/* ==========================================================================
   Study4Class Pro - Core Stylesheet
   Modern, high-performance academic portal design with rich aesthetics,
   zero bloat, and 100% Core Web Vitals optimization.
   ========================================================================== */

/* ----- Foundational Design Tokens ----- */
:root {
  --school-blue: #2563eb;
  --school-blue-dark: #1d4ed8;
  --school-blue-light: #3b82f6;
  --school-blue-soft: rgba(37, 99, 235, 0.08);
  --school-gold: #c9a227;
  --school-gold-soft: rgba(201, 162, 39, 0.12);
  --school-white: #ffffff;
  --school-gray: #64748b;
  --school-green: #059669;
  --school-green-soft: rgba(5, 150, 105, 0.08);
  --school-red: #dc2626;
  --font: 'Plus Jakarta Sans', 'Source Sans 3', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-display: 'Space Grotesk', var(--font);
  --font-mono: ui-monospace, SFMono-Regular, 'JetBrains Mono', Menlo, Consolas, monospace;
  --bg-page: #faf9ee;
  --grid-line: rgba(34, 139, 34, 0.08);
  --bg-card: #ffffff;
  --bg-card-subtle: #f8f7eb;
  --text-primary: #0f172a;
  --text-muted: #64748b;
  --text-dim: #94a3b8;
  --border-subtle: #e2e8f0;
  --border-strong: #cbd5e1;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.04);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.07), 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, 0.04);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 8px 10px -6px rgba(0, 0, 0, 0.05);
  --radius-sm: 6px;
  --radius: 14px;
  --radius-lg: 18px;
  --radius-full: 9999px;
  --transition-fast: 0.15s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-normal: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}

/* ----- Night Mode Tokens (Tailwind Default Dark Mode) ----- */
html.dark,
body.dark,
body.body-night {
  --bg-page: #0b1120;
  --grid-line: rgba(59, 130, 246, 0.08);
  --bg-card: #1e293b;
  --bg-card-subtle: #0f172a;
  --text-primary: #f8fafc;
  --text-muted: #94a3b8;
  --text-dim: #64748b;
  --border-subtle: #334155;
  --border-strong: #475569;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.35);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.35), 0 2px 4px -2px rgba(0, 0, 0, 0.2);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.4), 0 4px 6px -4px rgba(0, 0, 0, 0.25);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.5);
  --school-white: #1e293b;
  --school-blue-soft: rgba(37, 99, 235, 0.2);
}

/* Tailwind Standard dark: utility mapping */
.dark .dark\:bg-black { background-color: #000000; }
.dark .dark\:bg-gray-950 { background-color: #030712; }
.dark .dark\:bg-gray-900 { background-color: #111827; }
.dark .dark\:bg-gray-800 { background-color: #1f2937; }
.dark .dark\:bg-slate-950 { background-color: #020617; }
.dark .dark\:bg-slate-900 { background-color: #0f172a; }
.dark .dark\:bg-slate-800 { background-color: #1e293b; }
.dark .dark\:bg-slate-700 { background-color: #334155; }

.dark .dark\:text-white { color: #ffffff; }
.dark .dark\:text-gray-50 { color: #f9fafb; }
.dark .dark\:text-gray-100 { color: #f3f4f6; }
.dark .dark\:text-gray-200 { color: #e5e7eb; }
.dark .dark\:text-gray-300 { color: #d1d5db; }
.dark .dark\:text-gray-400 { color: #9ca3af; }
.dark .dark\:text-slate-100 { color: #f1f5f9; }
.dark .dark\:text-slate-200 { color: #e2e8f0; }
.dark .dark\:text-slate-300 { color: #cbd5e1; }
.dark .dark\:text-slate-400 { color: #94a3b8; }

.dark .dark\:border-gray-800 { border-color: #1f2937; }
.dark .dark\:border-gray-700 { border-color: #374151; }
.dark .dark\:border-slate-800 { border-color: #1e293b; }
.dark .dark\:border-slate-700 { border-color: #334155; }

