:root {
  /* Light theme colors */
  --primary-color: #6d5dfc;
  --primary-light: #8677f9;
  --primary-dark: #5346e0;
  --secondary-color: #ff7d3b;
  --accent-color: #2cc990;
  
  --bg-color: #f5f9ff;
  --bg-panel: #ffffff;
  --bg-secondary: #f0f5ff;
  
  --text-color: #2e3440;
  --text-secondary: #4c566a;
  --text-tertiary: #7b8a9b;
  
  --border-color: #e4e9f2;
  --shadow-color: rgba(149, 157, 165, 0.1);
  
  /* Sizes and spacing */
  --border-radius-sm: 4px;
  --border-radius-md: 8px;
  --border-radius-lg: 16px;
  
  --spacing-xs: 4px;
  --spacing-sm: 8px;
  --spacing-md: 16px;
  --spacing-lg: 24px;
  --spacing-xl: 32px;
  
  /* Typography */
  --font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
  --font-size-xs: 0.75rem;
  --font-size-sm: 0.875rem;
  --font-size-md: 1rem;
  --font-size-lg: 1.25rem;
  --font-size-xl: 1.5rem;
  --font-size-xxl: 2rem;
  
  /* Transitions */
  --transition-fast: 0.15s ease;
  --transition-normal: 0.3s ease;
  --transition-slow: 0.5s ease;
  
  /* Shadows */
  --shadow-sm: 0 2px 4px var(--shadow-color);
  --shadow-md: 0 4px 8px var(--shadow-color);
  --shadow-lg: 0 8px 16px var(--shadow-color);
  
  /* Z-indices */
  --z-index-modal: 1000;
  --z-index-overlay: 900;
  --z-index-dropdown: 800;
  --z-index-header: 700;
}

/* Dark theme colors */
[data-theme="dark"] {
  --primary-color: #8677f9;
  --primary-light: #a599fa;
  --primary-dark: #6d5dfc;
  --secondary-color: #ff9d6b;
  --accent-color: #3ddfa9;
  
  --bg-color: #1a1b26;
  --bg-panel: #24283b;
  --bg-secondary: #2c3049;
  
  --text-color: #d8dee9;
  --text-secondary: #a9b1d6;
  --text-tertiary: #7982a9;
  
  --border-color: #414868;
  --shadow-color: rgba(0, 0, 0, 0.3);
}

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

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

body {
  font-family: var(--font-family);
  background-color: var(--bg-color);
  color: var(--text-color);
  line-height: 1.6;
  transition: background-color var(--transition-normal), color var(--transition-normal);
  min-height: 100vh;
}

.app-container {
  max-width: 1200px;
  margin: 0 auto;
  padding: var(--spacing-md);
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  font-weight: 600;
  line-height: 1.3;
  margin-bottom: var(--spacing-md);
  color: var(--text-color);
}

h1 {
  font-size: var(--font-size-xxl);
}

h2 {
  font-size: var(--font-size-xl);
}

h3 {
  font-size: var(--font-size-lg);
}

p {
  margin-bottom: var(--spacing-md);
}

a {
  color: var(--primary-color);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--primary-light);
}

/* Header */
header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: var(--spacing-md) 0;
  margin-bottom: var(--spacing-lg);
}

.logo {
  display: flex;
  align-items: center;
  gap: var(--spacing-md);
}

.logo img {
  height: 40px;
  width: auto;
}

.theme-toggle button {
  background: none;
  border: none;
  cursor: pointer;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background-color var(--transition-fast);
}

.theme-toggle button:hover {
  background-color: var(--bg-secondary);
}

.theme-toggle svg {
  width: 24px;
  height: 24px;
  fill: var(--text-color);
}

.sun-icon {
  display: none;
}

.moon-icon {
  display: block;
}

[data-theme="dark"] .sun-icon {
  display: block;
}

[data-theme="dark"] .moon-icon {
  display: none;
}

/* Intro section */
.intro-section {
  text-align: center;
  margin-bottom: var(--spacing-xl);
  max-width: 800px;
  margin-left: auto;
  margin-right: auto;
}

/* Main content layout */
.app-content {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--spacing-xl);
  margin-bottom: var(--spacing-xl);
}

@media (max-width: 768px) {
  .app-content {
    grid-template-columns: 1fr;
  }
}

/* Panels */
.left-panel, .right-panel {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-xl);
}

/* Sections */
section {
  background-color: var(--bg-panel);
  border-radius: var(--border-radius-lg);
  padding: var(--spacing-lg);
  box-shadow: var(--shadow-md);
  transition: background-color var(--transition-normal), box-shadow var(--transition-normal);
}

/* Frequency selection */
.frequency-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: var(--spacing-md);
}

.frequency-item {
  display: flex;
  align-items: center;
  padding: var(--spacing-md);
  border-radius: var(--border-radius-md);
  background-color: var(--bg-secondary);
  transition: background-color var(--transition-fast);
  cursor: pointer;
}

