/* ==========================================================================
   GST Calculator - Modern SaaS Minimalist Theme (Linear / Vercel style)
   ========================================================================== */

:root {
  --font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  
  /* Color Palette - Light Mode */
  --bg-main: #fafafa;
  --bg-subtle: #f4f4f5;
  --bg-card: #ffffff;
  --border-color: #e4e4e7;
  --border-hover: #d4d4d8;
  
  --text-primary: #09090b;
  --text-secondary: #71717a;
  --text-muted: #a1a1aa;
  
  /* SaaS Accent - Neutral Black / Linear Dark Green */
  --accent-primary: #18181b;
  --accent-hover: #27272a;
  --accent-text: #ffffff;
  
  --color-green: #10b981;
  --color-green-bg: #ecfdf5;
  --color-blue: #0284c7;
  --color-blue-bg: #f0f9ff;
  --color-danger: #ef4444;

  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.07), 0 2px 4px -2px rgba(0, 0, 0, 0.05);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.08), 0 4px 6px -4px rgba(0, 0, 0, 0.04);
  
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-full: 9999px;
  
  --transition: 0.15s ease;
}

/* Dark Theme Variables */
[data-theme="dark"] {
  --bg-main: #09090b;
  --bg-subtle: #121215;
  --bg-card: #18181b;
  --border-color: #27272a;
  --border-hover: #3f3f46;
  
  --text-primary: #f4f4f5;
  --text-secondary: #a1a1aa;
  --text-muted: #71717a;
  
  --accent-primary: #ffffff;
  --accent-hover: #e4e4e7;
  --accent-text: #09090b;
  
  --color-green: #34d399;
  --color-green-bg: rgba(16, 185, 129, 0.12);
  --color-blue: #38bdf8;
  --color-blue-bg: rgba(2, 132, 199, 0.12);
  
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.4);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.5);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.6);
}

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

html {
  font-family: var(--font-family);
  font-size: 15px;
  scroll-behavior: smooth;
  color-scheme: light dark;
}

body {
  background-color: var(--bg-main);
  color: var(--text-primary);
  line-height: 1.5;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  transition: background-color var(--transition), color var(--transition);
}

a {
  color: inherit;
  text-decoration: none;
}

button, input, select {
  font-family: inherit;
  font-size: inherit;
  color: inherit;
}

.container {
  max-width: 1180px;
  margin: 0 auto;
  padding: 0 1.5rem;
}

.max-w-3xl {
  max-width: 768px;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  border: 0;
}

.hidden {
  display: none !important;
}

/* ==========================================================================
   Header & Navigation
   ========================================================================== */

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: var(--bg-main);
  border-bottom: 1px solid var(--border-color);
  backdrop-filter: blur(12px);
}

.header-container {
  max-width: 1180px;
  margin: 0 auto;
  height: 60px;
  padding: 0 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: -0.01em;
}

.brand-icon {
  width: 32px;
  height: 32px;
  border-radius: var(--radius-md);
  background: var(--accent-primary);
  color: var(--accent-text);
  display: flex;
  align-items: center;
  justify-content: center;
}

.nav-desktop {
  display: flex;
  align-items: center;
  gap: 1.75rem;
}

.nav-link {
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--text-secondary);
  transition: color var(--transition);
}

.nav-link:hover {
  color: var(--text-primary);
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.btn-icon {
  width: 36px;
  height: 36px;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  background: var(--bg-card);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  color: var(--text-secondary);
  transition: var(--transition);
}

.btn-icon:hover {
  border-color: var(--border-hover);
  color: var(--text-primary);
}

.mobile-menu-btn {
  display: none;
}

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

.mobile-nav {
  display: flex;
  flex-direction: column;
  padding: 1rem 1.5rem;
  background: var(--bg-card);
  border-bottom: 1px solid var(--border-color);
  gap: 0.75rem;
}

.mobile-nav-link {
  font-weight: 500;
  color: var(--text-secondary);
  padding: 0.5rem 0;
}

/* ==========================================================================
   Hero Section
   ========================================================================== */

.hero-section {
  padding: 4rem 1.5rem 2.5rem;
  text-align: center;
}

.hero-content {
  max-width: 720px;
  margin: 0 auto;
}

.badge {
  display: inline-flex;
  align-items: center;
  font-size: 0.75rem;
  font-weight: 600;
  padding: 0.25rem 0.75rem;
  border-radius: var(--radius-full);
  background: var(--bg-subtle);
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  margin-bottom: 1.25rem;
  letter-spacing: 0.03em;
  text-transform: uppercase;
}