/* ----- Accessibility Utilities ----- */
.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;
}

/* ----- Universal Reset & Base Elements ----- */
*, *::before, *::after {
  box-sizing: border-box;
}

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

body {
  margin: 0;
  padding: 0;
  font-family: var(--font);
  background-color: var(--bg-page);
  background-image:
    linear-gradient(to right, var(--grid-line) 1px, transparent 1px),
    linear-gradient(to bottom, var(--grid-line) 1px, transparent 1px);
  background-size: 28px 28px;
  background-attachment: local;
  color: var(--text-primary);
  min-height: 100vh;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body.body-night {
  background-image:
    linear-gradient(to right, var(--grid-line) 1px, transparent 1px),
    linear-gradient(to bottom, var(--grid-line) 1px, transparent 1px);
  background-size: 28px 28px;
  background-attachment: local;
}

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

a:hover {
  color: var(--school-blue-dark);
  text-decoration: underline;
}

h1, h2, h3, h4, h5, h6 {
  color: var(--text-primary);
  line-height: 1.25;
  letter-spacing: -0.025em;
  font-weight: 700;
}

/* ----- Header Navigation ----- */
.school-header {
  background: var(--bg-card);
  color: var(--text-primary);
  padding: 0.65rem 1.25rem;
  box-shadow: var(--shadow-sm);
  border-bottom: 1px solid var(--border-subtle);
  position: sticky;
  top: 0;
  z-index: 100;
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
}

.header-inner {
  max-width: 1280px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.logo {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  text-decoration: none;
  color: inherit;
  font-weight: 800;
  font-size: 1.2rem;
  letter-spacing: -0.02em;
}

.logo-icon {
  font-size: 1.35rem;
  line-height: 1;
}

.logo-badge {
  font-size: 0.65rem;
  font-weight: 700;
  text-transform: uppercase;
  background: linear-gradient(135deg, var(--school-blue), #1d4ed8);
  color: #ffffff;
  padding: 0.15rem 0.45rem;
  border-radius: var(--radius-full);
  letter-spacing: 0.05em;
  margin-left: 0.15rem;
}

.main-nav {
  display: flex;
  align-items: center;
  gap: 0.45rem;
  flex-wrap: wrap;
}

.main-nav a {
  color: #334155;
  font-weight: 600;
  font-size: 0.85rem;
  padding: 0.35rem 0.85rem;
  border-radius: 8px;
  border: 1px solid var(--border-subtle);
  background: var(--bg-card);
  text-decoration: none;
  transition: all var(--transition-fast);
}

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

body.body-night .main-nav a {
  background: #1e293b;
  border-color: #334155;
  color: #cbd5e1;
}

body.body-night .main-nav a:hover {
  background: #334155;
  color: #ffffff;
}

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

.nav-break-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  background: rgba(124, 92, 255, 0.1);
  color: #7c5cff;
  border: 1px solid rgba(124, 92, 255, 0.25);
  font-family: var(--font);
  font-size: 0.825rem;
  font-weight: 600;
  padding: 0.35rem 0.8rem;
  border-radius: 8px;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.nav-break-btn:hover {
  background: #7c5cff;
  color: #ffffff;
  border-color: #7c5cff;
  transform: translateY(-1px);
}

.theme-toggle {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  font-size: 0.95rem;
  padding: 0.35rem 0.65rem;
  cursor: pointer;
  border-radius: 8px;
  line-height: 1;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition-fast);
}

.theme-toggle:hover {
  background: var(--border-subtle);
}

body.body-night .theme-toggle {
  background: #1e293b;
  border-color: #334155;
}

/* ----- Main Content Wrapper ----- */
.school-main {
  max-width: 1280px;
  margin: 0 auto;
  padding: 2rem 1.25rem 4rem;
}

/* ----- Hero Section (Modern Elevated Portal Banner) ----- */
.hero-section {
  padding: 1.5rem 0 2rem;
  margin-bottom: 0.5rem;
}

