* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --bg-primary: #0d1117;
  --bg-secondary: #161b22;
  --bg-tertiary: #21262d;
  --text-primary: #c9d1d9;
  --text-secondary: #8b949e;
  --accent: #58a6ff;
  --accent-hover: #79c0ff;
  --success: #3fb950;
  --error: #f85149;
  --warning: #d29922;
  --border: #30363d;
  --terminal-bg: #0d1117;
  --terminal-text: #c9d1d9;
  --terminal-green: #3fb950;
  --sidebar-width: 280px;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen', 'Ubuntu', 'Cantarell', sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  overflow-x: hidden;
}

/* Mode Selection Screen */
.mode-selection {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 2rem;
  background: linear-gradient(135deg, var(--bg-primary) 0%, var(--bg-secondary) 100%);
}

.mode-selection-content {
  max-width: 1000px;
  width: 100%;
}

.mode-title {
  font-size: 2.5rem;
  font-weight: 600;
  text-align: center;
  margin-bottom: 0.5rem;
  color: var(--text-primary);
}

.mode-subtitle {
  text-align: center;
  color: var(--text-secondary);
  font-size: 1.1rem;
  margin-bottom: 3rem;
}

.mode-cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 2rem;
}

.mode-card {
  background: var(--bg-secondary);
  border: 2px solid var(--border);
  border-radius: 12px;
  padding: 2rem;
  cursor: pointer;
  transition: all 0.3s;
  text-align: center;
}

.mode-card:hover {
  border-color: var(--accent);
  transform: translateY(-4px);
  box-shadow: 0 8px 24px rgba(88, 166, 255, 0.2);
}

.mode-icon {
  font-size: 4rem;
  margin-bottom: 1rem;
}

.mode-card-title {
  font-size: 1.5rem;
  font-weight: 600;
  margin-bottom: 1rem;
  color: var(--text-primary);
}

.mode-card-description {
  color: var(--text-secondary);
  margin-bottom: 1.5rem;
  line-height: 1.6;
}

.mode-features {
  list-style: none;
  text-align: left;
  margin-bottom: 1.5rem;
  color: var(--text-secondary);
}

.mode-features li {
  padding: 0.5rem 0;
  font-size: 0.95rem;
}

.mode-btn {
  width: 100%;
  padding: 0.75rem 1.5rem;
  background: var(--accent);
  color: white;
  border: none;
  border-radius: 6px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.2s;
}

.mode-btn:hover {
  background: var(--accent-hover);
}

.container {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* Header */
.header {
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border);
  padding: 1.5rem 2rem;
}

.header-content {
  max-width: 1400px;
  margin: 0 auto;
}

.back-link {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--accent);
  text-decoration: none;
  font-size: 0.9rem;
  margin-bottom: 1rem;
  transition: color 0.2s;
}

.back-link:hover {
  color: var(--accent-hover);
}

.title {
  font-size: 2rem;
  font-weight: 600;
  margin-bottom: 0.5rem;
  color: var(--text-primary);
}

.subtitle {
  color: var(--text-secondary);
  font-size: 1rem;
}

/* Main Content */
.main-content {
  display: flex;
  flex: 1;
  max-width: 1400px;
  margin: 0 auto;
  width: 100%;
  padding: 2rem;
  gap: 2rem;
}

/* Sidebar */
.sidebar {
  width: var(--sidebar-width);
  flex-shrink: 0;
  display: flex;
  flex-direction: column;
  gap: 2rem;
}

.sidebar-section {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1.5rem;
}

.sidebar-title {
  font-size: 1.1rem;
  font-weight: 600;
  margin-bottom: 1rem;
  color: var(--text-primary);
}

.commands-list {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.command-item {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.75rem;
  border-radius: 6px;
  cursor: pointer;
  transition: all 0.2s;
  border: 1px solid transparent;
}

.command-item:hover {
  background: var(--bg-tertiary);
  border-color: var(--border);
}

.command-item.learned {
  border-color: var(--success);
  background: rgba(63, 185, 80, 0.1);
}

.command-icon {
  font-size: 1.2rem;
  color: var(--text-secondary);
  width: 20px;
  text-align: center;
}

.command-item.learned .command-icon {
  color: var(--success);
}

.command-name {
  font-weight: 500;
  color: var(--text-primary);
}

.progress-info {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.btn-help {
  width: 100%;
  padding: 0.75rem;
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  color: var(--text-primary);
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.9rem;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  transition: all 0.2s;
  margin-bottom: 0.5rem;
}

.btn-help:hover {
  background: var(--bg-primary);
  border-color: var(--accent);
}

.mode-badge {
  padding: 0.5rem 1rem;
  border-radius: 6px;
  font-weight: 600;
  text-align: center;
  margin-bottom: 1rem;
}

.mode-badge-sandbox {
  background: rgba(88, 166, 255, 0.2);
  border: 1px solid var(--accent);
  color: var(--accent);
}

.mode-badge-trainer {
  background: rgba(63, 185, 80, 0.2);
  border: 1px solid var(--success);
  color: var(--success);
}