.hero-title {
  font-size: 2.75rem;
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.15;
  color: var(--text-primary);
  margin-bottom: 1rem;
}

.hero-subtitle {
  font-size: 1.1rem;
  color: var(--text-secondary);
  margin-bottom: 2rem;
  font-weight: 400;
}

.hero-cta {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
}

.trust-badge {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  font-size: 0.8rem;
  color: var(--text-secondary);
}

.trust-badge svg {
  color: var(--color-green);
}

/* ==========================================================================
   Dashboard Quick Stats
   ========================================================================== */

.stats-section {
  margin-bottom: 2.5rem;
}

.stats-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1rem;
}

.stat-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1rem 1.25rem;
  box-shadow: var(--shadow-sm);
}

.stat-label {
  font-size: 0.75rem;
  font-weight: 500;
  color: var(--text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.03em;
  margin-bottom: 0.35rem;
}

.stat-value {
  font-size: 1.35rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--text-primary);
}

/* ==========================================================================
   Calculator Grid & Form Cards
   ========================================================================== */

.calculator-section {
  padding-bottom: 4rem;
}

.calculator-grid {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 1.5rem;
  align-items: start;
}

.card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 1.75rem;
  box-shadow: var(--shadow-sm);
}

.card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 1.5rem;
  padding-bottom: 0.75rem;
  border-bottom: 1px solid var(--border-color);
}

.card-title {
  font-size: 1.15rem;
  font-weight: 700;
  letter-spacing: -0.01em;
}

/* Form Styles */
.form-group {
  margin-bottom: 1.25rem;
}

.form-label {
  display: block;
  font-size: 0.825rem;
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: 0.4rem;
}

.form-row {
  display: flex;
  gap: 1rem;
}

.flex-1 { flex: 1; }

.tab-group {
  display: flex;
  background: var(--bg-subtle);
  padding: 3px;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  gap: 3px;
}

.tab-btn {
  flex: 1;
  padding: 0.45rem 0.5rem;
  background: transparent;
  border: none;
  border-radius: var(--radius-sm);
  font-size: 0.825rem;
  font-weight: 500;
  color: var(--text-secondary);
  cursor: pointer;
  transition: var(--transition);
}

.tab-btn.active {
  background: var(--bg-card);
  color: var(--text-primary);
  font-weight: 600;
  box-shadow: var(--shadow-sm);
}

.input-prefix-wrapper {
  position: relative;
  display: flex;
  align-items: center;
}

.input-prefix {
  position: absolute;
  left: 0.85rem;
  font-weight: 600;
  color: var(--text-muted);
}

.form-input, .form-select {
  width: 100%;
  padding: 0.6rem 0.85rem;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  background: var(--bg-card);
  color: var(--text-primary);
  font-size: 0.95rem;
  outline: none;
  transition: border-color var(--transition), box-shadow var(--transition);
}

.input-prefix-wrapper .form-input {
  padding-left: 2.25rem;
}

.form-input:focus, .form-select:focus {
  border-color: var(--accent-primary);
  box-shadow: 0 0 0 1px var(--accent-primary);
}

.input-error {
  display: block;
  font-size: 0.75rem;
  color: var(--color-danger);
  margin-top: 0.35rem;
}

.rate-chips {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.5rem;
  margin-bottom: 0.5rem;
}

.rate-chip {
  padding: 0.45rem 0.5rem;
  background: var(--bg-subtle);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-secondary);
  cursor: pointer;
  transition: var(--transition);
}

.rate-chip:hover {
  border-color: var(--border-hover);
  color: var(--text-primary);
}

.rate-chip.active {
  background: var(--accent-primary);
  color: var(--accent-text);
  border-color: var(--accent-primary);
}

.custom-rate-input {
  margin-top: 0.5rem;
}

.form-actions {
  display: flex;
  gap: 0.75rem;
  margin-top: 1.5rem;
  padding-top: 1rem;
  border-top: 1px solid var(--border-color);
}

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

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.45rem;
  font-size: 0.875rem;
  font-weight: 600;
  padding: 0.6rem 1.25rem;
  border-radius: var(--radius-md);
  border: 1px solid transparent;
  cursor: pointer;
  transition: var(--transition);
}

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

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

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

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

.btn-outline {
  background: transparent;
  border-color: var(--border-color);
  color: var(--text-secondary);
}

.btn-outline:hover {
  color: var(--text-primary);
  border-color: var(--border-hover);
}