.frequency-item:hover {
  background-color: var(--bg-color);
}

.frequency-item.active {
  background-color: var(--primary-color);
  color: white;
}

.frequency-item input[type="checkbox"] {
  margin-right: var(--spacing-md);
  appearance: none;
  width: 20px;
  height: 20px;
  border: 2px solid var(--border-color);
  border-radius: var(--border-radius-sm);
  position: relative;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.frequency-item input[type="checkbox"]:checked {
  background-color: var(--primary-color);
  border-color: var(--primary-color);
}

.frequency-item input[type="checkbox"]:checked::after {
  content: '';
  position: absolute;
  top: 2px;
  left: 6px;
  width: 5px;
  height: 10px;
  border: solid white;
  border-width: 0 2px 2px 0;
  transform: rotate(45deg);
}

.frequency-item .frequency-info {
  flex: 1;
}

.frequency-item .frequency-value {
  font-weight: 600;
  margin-right: var(--spacing-xs);
}

.frequency-item .frequency-description {
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
}

.frequency-item.active .frequency-description {
  color: rgba(255, 255, 255, 0.8);
}

/* Session controls */
.control-group {
  margin-bottom: var(--spacing-md);
}

.control-group label {
  display: block;
  margin-bottom: var(--spacing-xs);
  font-weight: 500;
}

.control-group input[type="range"] {
  width: 100%;
  height: 6px;
  -webkit-appearance: none;
  appearance: none;
  background: var(--bg-secondary);
  border-radius: 3px;
  outline: none;
  margin-bottom: var(--spacing-xs);
}

.control-group input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: var(--primary-color);
  cursor: pointer;
  transition: background var(--transition-fast);
}

.control-group input[type="range"]::-webkit-slider-thumb:hover {
  background: var(--primary-light);
}

.control-group select {
  width: 100%;
  padding: var(--spacing-sm);
  border-radius: var(--border-radius-md);
  border: 1px solid var(--border-color);
  background-color: var(--bg-secondary);
  color: var(--text-color);
  font-family: var(--font-family);
  font-size: var(--font-size-md);
  cursor: pointer;
  transition: border-color var(--transition-fast);
}

.control-group select:focus {
  border-color: var(--primary-color);
  outline: none;
}

.timer-display {
  text-align: center;
  font-size: var(--font-size-xl);
  font-weight: 600;
  margin: var(--spacing-md) 0;
  color: var(--primary-color);
}

.control-buttons {
  display: flex;
  gap: var(--spacing-md);
  margin-top: var(--spacing-md);
}

button {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--spacing-xs);
  padding: var(--spacing-sm) var(--spacing-md);
  border-radius: var(--border-radius-md);
  font-family: var(--font-family);
  font-size: var(--font-size-md);
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition-fast);
  border: none;
}

button svg {
  width: 20px;
  height: 20px;
  fill: currentColor;
}

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

.primary-btn:hover {
  background-color: var(--primary-light);
}

.primary-btn:disabled {
  background-color: var(--text-tertiary);
  cursor: not-allowed;
}

.secondary-btn {
  background-color: var(--bg-secondary);
  color: var(--text-color);
}

.secondary-btn:hover {
  background-color: var(--border-color);
}

.secondary-btn:disabled {
  color: var(--text-tertiary);
  cursor: not-allowed;
}

.tertiary-btn {
  background-color: transparent;
  color: var(--primary-color);
  border: 1px solid var(--primary-color);
}

.tertiary-btn:hover {
  background-color: var(--primary-color);
  color: white;
}

/* Visualization */
.visualization-container {
  width: 100%;
  height: 200px;
  background-color: var(--bg-secondary);
  border-radius: var(--border-radius-md);
  overflow: hidden;
  margin-bottom: var(--spacing-md);
}

.active-frequency {
  text-align: center;
  font-size: var(--font-size-md);
  color: var(--text-secondary);
}

#current-frequency {
  font-weight: 600;
  color: var(--primary-color);
}

/* Effects section */
.effects-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(150px, 1fr));
  gap: var(--spacing-md);
}

.effect-item {
  display: flex;
  align-items: center;
  padding: var(--spacing-sm);
  border-radius: var(--border-radius-md);
  background-color: var(--bg-secondary);
  transition: background-color var(--transition-fast);
  cursor: pointer;
}

.effect-item:hover {
  background-color: var(--bg-color);
}

.effect-item.active {
  background-color: var(--secondary-color);
  color: white;
}

.effect-item input[type="checkbox"] {
  margin-right: var(--spacing-sm);
  appearance: none;
  width: 18px;
  height: 18px;
  border: 2px solid var(--border-color);
  border-radius: var(--border-radius-sm);
  position: relative;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.effect-item input[type="checkbox"]:checked {
  background-color: var(--secondary-color);
  border-color: var(--secondary-color);
}