.btn-switch-mode {
  width: 100%;
  padding: 0.75rem;
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  color: var(--text-primary);
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.9rem;
  transition: all 0.2s;
}

.btn-switch-mode:hover {
  background: var(--bg-primary);
  border-color: var(--warning);
}

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

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

.stat-value {
  color: var(--accent);
  font-weight: 600;
  font-size: 1.1rem;
}

/* Content Area */
.content-area {
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

/* Command Info */
.command-info {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1.5rem;
}

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

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

.btn-reset {
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  color: var(--text-primary);
  padding: 0.5rem 1rem;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.9rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  transition: all 0.2s;
}

.btn-reset:hover {
  background: var(--bg-primary);
  border-color: var(--accent);
}

.command-description {
  color: var(--text-secondary);
  font-size: 1rem;
  margin-bottom: 1rem;
}

.command-syntax {
  background: var(--bg-tertiary);
  padding: 0.75rem;
  border-radius: 6px;
  margin-top: 1rem;
  border-left: 3px solid var(--accent);
}

.command-syntax code {
  color: var(--accent);
  font-family: 'Courier New', monospace;
  font-size: 0.9rem;
}

.command-examples {
  margin-top: 1rem;
}

.command-examples ul {
  list-style: none;
  margin-top: 0.5rem;
}

.command-examples li {
  padding: 0.25rem 0;
  color: var(--text-secondary);
}

.command-examples code {
  background: var(--bg-tertiary);
  padding: 0.25rem 0.5rem;
  border-radius: 4px;
  font-family: 'Courier New', monospace;
  font-size: 0.9rem;
  color: var(--accent);
}

/* Terminal */
.terminal-container {
  background: var(--terminal-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
}

.terminal-header {
  background: var(--bg-tertiary);
  padding: 0.75rem 1rem;
  display: flex;
  align-items: center;
  gap: 1rem;
  border-bottom: 1px solid var(--border);
}

.terminal-buttons {
  display: flex;
  gap: 0.5rem;
}

.terminal-btn {
  width: 12px;
  height: 12px;
  border-radius: 50%;
}

.terminal-btn.red {
  background: #ff5f56;
}

.terminal-btn.yellow {
  background: #ffbd2e;
}

.terminal-btn.green {
  background: #27c93f;
}

.terminal-title {
  color: var(--text-secondary);
  font-size: 0.85rem;
  font-weight: 500;
}

.terminal-body {
  padding: 1rem;
  min-height: 200px;
  max-height: 400px;
  overflow-y: auto;
  font-family: 'Courier New', 'Monaco', monospace;
  font-size: 0.9rem;
  line-height: 1.6;
}

.terminal-line {
  color: var(--terminal-text);
  margin-bottom: 0.25rem;
  white-space: pre-wrap;
  word-break: break-word;
}

.terminal-prompt {
  color: var(--terminal-green);
  font-weight: 600;
}

.terminal-cursor {
  color: var(--terminal-text);
  animation: blink 1s infinite;
}

@keyframes blink {
  0%, 50% { opacity: 1; }
  51%, 100% { opacity: 0; }
}

.terminal-input-container {
  border-top: 1px solid var(--border);
  padding: 0.75rem 1rem;
  background: var(--bg-tertiary);
}

.terminal-input {
  width: 100%;
  background: transparent;
  border: none;
  color: var(--text-primary);
  font-family: 'Courier New', 'Monaco', monospace;
  font-size: 0.9rem;
  outline: none;
}

.terminal-input::placeholder {
  color: var(--text-secondary);
}

/* Exercise Panel */
.exercise-panel {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1.5rem;
}

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

.exercise-title {
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--text-primary);
}

.exercise-number {
  color: var(--text-secondary);
  font-size: 0.9rem;
  background: var(--bg-tertiary);
  padding: 0.25rem 0.75rem;
  border-radius: 12px;
}

.exercise-description {
  color: var(--text-primary);
  font-size: 1rem;
  margin-bottom: 1rem;
}

.exercise-hint {
  display: flex;
  align-items: flex-start;
  gap: 0.75rem;
  background: rgba(88, 166, 255, 0.1);
  border: 1px solid var(--accent);
  border-radius: 6px;
  padding: 1rem;
  margin-top: 1rem;
}

.exercise-hint .icon-hint {
  font-size: 1.2rem;
  flex-shrink: 0;
}

.exercise-actions {
  display: flex;
  gap: 1rem;
  margin-top: 1rem;
}

.btn-hint,
.btn-skip {
  padding: 0.75rem 1.5rem;
  border-radius: 6px;
  border: 1px solid var(--border);
  background: var(--bg-tertiary);
  color: var(--text-primary);
  cursor: pointer;
  font-size: 0.9rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  transition: all 0.2s;
}

.btn-hint:hover {
  background: rgba(88, 166, 255, 0.2);
  border-color: var(--accent);
}

.btn-skip:hover {
  background: var(--bg-primary);
  border-color: var(--warning);
}

/* File System View */
.filesystem-view {
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1.5rem;
}

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

.filesystem-header h3 {
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--text-primary);
}

