/* ==========================================================================
   GradeCalculating.com - Unified Design System & Component Library
   Designed for ultra-fast load times, dark/light modes, micro-interactions,
   and mobile-first ease of use. Zero dependencies.
   ========================================================================== */

:root {
  /* Core Color Palette - Vibrant Indigo/Teal Modern Aesthetic */
  --primary: #4f46e5;
  --primary-hover: #4338ca;
  --primary-light: #eef2ff;
  --primary-glow: rgba(79, 70, 229, 0.15);

  --accent: #06b6d4;
  --accent-hover: #0891b2;
  --accent-light: #ecfeff;

  --success: #10b981;
  --success-bg: #ecfdf5;
  --warning: #f59e0b;
  --warning-bg: #fffbeb;
  --danger: #ef4444;
  --danger-bg: #fef2f2;
  --info: #3b82f6;
  --info-bg: #eff6ff;

  /* Neutral Spectrum - Clean Slate */
  --bg-page: #f8fafc;
  --bg-surface: #ffffff;
  --bg-surface-elevated: #ffffff;
  --bg-subtle: #f1f5f9;
  --border-light: #e2e8f0;
  --border-strong: #cbd5e1;

  --text-main: #0f172a;
  --text-muted: #64748b;
  --text-light: #94a3b8;
  --text-inverse: #ffffff;

  /* Shadows */
  --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);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 8px 10px -6px rgba(0, 0, 0, 0.05);
  --shadow-focus: 0 0 0 3px rgba(79, 70, 229, 0.25);

  /* Radii */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  --radius-full: 9999px;

  /* Transitions */
  --trans-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
  --trans-normal: 250ms cubic-bezier(0.4, 0, 0.2, 1);
}

/* Dark Mode Theme */
[data-theme="dark"] {
  --bg-page: #0b0f19;
  --bg-surface: #111827;
  --bg-surface-elevated: #1f2937;
  --bg-subtle: #1e293b;
  --border-light: #1f2937;
  --border-strong: #334155;

  --text-main: #f8fafc;
  --text-muted: #94a3b8;
  --text-light: #64748b;

  --primary-light: rgba(79, 70, 229, 0.2);
  --accent-light: rgba(6, 182, 212, 0.15);
  --success-bg: rgba(16, 185, 129, 0.15);
  --warning-bg: rgba(245, 158, 11, 0.15);
  --danger-bg: rgba(239, 68, 68, 0.15);
  --info-bg: rgba(59, 130, 246, 0.15);

  --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);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.7);
}

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

html {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  font-size: 16px;
  line-height: 1.5;
  color: var(--text-main);
  background-color: var(--bg-page);
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
}

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

/* Header & Navigation */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background-color: var(--bg-surface);
  border-bottom: 1px solid var(--border-light);
  box-shadow: var(--shadow-sm);
  backdrop-filter: blur(8px);
}

.header-container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0.75rem 1.25rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.brand-link {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  text-decoration: none;
  color: var(--text-main);
  font-weight: 800;
  font-size: 1.25rem;
  letter-spacing: -0.02em;
}

.brand-icon {
  width: 32px;
  height: 32px;
  background: linear-gradient(135deg, var(--primary), var(--accent));
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-weight: 900;
  font-size: 1.1rem;
  box-shadow: 0 2px 8px var(--primary-glow);
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  list-style: none;
}

.nav-link {
  text-decoration: none;
  color: var(--text-muted);
  font-size: 0.925rem;
  font-weight: 500;
  padding: 0.4rem 0.75rem;
  border-radius: var(--radius-sm);
  transition: all var(--trans-fast);
}

.nav-link:hover, .nav-link.active {
  color: var(--primary);
  background-color: var(--primary-light);
}

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

.theme-toggle-btn {
  background: var(--bg-subtle);
  border: 1px solid var(--border-light);
  color: var(--text-muted);
  width: 38px;
  height: 38px;
  border-radius: var(--radius-full);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--trans-fast);
}

.theme-toggle-btn:hover {
  color: var(--text-main);
  background-color: var(--border-light);
}

/* Hero Section */
.hero-section {
  padding: 3rem 1.25rem 2rem;
  text-align: center;
  max-width: 900px;
  margin: 0 auto;
}

