/**
 * Zenith GST Calculator - Global Design System & Core Styles
 * Clean, modern, trustworthy financial utility styling.
 */

:root {
  /* Color Palette - Light Theme */
  --bg-body: #f8fafc;
  --bg-card: #ffffff;
  --bg-card-subtle: #f1f5f9;
  --bg-card-hover: #e2e8f0;
  --border-color: #e2e8f0;
  --border-color-focus: #3b82f6;

  --text-main: #0f172a;
  --text-muted: #475569;
  --text-light: #64748b;
  --text-inverse: #ffffff;

  /* Brand Accents */
  --primary: #1d4ed8;
  --primary-hover: #1e40af;
  --primary-light: #eff6ff;
  --primary-border: #bfdbfe;

  --success: #059669;
  --success-light: #ecfdf5;
  --warning: #d97706;
  --warning-light: #fffbeb;
  --danger: #dc2626;
  --danger-light: #fef2f2;

  /* Shadows & Radius */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.08), 0 2px 4px -2px rgba(0, 0, 0, 0.04);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.08), 0 4px 6px -4px rgba(0, 0, 0, 0.03);
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;
  --radius-full: 9999px;

  /* Typography */
  --font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --line-height: 1.6;

  /* Layout */
  --max-width: 1200px;
  --header-height: 70px;
  --transition-fast: 0.15s ease;
  --transition-normal: 0.25s ease;
}

/* Dark Theme Overrides */
[data-theme="dark"] {
  --bg-body: #090d16;
  --bg-card: #131b2e;
  --bg-card-subtle: #1a243b;
  --bg-card-hover: #222e4c;
  --border-color: #263554;
  --border-color-focus: #60a5fa;

  --text-main: #f8fafc;
  --text-muted: #cbd5e1;
  --text-light: #94a3b8;
  --text-inverse: #090d16;

  --primary: #3b82f6;
  --primary-hover: #60a5fa;
  --primary-light: #1e293b;
  --primary-border: #2563eb;

  --success: #10b981;
  --success-light: #064e3b;
  --warning: #f59e0b;
  --warning-light: #78350f;
  --danger: #ef4444;
  --danger-light: #7f1d1d;

  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.4);
  --shadow-md: 0 4px 8px -1px rgba(0, 0, 0, 0.5), 0 2px 4px -2px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 10px 20px -3px rgba(0, 0, 0, 0.6), 0 4px 6px -4px rgba(0, 0, 0, 0.4);
}

/* Base Reset */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-family);
  background-color: var(--bg-body);
  color: var(--text-main);
  line-height: var(--line-height);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  overflow-x: hidden;
  transition: background-color var(--transition-normal), color var(--transition-normal);
}

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

a:hover {
  text-decoration: underline;
}

button {
  font-family: inherit;
  cursor: pointer;
  border: none;
  outline: none;
  background: none;
}

input, select, textarea {
  font-family: inherit;
  font-size: 1rem;
}

/* Accessibility Focus Ring */
button:focus-visible,
input:focus-visible,
a:focus-visible {
  outline: 2px solid var(--border-color-focus);
  outline-offset: 2px;
}

/* Layout Container */
.container {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.25rem;
}

/* Header & Navigation */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--header-height);
  background-color: var(--bg-card);
  border-bottom: 1px solid var(--border-color);
  box-shadow: var(--shadow-sm);
  transition: background-color var(--transition-normal), border-color var(--transition-normal);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--text-main);
  text-decoration: none;
}

.brand-icon {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  background: linear-gradient(135deg, var(--primary), #4338ca);
  color: #ffffff;
  border-radius: var(--radius-sm);
  font-size: 1.1rem;
  font-weight: 800;
}

.brand-logo {
  width: 36px;
  height: 36px;
  object-fit: contain;
  border-radius: var(--radius-sm);
  display: block;
  flex-shrink: 0;
}