.hero-card {
  position: relative;
  background: linear-gradient(135deg, rgba(255, 255, 255, 0.98) 0%, rgba(248, 250, 252, 0.95) 100%);
  border: 1px solid rgba(226, 232, 240, 0.9);
  border-radius: var(--radius-lg);
  padding: 2rem 2.25rem;
  box-shadow: 0 10px 30px -10px rgba(15, 23, 42, 0.05), 0 1px 3px rgba(0, 0, 0, 0.02);
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 1.5rem 2.5rem;
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
}

body.body-night .hero-card {
  background: linear-gradient(135deg, rgba(30, 41, 59, 0.95) 0%, rgba(15, 23, 42, 0.9) 100%);
  border-color: #334155;
  box-shadow: 0 10px 30px -10px rgba(0, 0, 0, 0.4);
}

.hero-card-left {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 0.75rem;
}

.hero-pill {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  background: rgba(37, 99, 235, 0.08);
  color: var(--school-blue);
  font-size: 0.8rem;
  font-weight: 700;
  padding: 0.35rem 0.85rem;
  border-radius: var(--radius-full);
  border: 1px solid rgba(37, 99, 235, 0.18);
  letter-spacing: 0.02em;
}

.hero-pill-dot {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--school-green);
  box-shadow: 0 0 0 2px rgba(5, 150, 105, 0.2);
  display: inline-block;
}

body.body-night .hero-pill {
  background: rgba(37, 99, 235, 0.18);
  color: #93c5fd;
  border-color: rgba(59, 130, 246, 0.3);
}

.hero-title {
  font-family: var(--font-display);
  font-size: 2.5rem;
  font-weight: 800;
  letter-spacing: -0.035em;
  margin: 0;
  color: var(--text-primary);
  line-height: 1.15;
}

.hero-title-accent {
  background: linear-gradient(135deg, #2563eb 0%, #7c5cff 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-card-right {
  flex: 1;
  min-width: 280px;
  max-width: 580px;
}

.hero-tagline {
  font-size: 1rem;
  color: var(--text-muted);
  margin: 0 0 0.85rem 0;
  line-height: 1.55;
}

.hero-features {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.hero-chip {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--text-muted);
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  padding: 0.25rem 0.65rem;
  border-radius: 6px;
}

body.body-night .hero-chip {
  background: rgba(15, 23, 42, 0.6);
  border-color: #334155;
}

/* ----- Tools Section & Search Controls ----- */
.tools-section {
  margin-bottom: 3.5rem;
}

.tools-header-block {
  margin-bottom: 1.25rem;
}

.tools-section-kicker {
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: 0.65rem;
}

.tools-search-box {
  position: relative;
  width: 100%;
  max-width: 440px;
  margin-bottom: 0.4rem;
}

.tools-search-input {
  width: 100%;
  padding: 0.65rem 1rem 0.65rem 2.4rem;
  font-size: 0.95rem;
  font-family: var(--font);
  background: #ffffff;
  color: var(--text-primary);
  border: 1px solid #cbd5e1;
  border-radius: 8px;
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.04);
  outline: none;
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

body.body-night .tools-search-input {
  background: #1e293b;
  border-color: #334155;
  color: #f8fafc;
}

.tools-search-input:focus {
  border-color: var(--school-blue);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.15);
}

.tools-search-icon {
  position: absolute;
  left: 0.85rem;
  top: 50%;
  transform: translateY(-50%);
  font-size: 0.95rem;
  color: var(--text-dim);
  pointer-events: none;
}

.tools-pin-hint {
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-bottom: 1rem;
}

.tools-filter-pills {
  display: flex;
  gap: 0.4rem;
  flex-wrap: wrap;
  margin-bottom: 1.25rem;
}