.hero-pill {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.35rem 0.9rem;
  background: var(--primary-light);
  color: var(--primary);
  border-radius: var(--radius-full);
  font-size: 0.825rem;
  font-weight: 600;
  margin-bottom: 1.25rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.hero-title {
  font-size: clamp(2.2rem, 4.5vw, 3.25rem);
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.15;
  color: var(--text-main);
  margin-bottom: 1rem;
}

.hero-title .gradient-text {
  background: linear-gradient(135deg, var(--primary), var(--accent));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.hero-desc {
  font-size: 1.125rem;
  color: var(--text-muted);
  max-width: 680px;
  margin: 0 auto;
}

/* Calculator Container & Tabbed Navigation */
.calc-wrapper {
  max-width: 1040px;
  margin: 0 auto 3rem;
  padding: 0 1.25rem;
}

.calc-tabs {
  display: flex;
  gap: 0.5rem;
  background: var(--bg-subtle);
  padding: 0.4rem;
  border-radius: var(--radius-lg);
  margin-bottom: 1.5rem;
  border: 1px solid var(--border-light);
  overflow-x: auto;
}

.calc-tab-btn {
  flex: 1;
  min-width: 140px;
  padding: 0.75rem 1rem;
  border: none;
  background: transparent;
  color: var(--text-muted);
  font-weight: 600;
  font-size: 0.95rem;
  border-radius: var(--radius-md);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  transition: all var(--trans-fast);
  white-space: nowrap;
}

.calc-tab-btn:hover {
  color: var(--text-main);
}

.calc-tab-btn.active {
  background: var(--bg-surface);
  color: var(--primary);
  box-shadow: var(--shadow-sm);
}

/* Main Interactive Tool Card */
.calc-card {
  background: var(--bg-surface);
  border-radius: var(--radius-xl);
  border: 1px solid var(--border-light);
  box-shadow: var(--shadow-lg);
  overflow: hidden;
  display: grid;
  grid-template-columns: 1fr 340px;
  position: relative;
}

@media (max-width: 860px) {
  .calc-card {
    grid-template-columns: 1fr;
  }
}

.calc-main-panel {
  padding: 2rem;
}

@media (max-width: 640px) {
  .calc-main-panel {
    padding: 1.25rem;
  }
}

.calc-result-panel {
  background: var(--bg-subtle);
  border-left: 1px solid var(--border-light);
  padding: 2rem;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
}

@media (max-width: 860px) {
  .calc-result-panel {
    border-left: none;
    border-top: 1px solid var(--border-light);
  }
}

/* Rows & Inputs Table */
.calc-table-header {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 40px;
  gap: 0.75rem;
  padding-bottom: 0.6rem;
  border-bottom: 1px solid var(--border-light);
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
  margin-bottom: 0.75rem;
}

.calc-row-item {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 40px;
  gap: 0.75rem;
  align-items: center;
  margin-bottom: 0.6rem;
  animation: fadeIn 0.2s ease-in-out;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(4px); }
  to { opacity: 1; transform: translateY(0); }
}

.calc-input {
  width: 100%;
  padding: 0.65rem 0.85rem;
  font-size: 0.95rem;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  background: var(--bg-surface);
  color: var(--text-main);
  transition: all var(--trans-fast);
}

.calc-input:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: var(--shadow-focus);
}

.calc-row-delete-btn {
  background: transparent;
  border: none;
  color: var(--text-light);
  width: 36px;
  height: 36px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--trans-fast);
}

.calc-row-delete-btn:hover {
  color: var(--danger);
  background: var(--danger-bg);
}

.calc-action-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-top: 1.25rem;
  gap: 0.75rem;
  flex-wrap: wrap;
}

/* Button System */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.65rem 1.25rem;
  font-size: 0.925rem;
  font-weight: 600;
  border-radius: var(--radius-md);
  cursor: pointer;
  border: 1px solid transparent;
  transition: all var(--trans-fast);
  text-decoration: none;
}

.btn-primary {
  background: var(--primary);
  color: white;
}
.btn-primary:hover {
  background: var(--primary-hover);
  box-shadow: 0 4px 12px var(--primary-glow);
}

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

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

/* Result Gauge & Stat Presentation */
.result-header {
  font-size: 0.85rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
  margin-bottom: 1.25rem;
  text-align: center;
}

.gauge-box {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  margin-bottom: 1.5rem;
  position: relative;
}

.score-display {
  font-size: 3.25rem;
  font-weight: 800;
  color: var(--primary);
  line-height: 1;
  letter-spacing: -0.03em;
}