.brand:hover {
  text-decoration: none;
}

.brand-tag {
  color: var(--primary);
}

.nav-container {
  display: flex;
  align-items: center;
  gap: 1.5rem;
}

.site-nav {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  list-style: none;
}

.nav-link {
  display: inline-block;
  padding: 0.5rem 0.85rem;
  font-size: 0.95rem;
  font-weight: 500;
  color: var(--text-muted);
  border-radius: var(--radius-sm);
  transition: color var(--transition-fast), background-color var(--transition-fast);
}

.nav-link:hover {
  color: var(--primary);
  background-color: var(--bg-card-subtle);
  text-decoration: none;
}

.nav-link.active {
  color: var(--primary);
  font-weight: 600;
  background-color: var(--primary-light);
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.theme-toggle-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  background-color: var(--bg-card-subtle);
  color: var(--text-main);
  transition: background-color var(--transition-fast), border-color var(--transition-fast);
}

.theme-toggle-btn:hover {
  background-color: var(--bg-card-hover);
}

.icon-sun {
  display: none;
}

.icon-moon {
  display: block;
}

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

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

.nav-toggle-btn {
  display: none;
  align-items: center;
  justify-content: center;
  width: 42px;
  height: 42px;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  background-color: var(--bg-card-subtle);
  color: var(--text-main);
}

/* Hero Section */
.hero-section {
  padding: 2.25rem 0 1.5rem 0;
  text-align: center;
}

.hero-title {
  font-size: 2.35rem;
  font-weight: 800;
  letter-spacing: -0.025em;
  color: var(--text-main);
  margin-bottom: 0.5rem;
}

.hero-subtitle {
  font-size: 1.05rem;
  color: var(--text-muted);
  max-width: 650px;
  margin: 0 auto;
  line-height: 1.5;
}

.hero-badges {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.5rem;
  margin-top: 1rem;
}

.badge {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  font-size: 0.78rem;
  font-weight: 600;
  padding: 0.3rem 0.65rem;
  border-radius: var(--radius-full);
}

.badge-primary {
  background-color: var(--primary-light);
  color: var(--primary);
  border: 1px solid var(--primary-border);
}

.badge-warning {
  background-color: var(--warning-light);
  color: var(--warning);
  border: 1px solid rgba(217, 119, 6, 0.25);
}

.badge-neutral {
  background-color: var(--bg-card-subtle);
  color: var(--text-muted);
  border: 1px solid var(--border-color);
}

/* Content Sections */
.info-section {
  padding: 3.5rem 0;
}

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

.section-title {
  font-size: 1.75rem;
  font-weight: 700;
  color: var(--text-main);
  margin-bottom: 0.5rem;
  letter-spacing: -0.015em;
}

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

/* Informational Cards & Grid */
.cards-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 1.5rem;
}

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

.info-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.info-card-icon {
  width: 44px;
  height: 44px;
  border-radius: var(--radius-md);
  background-color: var(--primary-light);
  color: var(--primary);
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 1rem;
  font-size: 1.25rem;
}

.info-card h3 {
  font-size: 1.2rem;
  font-weight: 700;
  margin-bottom: 0.75rem;
  color: var(--text-main);
}

.info-card p {
  font-size: 0.95rem;
  color: var(--text-muted);
  line-height: 1.6;
  margin-bottom: 0.75rem;
}

.formula-box {
  background-color: var(--bg-card-subtle);
  border: 1px solid var(--border-color);
  border-left: 4px solid var(--primary);
  padding: 0.85rem 1rem;
  border-radius: var(--radius-sm);
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
  font-size: 0.88rem;
  color: var(--text-main);
  margin-top: 1rem;
}

/* Rate Slabs Table */
.table-wrapper {
  background-color: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  overflow-x: auto;
  margin-top: 1.5rem;
}

.rate-table {
  width: 100%;
  border-collapse: collapse;
  text-align: left;
  font-size: 0.95rem;
}