.effect-item input[type="checkbox"]:checked::after {
  content: '';
  position: absolute;
  top: 2px;
  left: 5px;
  width: 5px;
  height: 9px;
  border: solid white;
  border-width: 0 2px 2px 0;
  transform: rotate(45deg);
}

/* Presets section */
.presets-container {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
}

.preset-card {
  padding: var(--spacing-md);
  border-radius: var(--border-radius-md);
  background-color: var(--bg-secondary);
  transition: background-color var(--transition-fast);
  cursor: pointer;
}

.preset-card:hover {
  background-color: var(--bg-color);
}

.preset-card h4 {
  margin-bottom: var(--spacing-xs);
}

.preset-card p {
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
  margin-bottom: var(--spacing-sm);
}

.preset-card .preset-frequencies {
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-xs);
  margin-bottom: var(--spacing-sm);
}

.preset-card .preset-frequency {
  font-size: var(--font-size-xs);
  background-color: var(--primary-color);
  color: white;
  padding: 2px 6px;
  border-radius: var(--border-radius-sm);
}

.preset-card .preset-actions {
  display: flex;
  justify-content: flex-end;
  gap: var(--spacing-sm);
}

.preset-card .preset-actions button {
  padding: var(--spacing-xs) var(--spacing-sm);
  font-size: var(--font-size-xs);
}

.no-presets-message {
  color: var(--text-tertiary);
  text-align: center;
  font-style: italic;
}

/* Frequency info section */
.frequency-info {
  margin-top: var(--spacing-xl);
}

.frequency-cards {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: var(--spacing-md);
  margin-top: var(--spacing-md);
}

.frequency-card {
  padding: var(--spacing-md);
  border-radius: var(--border-radius-md);
  background-color: var(--bg-panel);
  box-shadow: var(--shadow-sm);
  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
}

.frequency-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
}

.frequency-card h4 {
  color: var(--primary-color);
  margin-bottom: var(--spacing-xs);
}

.frequency-card p {
  font-size: var(--font-size-sm);
  margin-bottom: 0;
}

/* Footer */
footer {
  margin-top: var(--spacing-xl);
  padding: var(--spacing-lg) 0;
  border-top: 1px solid var(--border-color);
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
}

.language-selector {
  display: flex;
  align-items: center;
  gap: var(--spacing-md);
}

.language-selector select {
  padding: var(--spacing-xs) var(--spacing-sm);
  border-radius: var(--border-radius-md);
  border: 1px solid var(--border-color);
  background-color: var(--bg-secondary);
  color: var(--text-color);
  font-family: var(--font-family);
  font-size: var(--font-size-sm);
  cursor: pointer;
}

.footer-links {
  display: flex;
  gap: var(--spacing-lg);
  justify-content: center;
}

.copyright {
  text-align: center;
  font-size: var(--font-size-sm);
  color: var(--text-tertiary);
}

/* Modals */
.modal {
  display: none;
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: rgba(0, 0, 0, 0.5);
  z-index: var(--z-index-modal);
  align-items: center;
  justify-content: center;
}

.modal.active {
  display: flex;
}

.modal-content {
  background-color: var(--bg-panel);
  border-radius: var(--border-radius-lg);
  padding: var(--spacing-lg);
  width: 90%;
  max-width: 500px;
  max-height: 90vh;
  overflow-y: auto;
  position: relative;
}

.close-modal {
  position: absolute;
  top: var(--spacing-md);
  right: var(--spacing-md);
  font-size: var(--font-size-xl);
  cursor: pointer;
  color: var(--text-tertiary);
  transition: color var(--transition-fast);
}

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

.form-group {
  margin-bottom: var(--spacing-md);
}

.form-group label {
  display: block;
  margin-bottom: var(--spacing-xs);
  font-weight: 500;
}

.form-group input,
.form-group textarea {
  width: 100%;
  padding: var(--spacing-sm);
  border-radius: var(--border-radius-md);
  border: 1px solid var(--border-color);
  background-color: var(--bg-secondary);
  color: var(--text-color);
  font-family: var(--font-family);
  font-size: var(--font-size-md);
  transition: border-color var(--transition-fast);
}

.form-group input:focus,
.form-group textarea:focus {
  border-color: var(--primary-color);
  outline: none;
}

.form-group textarea {
  min-height: 100px;
  resize: vertical;
}

/* Responsive adjustments */
@media (max-width: 576px) {
  :root {
    --font-size-xxl: 1.75rem;
    --font-size-xl: 1.25rem;
    --font-size-lg: 1.125rem;
  }
  
  .app-container {
    padding: var(--spacing-sm);
  }
  
  section {
    padding: var(--spacing-md);
  }
  
  .frequency-grid,
  .effects-grid,
  .frequency-cards {
    grid-template-columns: 1fr;
  }
  
  .control-buttons {
    flex-direction: column;
  }
  
  .footer-links {
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-md);
  }
}