/* ========================================
   Drone Fuel Calculator - Main Styles
   ======================================== */

/* CSS Variables */
:root {
  /* Colors */
  --color-primary: #2563eb;
  --color-primary-dark: #1e40af;
  --color-primary-light: #3b82f6;
  --color-secondary: #64748b;
  --color-success: #10b981;
  --color-warning: #f59e0b;
  --color-error: #ef4444;
  --color-info: #3b82f6;
  --color-caution: #eab308;

  /* Backgrounds */
  --bg-primary: #f8fafc;
  --bg-surface: #ffffff;
  --bg-hover: #f1f5f9;
  --bg-active: #e2e8f0;

  /* Text */
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #94a3b8;
  --text-inverse: #ffffff;

  /* Borders */
  --border-color: #e2e8f0;
  --border-color-focus: var(--color-primary);
  --border-radius: 6px;
  --border-radius-lg: 8px;

  /* Spacing */
  --spacing-xs: 4px;
  --spacing-sm: 8px;
  --spacing-md: 16px;
  --spacing-lg: 24px;
  --spacing-xl: 32px;
  --spacing-2xl: 48px;

  /* Typography */
  --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  --font-size-sm: 0.875rem;
  --font-size-base: 1rem;
  --font-size-lg: 1.125rem;
  --font-size-xl: 1.25rem;
  --font-size-2xl: 1.5rem;
  --font-size-3xl: 2rem;

  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-base: 200ms ease;
  --transition-slow: 300ms ease;
}

/* Dark Mode Variables */
[data-theme="dark"] {
  /* Colors - keep primary colors the same for brand consistency */
  --color-primary: #3b82f6;
  --color-primary-dark: #60a5fa;
  --color-primary-light: #2563eb;
  --color-secondary: #94a3b8;
  --color-success: #10b981;
  --color-warning: #fbbf24;
  --color-error: #f87171;
  --color-info: #60a5fa;
  --color-caution: #fbbf24;

  /* Backgrounds */
  --bg-primary: #0f172a;
  --bg-surface: #1e293b;
  --bg-hover: #334155;
  --bg-active: #475569;

  /* Text */
  --text-primary: #f1f5f9;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;
  --text-inverse: #0f172a;

  /* Borders */
  --border-color: #334155;
  --border-color-focus: var(--color-primary);

  /* Shadows - softer in dark mode */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.5);
}

/* ========================================
   Reset & Base Styles
   ======================================== */

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

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

body {
  font-family: var(--font-family);
  font-size: var(--font-size-base);
  line-height: 1.5;
  color: var(--text-primary);
  background-color: var(--bg-primary);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ========================================
   Typography
   ======================================== */

h1, h2, h3, h4, h5, h6 {
  line-height: 1.2;
  font-weight: 600;
  margin-bottom: var(--spacing-md);
}

h1 {
  font-size: var(--font-size-3xl);
  font-weight: 700;
}

h2 {
  font-size: var(--font-size-2xl);
}

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

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

/* ========================================
   Header
   ======================================== */

.app-header {
  background-color: var(--color-primary);
  color: var(--text-inverse);
  padding: var(--spacing-lg) var(--spacing-md);
  text-align: center;
  box-shadow: var(--shadow-md);
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--spacing-lg);
  position: relative;
}

.header-logo {
  height: 60px;
  width: auto;
  object-fit: contain;
  position: absolute;
  left: var(--spacing-lg);
}

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

.app-header h1 {
  margin-bottom: var(--spacing-sm);
  font-size: var(--font-size-2xl);
}

.subtitle {
  font-size: var(--font-size-base);
  opacity: 0.9;
  margin: 0;
}

/* ========================================
   Container
   ======================================== */

.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: var(--spacing-lg);
  flex: 1;
}

/* ========================================
   Tab Navigation
   ======================================== */

.tab-nav {
  display: flex;
  gap: var(--spacing-sm);
  margin-bottom: var(--spacing-lg);
  border-bottom: 2px solid var(--border-color);
  flex-wrap: wrap;
}

.tab-btn {
  background: none;
  border: none;
  padding: var(--spacing-md) var(--spacing-lg);
  font-size: var(--font-size-base);
  font-weight: 500;
  color: var(--text-secondary);
  cursor: pointer;
  border-bottom: 3px solid transparent;
  transition: all var(--transition-base);
  position: relative;
  bottom: -2px;
}

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

.tab-btn.active {
  color: var(--color-primary);
  border-bottom-color: var(--color-primary);
}