.score-unit {
  font-size: 1.75rem;
  color: var(--text-muted);
}

.letter-badge-large {
  display: inline-block;
  margin-top: 0.5rem;
  font-size: 1.4rem;
  font-weight: 700;
  padding: 0.2rem 1.2rem;
  border-radius: var(--radius-full);
  background: var(--primary-light);
  color: var(--primary);
}

.result-stat-list {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  margin-bottom: 1.5rem;
}

.result-stat-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.9rem;
  padding-bottom: 0.5rem;
  border-bottom: 1px dashed var(--border-light);
}

.result-stat-label {
  color: var(--text-muted);
}

.result-stat-value {
  font-weight: 700;
  color: var(--text-main);
}

/* Badges for Feasibility */
.badge {
  display: inline-flex;
  align-items: center;
  padding: 0.25rem 0.65rem;
  border-radius: var(--radius-full);
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
}
.badge-success { background: var(--success-bg); color: var(--success); }
.badge-warning { background: var(--warning-bg); color: var(--warning); }
.badge-danger { background: var(--danger-bg); color: var(--danger); }
.badge-info { background: var(--info-bg); color: var(--info); }
.badge-highlight { background: var(--primary-light); color: var(--primary); }

/* Formula Breakdown Drawer */
.breakdown-box {
  margin-top: 1.5rem;
  background: var(--bg-surface);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  padding: 1rem;
}

.breakdown-title {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--text-muted);
  text-transform: uppercase;
  margin-bottom: 0.5rem;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.breakdown-content {
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
  font-size: 0.825rem;
  color: var(--text-muted);
  line-height: 1.6;
  white-space: pre-wrap;
  word-break: break-word;
}

/* Content Sections (SEO & Trust Architecture) */
.content-section {
  max-width: 960px;
  margin: 0 auto 3.5rem;
  padding: 0 1.25rem;
}

.section-card {
  background: var(--bg-surface);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-xl);
  padding: 2.5rem;
  box-shadow: var(--shadow-sm);
  margin-bottom: 2rem;
}

@media (max-width: 640px) {
  .section-card {
    padding: 1.5rem;
  }
}

.section-title {
  font-size: 1.75rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--text-main);
  margin-bottom: 1rem;
}

.section-desc {
  font-size: 1.05rem;
  color: var(--text-muted);
  line-height: 1.7;
  margin-bottom: 1.5rem;
}

/* Feature Grid */
.feature-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.5rem;
  margin: 2rem 0;
}

.feature-box {
  background: var(--bg-subtle);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  transition: transform var(--trans-normal);
}

.feature-box:hover {
  transform: translateY(-2px);
  border-color: var(--primary);
}

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

.feature-heading {
  font-size: 1.15rem;
  font-weight: 700;
  margin-bottom: 0.5rem;
}

.feature-text {
  font-size: 0.925rem;
  color: var(--text-muted);
  line-height: 1.6;
}

/* FAQ Accordion */
.faq-list {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.faq-item {
  background: var(--bg-subtle);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  overflow: hidden;
}

.faq-question {
  width: 100%;
  padding: 1.1rem 1.25rem;
  border: none;
  background: transparent;
  color: var(--text-main);
  font-weight: 700;
  font-size: 1rem;
  text-align: left;
  display: flex;
  justify-content: space-between;
  align-items: center;
  cursor: pointer;
}

.faq-question:hover {
  color: var(--primary);
}

.faq-answer {
  padding: 0 1.25rem 1.25rem;
  color: var(--text-muted);
  font-size: 0.95rem;
  line-height: 1.65;
  display: none;
}

.faq-item.active .faq-answer {
  display: block;
}

/* Site Footer */
.site-footer {
  margin-top: auto;
  background: var(--bg-surface);
  border-top: 1px solid var(--border-light);
  padding: 3rem 1.25rem 2rem;
}

.footer-container {
  max-width: 1200px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr;
  gap: 2rem;
  margin-bottom: 2.5rem;
}

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

@media (max-width: 480px) {
  .footer-container {
    grid-template-columns: 1fr;
  }
}

.footer-col-title {
  font-size: 0.85rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-main);
  margin-bottom: 1rem;
}

.footer-link-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.footer-link {
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.9rem;
  transition: color var(--trans-fast);
}

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

.footer-bottom {
  max-width: 1200px;
  margin: 0 auto;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border-light);
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 1rem;
  font-size: 0.85rem;
  color: var(--text-muted);
}