.filter-pill {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  color: var(--text-muted);
  font-size: 0.825rem;
  font-weight: 600;
  padding: 0.35rem 0.75rem;
  border-radius: var(--radius-full);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.filter-pill:hover, .filter-pill.active {
  background: var(--school-blue);
  color: #ffffff;
  border-color: var(--school-blue);
}

/* ----- Tools Grid & Cards (Colorful Pastel Tints matching study4class.com) ----- */
.tools-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(210px, 1fr));
  gap: 1.25rem;
}

.tool-card {
  background: #ffffff;
  border: 1px solid rgba(0, 0, 0, 0.08);
  border-radius: var(--radius);
  padding: 1.35rem 1.25rem 1.25rem;
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  text-align: left;
  color: inherit;
  transition: transform var(--transition-normal), box-shadow var(--transition-normal), border-color var(--transition-normal);
  cursor: pointer;
  position: relative;
  user-select: none;
  width: 100%;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.04);
}

/* Authentic colorful pastel card backgrounds */
.tool-card[data-tool="calculator"] { background: #fefce8; border-color: #fef08a; }
.tool-card[data-tool="timer"] { background: #f0f7ff; border-color: #bfdbfe; }
.tool-card[data-tool="pomodoro"] { background: #fff1f2; border-color: #fecdd3; }
.tool-card[data-tool="wordcounter"] { background: #f5f3ff; border-color: #ddd6fe; }
.tool-card[data-tool="gpa"] { background: #f0fdf4; border-color: #bbf7d0; }
.tool-card[data-tool="notes"] { background: #fef9c3; border-color: #fef08a; }
.tool-card[data-tool="converter"] { background: #eff6ff; border-color: #bfdbfe; }
.tool-card[data-tool="formulas"] { background: #eef2ff; border-color: #c7d2fe; }
.tool-card[data-tool="citations"] { background: #faf5ff; border-color: #e9d5ff; }
.tool-card[data-tool="finalgrade"] { background: #ecfdf5; border-color: #a7f3d0; }
.tool-card[data-tool="practice"] { background: #fff7ed; border-color: #fed7aa; }
.tool-card[data-tool="typing"] { background: #f0f9ff; border-color: #bae6fd; }
.tool-card[data-tool="cornell"] { background: #fefce8; border-color: #fef08a; }
.tool-card[data-tool="quadratic"] { background: #f5f3ff; border-color: #ddd6fe; }
.tool-card[data-tool="percentage"] { background: #ffe4e6; border-color: #fecdd3; }
.tool-card[data-tool="fraction"] { background: #f7fee7; border-color: #d9f99d; }

.tool-card:hover {
  box-shadow: 0 10px 22px -3px rgba(0, 0, 0, 0.08), 0 3px 6px -1px rgba(0, 0, 0, 0.03);
  transform: translateY(-4px);
}

/* Night Mode Colorful Card Accents */
body.body-night .tool-card {
  background: #1e293b !important;
  border-color: #334155;
  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.35);
}

body.body-night .tool-card[data-tool="calculator"] { border-color: rgba(234, 179, 8, 0.45); }
body.body-night .tool-card[data-tool="timer"] { border-color: rgba(59, 130, 246, 0.45); }
body.body-night .tool-card[data-tool="pomodoro"] { border-color: rgba(244, 63, 94, 0.45); }
body.body-night .tool-card[data-tool="wordcounter"] { border-color: rgba(168, 85, 247, 0.45); }
body.body-night .tool-card[data-tool="gpa"] { border-color: rgba(34, 197, 94, 0.45); }
body.body-night .tool-card[data-tool="notes"] { border-color: rgba(234, 179, 8, 0.45); }
body.body-night .tool-card[data-tool="converter"] { border-color: rgba(59, 130, 246, 0.45); }
body.body-night .tool-card[data-tool="formulas"] { border-color: rgba(99, 102, 241, 0.45); }
body.body-night .tool-card[data-tool="citations"] { border-color: rgba(168, 85, 247, 0.45); }
body.body-night .tool-card[data-tool="finalgrade"] { border-color: rgba(16, 185, 129, 0.45); }
body.body-night .tool-card[data-tool="practice"] { border-color: rgba(249, 115, 22, 0.45); }
body.body-night .tool-card[data-tool="typing"] { border-color: rgba(14, 165, 233, 0.45); }
body.body-night .tool-card[data-tool="cornell"] { border-color: rgba(234, 179, 8, 0.45); }
body.body-night .tool-card[data-tool="quadratic"] { border-color: rgba(99, 102, 241, 0.45); }
body.body-night .tool-card[data-tool="percentage"] { border-color: rgba(244, 63, 94, 0.45); }
body.body-night .tool-card[data-tool="fraction"] { border-color: rgba(132, 204, 22, 0.45); }