.tab-btn:focus {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

.tab-name {
  display: inline-block;
}

.compare-btn {
  margin-left: auto;
  background-color: var(--color-success);
  color: var(--text-inverse);
  border: none;
  padding: var(--spacing-sm) var(--spacing-lg);
  font-size: var(--font-size-base);
  font-weight: 500;
  border-radius: var(--border-radius);
  cursor: pointer;
  transition: background-color var(--transition-base);
}

.compare-btn:hover:not(:disabled) {
  background-color: #059669;
}

.compare-btn:disabled {
  background-color: var(--bg-active);
  color: var(--text-muted);
  cursor: not-allowed;
}

.compare-btn:focus {
  outline: 2px solid var(--color-success);
  outline-offset: 2px;
}

/* ========================================
   Tab Content
   ======================================== */

.tab-content {
  display: none;
}

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

/* ========================================
   Form Sections
   ======================================== */

.calculator-form section {
  background-color: var(--bg-surface);
  border-radius: var(--border-radius-lg);
  padding: var(--spacing-lg);
  margin-bottom: var(--spacing-lg);
  box-shadow: var(--shadow-sm);
}

.calculator-form section h2 {
  color: var(--text-primary);
  margin-bottom: var(--spacing-lg);
  padding-bottom: var(--spacing-md);
  border-bottom: 2px solid var(--border-color);
}

/* ========================================
   Input Section
   ======================================== */

.input-section {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--spacing-md);
}

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

.input-group label {
  font-size: var(--font-size-sm);
  font-weight: 500;
  color: var(--text-primary);
  margin-bottom: var(--spacing-sm);
}

.optional {
  color: var(--text-muted);
  font-weight: 400;
  font-size: var(--font-size-sm);
}

.calc-input {
  padding: 12px 16px;
  border: 1px solid var(--border-color);
  border-radius: var(--border-radius);
  font-size: var(--font-size-base);
  font-family: var(--font-family);
  transition: border-color var(--transition-fast);
  background-color: var(--bg-surface);
  min-height: 44px;
}

.calc-input:focus {
  outline: none;
  border-color: var(--border-color-focus);
  border-width: 2px;
  padding: 11px 15px;
}

.calc-input:hover:not(:focus) {
  border-color: var(--color-secondary);
}

.calc-input.error {
  border-color: var(--color-error);
}

.help-text {
  font-size: var(--font-size-sm);
  color: var(--text-muted);
  margin-top: var(--spacing-xs);
}

.calculated-value {
  color: var(--color-info);
  font-weight: 500;
}

.error-message {
  font-size: var(--font-size-sm);
  color: var(--color-error);
  margin-top: var(--spacing-xs);
  display: none;
}

.error-message.show {
  display: block;
}

/* ========================================
   Output Section
   ======================================== */

.output-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: var(--spacing-md);
}

.output-item {
  padding: var(--spacing-md);
  background-color: var(--bg-hover);
  border-radius: var(--border-radius);
  border-left: 4px solid var(--color-secondary);
}

.output-item.total {
  border-left-color: var(--color-primary);
  background-color: #dbeafe;
}

.output-item label {
  display: block;
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
  margin-bottom: var(--spacing-sm);
  font-weight: 500;
}

.output-value {
  font-size: var(--font-size-2xl);
  font-weight: 700;
  color: var(--text-primary);
}

.output-item.total .output-value {
  font-size: 2.5rem;
  color: var(--color-primary);
}

.output-value .unit {
  font-size: var(--font-size-base);
  font-weight: 400;
  color: var(--text-secondary);
  margin-left: var(--spacing-xs);
}

/* ========================================
   Warnings Section
   ======================================== */

.warnings-section {
  display: none;
}

.warnings-section.has-warnings {
  display: block;
}

.warning-alert {
  display: flex;
  align-items: flex-start;
  gap: var(--spacing-md);
  padding: var(--spacing-md);
  border-radius: var(--border-radius);
  margin-bottom: var(--spacing-md);
  border-left: 4px solid;
}

.warning-alert:last-child {
  margin-bottom: 0;
}

.warning-alert.info {
  background-color: #dbeafe;
  border-left-color: var(--color-info);
  color: #1e3a8a;
}

.warning-alert.caution {
  background-color: #fef3c7;
  border-left-color: var(--color-caution);
  color: #78350f;
}

.warning-alert.warning {
  background-color: #fed7aa;
  border-left-color: var(--color-warning);
  color: #7c2d12;
}