.btn-sm {
  padding: 0.4rem 0.75rem;
  font-size: 0.8rem;
}

.select-sm {
  padding: 0.3rem 0.5rem;
  font-size: 0.8rem;
  font-weight: 600;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  background: var(--bg-subtle);
}

/* ==========================================================================
   Result Card Presentation
   ========================================================================== */

.result-card {
  display: flex;
  flex-direction: column;
}

.pill-badge {
  font-size: 0.75rem;
  font-weight: 600;
  padding: 0.2rem 0.6rem;
  background: var(--color-blue-bg);
  color: var(--color-blue);
  border-radius: var(--radius-full);
}

.result-highlight {
  background: var(--bg-subtle);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  margin-bottom: 1.5rem;
}

.result-highlight-label {
  font-size: 0.775rem;
  font-weight: 600;
  text-transform: uppercase;
  color: var(--text-secondary);
  letter-spacing: 0.04em;
  margin-bottom: 0.25rem;
}

.result-highlight-value {
  font-size: 2.1rem;
  font-weight: 800;
  letter-spacing: -0.03em;
  color: var(--text-primary);
}

.summary-list {
  display: flex;
  flex-direction: column;
  gap: 0.65rem;
}

.summary-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: 0.9rem;
}

.summary-label {
  color: var(--text-secondary);
}

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

.tax-split .summary-label {
  font-size: 0.825rem;
  padding-left: 0.5rem;
}

.tax-split .summary-value {
  font-size: 0.85rem;
  color: var(--text-secondary);
}

.summary-divider {
  height: 1px;
  background: var(--border-color);
  margin: 0.5rem 0;
}

.highlight-subrow {
  padding-top: 0.35rem;
}

.highlight-subrow .summary-label {
  font-weight: 600;
  color: var(--text-primary);
}

.highlight-subrow .summary-value {
  font-size: 1rem;
  font-weight: 700;
}

.text-success { color: var(--color-green) !important; }
.text-accent { color: var(--color-blue) !important; }

.export-actions {
  display: flex;
  gap: 0.5rem;
  margin-top: 2rem;
  padding-top: 1rem;
  border-top: 1px solid var(--border-color);
}

.export-actions .btn {
  flex: 1;
}

/* ==========================================================================
   Multi-Item Invoice Section
   ========================================================================== */

.section {
  padding: 4rem 0;
}

.bg-subtle {
  background: var(--bg-subtle);
}

.section-header {
  margin-bottom: 2rem;
}

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

.section-title {
  font-size: 1.85rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  margin-bottom: 0.5rem;
}

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

.flex-between {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: 1rem;
}

.invoice-toolbar {
  display: flex;
  gap: 0.5rem;
  margin-bottom: 1.25rem;
}

.table-responsive {
  width: 100%;
  overflow-x: auto;
}

.invoice-table, .data-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.875rem;
}

.invoice-table th, .data-table th {
  text-align: left;
  padding: 0.75rem 0.65rem;
  border-bottom: 1px solid var(--border-color);
  font-weight: 600;
  color: var(--text-secondary);
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.invoice-table td, .data-table td {
  padding: 0.65rem;
  border-bottom: 1px solid var(--border-color);
}

.invoice-table input, .invoice-table select {
  width: 100%;
  padding: 0.35rem 0.5rem;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  background: var(--bg-main);
}

.invoice-footer {
  display: flex;
  justify-content: flex-end;
  margin-top: 1.5rem;
}

.invoice-totals-card {
  width: 100%;
  max-width: 360px;
  background: var(--bg-subtle);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.w-12 { width: 48px; }
.w-20 { width: 80px; }
.w-24 { width: 96px; }
.w-28 { width: 112px; }
.text-right { text-align: right; }
.text-center { text-align: center; }

.btn-remove-row {
  background: none;
  border: none;
  color: var(--text-muted);
  cursor: pointer;
  padding: 4px;
  border-radius: var(--radius-sm);
}

.btn-remove-row:hover {
  color: var(--color-danger);
}

.rate-badge {
  font-weight: 700;
  font-size: 0.8rem;
  padding: 0.2rem 0.5rem;
  background: var(--bg-subtle);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
}

.card-footer-note {
  padding: 1rem 1.25rem;
  border-top: 1px solid var(--border-color);
  font-size: 0.775rem;
  color: var(--text-secondary);
  background: var(--bg-card);
}

/* ==========================================================================
   History Section
   ========================================================================== */

.history-list {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.history-item {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1rem 1.25rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  box-shadow: var(--shadow-sm);
}