.tool-card:focus-visible {
  outline: 2px solid var(--school-blue);
  outline-offset: 2px;
}

.tool-card.pinned {
  border-width: 2px;
  border-color: var(--school-gold) !important;
}

.tool-pin-btn {
  position: absolute;
  top: 0.75rem;
  right: 0.75rem;
  width: 28px;
  height: 28px;
  border: 1px solid rgba(0, 0, 0, 0.08);
  background: #ffffff;
  color: #94a3b8;
  font-size: 1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  line-height: 1;
  border-radius: 50%;
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.04);
  transition: color var(--transition-fast), transform var(--transition-fast), border-color var(--transition-fast);
}

.tool-pin-btn:hover {
  color: #eab308;
  border-color: #fef08a;
  transform: scale(1.15);
}

.tool-pin-btn.is-pinned {
  color: #eab308;
  border-color: #fef08a;
}

body.body-night .tool-pin-btn {
  background: #0f172a;
  border-color: #334155;
  color: #64748b;
}

.svg-icon {
  display: inline-block;
  vertical-align: middle;
  width: 1.15rem;
  height: 1.15rem;
  stroke: currentColor;
  stroke-width: 2;
  fill: none;
  stroke-linecap: round;
  stroke-linejoin: round;
  flex-shrink: 0;
}

/* Dashed Icon Container Box matching study4class.com */
.tool-icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 48px;
  height: 48px;
  border-radius: 12px;
  border: 1.5px dashed #cbd5e1;
  background: #ffffff;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.03);
  transition: transform var(--transition-fast), border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.tool-card:hover .tool-icon {
  transform: scale(1.08);
  border-color: rgba(0, 0, 0, 0.3);
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.06);
}

body.body-night .tool-icon {
  background: #0f172a;
  border-color: #475569;
}

/* Card-specific vibrant icon strokes */
.tool-icon svg {
  width: 1.65rem;
  height: 1.65rem;
  fill: none;
  stroke-width: 2;
  stroke-linecap: round;
  stroke-linejoin: round;
  transition: transform var(--transition-fast);
}

.tool-card[data-tool="calculator"] .tool-icon svg { stroke: #2563eb; }
.tool-card[data-tool="timer"] .tool-icon svg { stroke: #0284c7; }
.tool-card[data-tool="pomodoro"] .tool-icon svg { stroke: #e11d48; }
.tool-card[data-tool="wordcounter"] .tool-icon svg { stroke: #7c3aed; }
.tool-card[data-tool="gpa"] .tool-icon svg { stroke: #059669; }
.tool-card[data-tool="notes"] .tool-icon svg { stroke: #d97706; }
.tool-card[data-tool="converter"] .tool-icon svg { stroke: #2563eb; }
.tool-card[data-tool="formulas"] .tool-icon svg { stroke: #4f46e5; }
.tool-card[data-tool="citations"] .tool-icon svg { stroke: #9333ea; }
.tool-card[data-tool="finalgrade"] .tool-icon svg { stroke: #059669; }
.tool-card[data-tool="practice"] .tool-icon svg { stroke: #ea580c; }
.tool-card[data-tool="typing"] .tool-icon svg { stroke: #0284c7; }
.tool-card[data-tool="cornell"] .tool-icon svg { stroke: #ca8a04; }
.tool-card[data-tool="quadratic"] .tool-icon svg { stroke: #6366f1; }
.tool-card[data-tool="percentage"] .tool-icon svg { stroke: #f43f5e; }
.tool-card[data-tool="fraction"] .tool-icon svg { stroke: #65a30d; }