.rate-table th {
  background-color: var(--bg-card-subtle);
  color: var(--text-main);
  font-weight: 600;
  padding: 1rem 1.25rem;
  border-bottom: 1px solid var(--border-color);
}

.rate-table td {
  padding: 1rem 1.25rem;
  border-bottom: 1px solid var(--border-color);
  color: var(--text-muted);
}

.rate-table tr:last-child td {
  border-bottom: none;
}

.rate-table tr:hover td {
  background-color: var(--bg-card-subtle);
}

.rate-badge {
  display: inline-block;
  font-weight: 700;
  font-size: 0.85rem;
  padding: 0.25rem 0.6rem;
  border-radius: var(--radius-sm);
  background-color: var(--primary-light);
  color: var(--primary);
  border: 1px solid var(--primary-border);
}

/* FAQ Accordion */
.faq-container {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  max-width: 850px;
  margin: 0 auto;
}

.faq-item {
  background-color: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
  overflow: hidden;
  transition: border-color var(--transition-fast);
}

.faq-item.active {
  border-color: var(--primary-border);
}

.faq-question {
  width: 100%;
  padding: 1.25rem;
  text-align: left;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--text-main);
  background-color: var(--bg-card);
  transition: background-color var(--transition-fast);
}

.faq-question:hover {
  background-color: var(--bg-card-subtle);
}

.faq-chevron {
  flex-shrink: 0;
  transition: transform var(--transition-normal);
  color: var(--text-light);
}

.faq-item.active .faq-chevron {
  transform: rotate(180deg);
  color: var(--primary);
}

.faq-answer {
  max-height: 0;
  opacity: 0;
  overflow: hidden;
  transition: max-height 0.3s ease, opacity 0.25s ease, padding 0.25s ease;
  padding: 0 1.25rem;
  color: var(--text-muted);
  font-size: 0.95rem;
  line-height: 1.65;
}

.faq-item.active .faq-answer {
  max-height: 400px;
  opacity: 1;
  padding: 0 1.25rem 1.25rem 1.25rem;
}

/* Reserved AdSense Slot (Non-Intrusive, Production-Ready) */
.ad-slot-wrapper {
  margin: 2.5rem auto;
  max-width: 970px;
  padding: 0 1rem;
}

.ad-slot {
  min-height: 90px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  background-color: var(--bg-card-subtle);
  border: 1px dashed var(--border-color);
  border-radius: var(--radius-md);
  color: var(--text-light);
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: 0.5rem;
}

/* Toast Notification */
.toast {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  background-color: var(--text-main);
  color: var(--bg-card);
  padding: 0.85rem 1.35rem;
  border-radius: var(--radius-full);
  font-size: 0.9rem;
  font-weight: 600;
  box-shadow: var(--shadow-lg);
  transform: translateY(120%);
  opacity: 0;
  visibility: hidden;
  transition: transform 0.25s cubic-bezier(0.16, 1, 0.3, 1), opacity 0.25s ease, visibility 0.25s;
  z-index: 999;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.toast.show {
  transform: translateY(0);
  opacity: 1;
  visibility: visible;
}

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

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

.footer-brand p {
  margin-top: 0.75rem;
  font-size: 0.9rem;
  color: var(--text-muted);
  max-width: 320px;
  line-height: 1.55;
}

.footer-col h4 {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--text-main);
  margin-bottom: 1rem;
}

.footer-links {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.footer-links a {
  font-size: 0.88rem;
  color: var(--text-muted);
}

.footer-links a:hover {
  color: var(--primary);
  text-decoration: none;
}

.footer-bottom {
  padding-top: 2rem;
  border-top: 1px solid var(--border-color);
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  gap: 0.75rem;
  font-size: 0.84rem;
  color: var(--text-light);
}

.footer-disclaimer {
  max-width: 700px;
  font-size: 0.78rem;
  color: var(--text-light);
}