.history-details {
  display: flex;
  flex-direction: column;
  gap: 0.2rem;
}

.history-title {
  font-weight: 600;
  font-size: 0.95rem;
}

.history-meta {
  font-size: 0.775rem;
  color: var(--text-secondary);
}

.history-actions {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.empty-state {
  text-align: center;
  padding: 3rem 1.5rem;
  border: 1px dashed var(--border-color);
  border-radius: var(--radius-lg);
  color: var(--text-secondary);
}

.empty-icon {
  margin-bottom: 0.75rem;
  color: var(--text-muted);
}

/* ==========================================================================
   FAQ Accordion
   ========================================================================== */

.accordion {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.accordion-item {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  overflow: hidden;
}

.accordion-header {
  width: 100%;
  padding: 1.15rem 1.25rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: none;
  border: none;
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-primary);
  text-align: left;
  cursor: pointer;
}

.chevron {
  transition: transform var(--transition);
  color: var(--text-secondary);
}

.accordion-item.active .chevron {
  transform: rotate(180deg);
}

.accordion-content {
  display: none;
  padding: 0 1.25rem 1.25rem;
  color: var(--text-secondary);
  font-size: 0.9rem;
  line-height: 1.6;
}

.accordion-item.active .accordion-content {
  display: block;
}

.accordion-content code {
  background: var(--bg-subtle);
  padding: 0.15rem 0.35rem;
  border-radius: var(--radius-sm);
  font-size: 0.825rem;
  color: var(--text-primary);
}

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

.site-footer {
  margin-top: auto;
  border-top: 1px solid var(--border-color);
  background: var(--bg-card);
  padding: 3.5rem 0 2rem;
}

.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1.5fr;
  gap: 3rem;
  margin-bottom: 2.5rem;
}

.footer-description {
  font-size: 0.85rem;
  color: var(--text-secondary);
  margin-top: 0.85rem;
  max-width: 300px;
}

.footer-heading {
  font-size: 0.85rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  margin-bottom: 1rem;
}

.footer-links {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
  font-size: 0.875rem;
  color: var(--text-secondary);
}

.footer-links a:hover {
  color: var(--text-primary);
}

.footer-legal {
  font-size: 0.8rem;
  color: var(--text-secondary);
  line-height: 1.6;
  margin-bottom: 1rem;
}

.copyright {
  font-size: 0.8rem;
  color: var(--text-muted);
}

/* ==========================================================================
   Toast Notification
   ========================================================================== */

.toast {
  position: fixed;
  bottom: 1.5rem;
  right: 1.5rem;
  z-index: 100;
  padding: 0.75rem 1.25rem;
  background: var(--accent-primary);
  color: var(--accent-text);
  border-radius: var(--radius-md);
  font-size: 0.85rem;
  font-weight: 500;
  box-shadow: var(--shadow-lg);
  animation: slideUp 0.2s ease forwards;
}

@keyframes slideUp {
  from { transform: translateY(12px); opacity: 0; }
  to { transform: translateY(0); opacity: 1; }
}

/* ==========================================================================
   Print Stylesheet
   ========================================================================== */

@media print {
  body {
    background: #fff !important;
    color: #000 !important;
  }

  .site-header,
  .hero-section,
  .stats-section,
  .form-card,
  .export-actions,
  #rates,
  #history-section,
  #faq,
  .site-footer,
  .invoice-toolbar,
  .btn-remove-row,
  .toast {
    display: none !important;
  }

  .calculator-grid {
    display: block !important;
  }

  .result-card, .invoice-card {
    border: none !important;
    box-shadow: none !important;
    padding: 0 !important;
  }

  .card-header {
    border-bottom: 2px solid #000 !important;
  }

  .result-highlight {
    border: 1px solid #ccc !important;
    background: #f9f9f9 !important;
  }
}

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

@media (max-width: 960px) {
  .calculator-grid {
    grid-template-columns: 1fr;
  }
  
  .stats-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .footer-grid {
    grid-template-columns: 1fr;
    gap: 2rem;
  }
}

@media (max-width: 640px) {
  .hero-title {
    font-size: 2.1rem;
  }

  .nav-desktop {
    display: none;
  }

  .mobile-menu-btn {
    display: flex;
  }

  .stats-grid {
    grid-template-columns: 1fr;
  }

  .form-row {
    flex-direction: column;
    gap: 0;
  }

  .rate-chips {
    grid-template-columns: repeat(3, 1fr);
  }
}