.warning-alert.error {
  background-color: #fecaca;
  border-left-color: var(--color-error);
  color: #7f1d1d;
}

.warning-icon {
  font-size: var(--font-size-xl);
  flex-shrink: 0;
}

.warning-message {
  flex: 1;
  font-size: var(--font-size-sm);
  line-height: 1.6;
}

/* ========================================
   Actions Section
   ======================================== */

.actions-section {
  display: flex;
  gap: var(--spacing-md);
  flex-wrap: wrap;
}

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

button {
  font-family: var(--font-family);
  font-size: var(--font-size-base);
  font-weight: 500;
  border-radius: var(--border-radius);
  padding: 12px 24px;
  cursor: pointer;
  transition: all var(--transition-base);
  min-height: 44px;
  border: none;
}

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

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

.btn-primary:active {
  background-color: #1e3a8a;
}

.btn-primary:focus {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

.btn-secondary {
  background-color: var(--bg-surface);
  color: var(--text-primary);
  border: 1px solid var(--border-color);
}

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

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

.btn-secondary:focus {
  outline: 2px solid var(--color-secondary);
  outline-offset: 2px;
}

/* ========================================
   Comparison View
   ======================================== */

.comparison-view {
  background-color: var(--bg-surface);
  border-radius: var(--border-radius-lg);
  padding: var(--spacing-lg);
  box-shadow: var(--shadow-md);
}

.comparison-view.hidden {
  display: none;
}

.comparison-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: var(--spacing-lg);
  padding-bottom: var(--spacing-md);
  border-bottom: 2px solid var(--border-color);
}

.comparison-header h2 {
  margin: 0;
}

.comparison-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--spacing-xl);
  margin-bottom: var(--spacing-lg);
}

.comparison-column h3 {
  color: var(--color-primary);
  margin-bottom: var(--spacing-md);
  padding-bottom: var(--spacing-sm);
  border-bottom: 2px solid var(--border-color);
}

.comparison-row {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: var(--spacing-md);
  padding: var(--spacing-sm) 0;
  border-bottom: 1px solid var(--border-color);
}

.comparison-row:last-child {
  border-bottom: none;
}

.comparison-label {
  font-weight: 500;
  color: var(--text-secondary);
  font-size: var(--font-size-sm);
}

.comparison-value {
  font-weight: 600;
  color: var(--text-primary);
  text-align: right;
}

.comparison-value.difference {
  color: var(--color-warning);
  font-size: var(--font-size-sm);
}

.comparison-actions {
  display: flex;
  gap: var(--spacing-md);
  justify-content: flex-end;
  flex-wrap: wrap;
}

/* ========================================
   Footer
   ======================================== */

.app-footer {
  background-color: var(--bg-surface);
  border-top: 1px solid var(--border-color);
  padding: var(--spacing-lg);
  text-align: center;
  margin-top: auto;
}

.disclaimer {
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
  max-width: 800px;
  margin: 0 auto var(--spacing-md);
  line-height: 1.6;
}

.version {
  font-size: var(--font-size-sm);
  color: var(--text-muted);
  margin: 0;
}

.footer-link {
  color: var(--color-primary);
  text-decoration: none;
  transition: color 0.2s ease;
}

.footer-link:hover {
  color: var(--color-primary-dark);
  text-decoration: underline;
}

.footer-link:focus {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
  border-radius: 2px;
}

/* ========================================
   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-width: 0;
}

/* ========================================
   Focus Visible (Accessibility)
   ======================================== */

*:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

/* ========================================
   Loading State
   ======================================== */

.loading {
  pointer-events: none;
  opacity: 0.6;
}

/* ========================================
   Dark Mode Toggle
   ======================================== */

.theme-toggle {
  position: absolute;
  right: var(--spacing-lg);
  top: 50%;
  transform: translateY(-50%);
  background: rgba(255, 255, 255, 0.2);
  border: 1px solid rgba(255, 255, 255, 0.3);
  border-radius: 20px;
  padding: 8px 16px;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--text-inverse);
  font-size: var(--font-size-sm);
  transition: all var(--transition-base);
}

.theme-toggle:hover {
  background: rgba(255, 255, 255, 0.3);
  transform: translateY(-50%) scale(1.05);
}

.theme-toggle:active {
  transform: translateY(-50%) scale(0.98);
}

.theme-icon {
  font-size: 1.2rem;
  line-height: 1;
}

.theme-label {
  font-weight: 500;
  user-select: none;
}