.current-path {
  color: var(--accent);
  font-family: 'Courier New', monospace;
  font-size: 0.9rem;
  background: var(--bg-tertiary);
  padding: 0.25rem 0.75rem;
  border-radius: 4px;
}

.filesystem-content {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(120px, 1fr));
  gap: 1rem;
}

.fs-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.5rem;
  padding: 1rem;
  border-radius: 6px;
  border: 1px solid var(--border);
  background: var(--bg-tertiary);
  transition: all 0.2s;
  cursor: default;
}

.fs-item:hover {
  border-color: var(--accent);
  background: var(--bg-secondary);
}

.fs-icon {
  font-size: 2rem;
}

.fs-name {
  font-size: 0.85rem;
  color: var(--text-primary);
  text-align: center;
  word-break: break-word;
}

/* Scrollbar */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

::-webkit-scrollbar-track {
  background: var(--bg-primary);
}

::-webkit-scrollbar-thumb {
  background: var(--border);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--text-secondary);
}

/* Help Modal */
.help-modal {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  z-index: 1000;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 2rem;
}

.help-modal-backdrop {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(0, 0, 0, 0.7);
  backdrop-filter: blur(4px);
}

.help-modal-content {
  position: relative;
  background: var(--bg-secondary);
  border: 1px solid var(--border);
  border-radius: 12px;
  max-width: 800px;
  max-height: 80vh;
  width: 100%;
  display: flex;
  flex-direction: column;
  z-index: 1001;
  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.5);
}

.help-modal-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1.5rem;
  border-bottom: 1px solid var(--border);
}

.help-modal-header h3 {
  font-size: 1.5rem;
  font-weight: 600;
  color: var(--text-primary);
}

.help-modal-close {
  background: none;
  border: none;
  color: var(--text-secondary);
  font-size: 2rem;
  cursor: pointer;
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 4px;
  transition: all 0.2s;
}

.help-modal-close:hover {
  background: var(--bg-tertiary);
  color: var(--text-primary);
}

.help-modal-body {
  padding: 1.5rem;
  overflow-y: auto;
  flex: 1;
}

.help-commands-list {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.help-command-item {
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1rem;
  cursor: pointer;
  transition: all 0.2s;
}

.help-command-item:hover {
  border-color: var(--accent);
  background: var(--bg-secondary);
}

.help-command-item h4 {
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--accent);
  margin-bottom: 0.5rem;
}

.help-command-item p {
  color: var(--text-secondary);
  margin-bottom: 0.5rem;
}

.help-command-item code {
  background: var(--bg-primary);
  padding: 0.25rem 0.5rem;
  border-radius: 4px;
  font-family: 'Courier New', monospace;
  color: var(--accent);
}

.help-examples {
  margin-top: 0.75rem;
}

.help-examples strong {
  color: var(--text-primary);
  font-size: 0.9rem;
}

.help-examples ul {
  list-style: none;
  margin-top: 0.5rem;
}

.help-examples li {
  padding: 0.25rem 0;
  color: var(--text-secondary);
}

.help-command-detail {
  color: var(--text-primary);
}

.help-command-detail h3 {
  font-size: 1.8rem;
  color: var(--accent);
  margin-bottom: 1rem;
}

.help-description {
  color: var(--text-secondary);
  font-size: 1.1rem;
  margin-bottom: 1.5rem;
}

.help-syntax {
  background: var(--bg-tertiary);
  padding: 1rem;
  border-radius: 6px;
  margin-bottom: 1.5rem;
  border-left: 3px solid var(--accent);
}

.help-syntax strong {
  display: block;
  margin-bottom: 0.5rem;
  color: var(--text-primary);
}

.help-syntax code {
  font-family: 'Courier New', monospace;
  font-size: 1.1rem;
  color: var(--accent);
}

.help-detailed {
  margin-bottom: 1.5rem;
}

.help-detailed strong {
  display: block;
  margin-bottom: 0.5rem;
  color: var(--text-primary);
}

.help-detailed p {
  color: var(--text-secondary);
  line-height: 1.6;
}

/* Responsive */
@media (max-width: 1024px) {
  .main-content {
    flex-direction: column;
  }
  
  .sidebar {
    width: 100%;
  }
  
  .filesystem-content {
    grid-template-columns: repeat(auto-fill, minmax(100px, 1fr));
  }
}

@media (max-width: 768px) {
  .mode-selection {
    padding: 1rem;
  }
  
  .mode-title {
    font-size: 2rem;
  }
  
  .mode-cards {
    grid-template-columns: 1fr;
  }
  
  .header {
    padding: 1rem;
  }
  
  .title {
    font-size: 1.5rem;
  }
  
  .main-content {
    padding: 1rem;
    gap: 1rem;
  }
  
  .command-header {
    flex-direction: column;
    align-items: flex-start;
    gap: 1rem;
  }
  
  .exercise-actions {
    flex-direction: column;
  }
  
  .btn-hint,
  .btn-skip {
    width: 100%;
    justify-content: center;
  }
  
  .help-modal {
    padding: 1rem;
  }
  
  .help-modal-content {
    max-height: 90vh;
  }
}