physics-canvas {
    height: 350px;
  }

  .ball {
    width: 30px;
    height: 30px;
  }

  .height-marker span {
    font-size: 0.7rem;
    padding: 2px 6px;
  }

  .section-header {
    flex-direction: column;
    align-items: flex-start;
    gap: var(--spacing-xs);
  }

  .problem-title {
    font-size: 0.9rem;
    padding-right: 50px;
  }

  .problem-preview {
    font-size: 0.8rem;
  }

  .solution-title {
    font-size: 1.1rem;
  }
}

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

.visible {
  display: block !important;
}

.glow {
  box-shadow: var(--glow-shadow);
}

.text-center {
  text-align: center;
}

.mb-lg {
  margin-bottom: var(--spacing-lg);
}

.mt-lg {
  margin-top: var(--spacing-lg);
}

/* Animation Performance Optimizations */
.ball,
.progress-fill,
.control-btn,
.nav-btn,
.tab-btn,
.problem-item {
  will-change: transform;
}

/* Print Styles */
@media print {
  body::before,
  .panel::before,
  .header::before {
    display: none;
  }

  .app-container {
    background: white;
    color: black;
  }

  .panel {
    border: 1px solid #ccc;
    box-shadow: none;
  }

  .tab-navigation,
  .footer {
    display: none;
  }
}

/* High Contrast Mode Support */
@media (prefers-contrast: high) {
  :root {
    --border-color: #fff;
    --text-secondary: #fff;
    --text-muted: #ccc;
  }
}

/* Reduced Motion Support */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }

  .ball {
    transition: none;
  }
}

/* Custom Scrollbars */
.problem-list::-webkit-scrollbar,
.problem-solution::-webkit-scrollbar {
  width: 8px;
}

.problem-list::-webkit-scrollbar-track,
.problem-solution::-webkit-scrollbar-track {
  background: var(--surface-bg);
  border-radius: var(--radius-sm);
}

.problem-list::-webkit-scrollbar-thumb,
.problem-solution::-webkit-scrollbar-thumb {
  background: var(--border-color);
  border-radius: var(--radius-sm);
}

.problem-list::-webkit-scrollbar-thumb:hover,
.problem-solution::-webkit-scrollbar-thumb:hover {
  background: var(--quantum-blue);
}/* Physics Tutorial - Dark Theme Styles with NEET Practice */

:root {
  /* Dark Physics Color Palette */
  --primary-bg: #0a0a0f;
  --secondary-bg: #1a1a2e;
  --panel-bg: #16213e;
  --surface-bg: #0f172a;
  --border-color: #334155;

  /* Quantum Glow Colors */
  --quantum-blue: #00d4ff;
  --quantum-purple: #8b5cf6;
  --quantum-cyan: #06ffa5;
  --quantum-pink: #ff006e;
  --quantum-orange: #ff8500;

  /* Physics Theme Colors */
  --energy-red: #ef4444;
  --velocity-blue: #3b82f6;
  --potential-green: #10b981;
  --kinetic-orange: #f59e0b;
  --neutral-gray: #6b7280;

  /* Text Colors */
  --text-primary: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-muted: #64748b;
  --text-accent: var(--quantum-cyan);

  /* Shadows & Glows */
  --glow-shadow: 0 0 20px rgba(0, 212, 255, 0.3);
  --panel-shadow: 0 8px 32px rgba(0, 0, 0, 0.4);
  --inner-shadow: inset 0 2px 4px rgba(0, 0, 0, 0.2);

  /* Fonts */
  --font-primary: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;

  /* Spacing */
  --spacing-xs: 0.25rem;
  --spacing-sm: 0.5rem;
  --spacing-md: 1rem;
  --spacing-lg: 1.5rem;
  --spacing-xl: 2rem;
  --spacing-2xl: 3rem;

  /* Border Radius */
  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-xl: 24px;
}

/* Reset and Base Styles */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: var(--font-primary);
  background: linear-gradient(135deg, var(--primary-bg) 0%, var(--secondary-bg) 100%);
  color: var(--text-primary);
  min-height: 100vh;
  overflow-x: hidden;
  line-height: 1.6;
}

/* Quantum Background Animation */
body::before {
  content: '';
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background:
    radial-gradient(circle at 20% 80%, rgba(0, 212, 255, 0.1) 0%, transparent 50%),
    radial-gradient(circle at 80% 20%, rgba(139, 92, 246, 0.1) 0%, transparent 50%),
    radial-gradient(circle at 40% 40%, rgba(6, 255, 165, 0.05) 0%, transparent 50%);
  z-index: -1;
  animation: quantum-drift 20s ease-in-out infinite;
}

@keyframes quantum-drift {
  0%, 100% { transform: scale(1) rotate(0deg); }
  50% { transform: scale(1.1) rotate(0.5deg); }
}

/* App Container */
.app-container {
  max-width: 1400px;
  margin: 0 auto;
  padding: var(--spacing-lg);
  display: flex;
  flex-direction: column;
  gap: var(--spacing-xl);
  min-height: 100vh;
}

/* Header Styles */
.header {
  text-align: center;
  padding: var(--spacing-xl);
  background: linear-gradient(135deg, var(--panel-bg) 0%, var(--surface-bg) 100%);
  border-radius: var(--radius-xl);
  border: 1px solid var(--border-color);
  box-shadow: var(--panel-shadow);
  position: relative;
  overflow: hidden;
}

.header::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: linear-gradient(90deg,
    var(--quantum-blue) 0%,
    var(--quantum-purple) 50%,
    var(--quantum-cyan) 100%);
  animation: pulse-glow 2s ease-in-out infinite alternate;
}

@keyframes pulse-glow {
  from { opacity: 0.5; }
  to { opacity: 1; }
}

.main-title {
  font-size: 2.5rem;
  font-weight: 700;
  margin-bottom: var(--spacing-sm);
  background: linear-gradient(135deg, var(--quantum-blue), var(--quantum-purple));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--spacing-md);
  flex-wrap: wrap;
}

.title-icon {
  font-size: 2rem;
  animation: spin-slow 10s linear infinite;
}

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

.subtitle {
  display: block;
  font-size: 1.2rem;
  font-weight: 400;
  color: var(--text-secondary