body.body-night .tool-card .tool-icon svg {
  stroke: #93c5fd;
}
body.body-night .tool-card[data-tool="pomodoro"] .tool-icon svg { stroke: #fda4af; }
body.body-night .tool-card[data-tool="wordcounter"] .tool-icon svg { stroke: #d8b4fe; }
body.body-night .tool-card[data-tool="gpa"] .tool-icon svg { stroke: #86efac; }
body.body-night .tool-card[data-tool="notes"] .tool-icon svg { stroke: #fde047; }
body.body-night .tool-card[data-tool="practice"] .tool-icon svg { stroke: #fdba74; }

.logo-icon svg {
  width: 1.4rem;
  height: 1.4rem;
  stroke: var(--school-blue);
  fill: none;
  stroke-width: 2.2;
  vertical-align: middle;
}

.footer-brand svg {
  width: 1.4rem;
  height: 1.4rem;
  stroke: var(--school-blue);
  fill: none;
  stroke-width: 2.2;
  vertical-align: middle;
}

.theme-toggle svg {
  width: 1.15rem;
  height: 1.15rem;
  stroke: currentColor;
  fill: none;
  stroke-width: 2;
  display: block;
}

.tool-card:hover .tool-icon {
  transform: scale(1.08);
}

.tool-label {
  font-weight: 700;
  font-size: 1rem;
  color: var(--text-primary);
  margin-top: 0.25rem;
}

.tool-desc {
  font-size: 0.8rem;
  color: var(--text-muted);
  line-height: 1.35;
}

.tools-empty-state {
  text-align: center;
  padding: 3rem 1rem;
  color: var(--text-muted);
  grid-column: 1 / -1;
  background: var(--bg-card);
  border: 1px dashed var(--border-subtle);
  border-radius: var(--radius);
}

/* ==========================================================================
   Comprehensive Academic Guidebook (~10,000 Words) Layout
   ========================================================================== */
.guidebook-section {
  margin-top: 4rem;
  padding-top: 2rem;
  border-top: 2px solid var(--border-subtle);
}

.guidebook-hero {
  margin-bottom: 2.5rem;
}

.guidebook-hero-title {
  font-size: clamp(1.75rem, 3.5vw, 2.4rem);
  font-weight: 800;
  letter-spacing: -0.03em;
  margin: 0 0 0.75rem;
}

.guidebook-hero-desc {
  font-size: 1.05rem;
  color: var(--text-muted);
  max-width: 860px;
  line-height: 1.6;
  margin: 0;
}

/* 2-Column Responsive Layout: Sticky TOC + Main Article */
.guidebook-layout {
  display: grid;
  grid-template-columns: 280px 1fr;
  gap: 2.5rem;
  align-items: start;
}

@media (max-width: 1024px) {
  .guidebook-layout {
    grid-template-columns: 1fr;
    gap: 2rem;
  }
}

/* Table of Contents Sticky Sidebar */
.toc-sidebar {
  position: sticky;
  top: 5rem;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 1.25rem;
  box-shadow: var(--shadow-sm);
  max-height: calc(100vh - 6.5rem);
  overflow-y: auto;
}

.toc-title {
  font-size: 0.825rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  margin: 0 0 0.85rem;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.toc-list {
  list-style: none;
  padding: 0;
  margin: 0;
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}

.toc-link {
  display: block;
  font-size: 0.85rem;
  font-weight: 500;
  color: var(--text-muted);
  padding: 0.35rem 0.65rem;
  border-radius: var(--radius-sm);
  text-decoration: none;
  line-height: 1.35;
  transition: all var(--transition-fast);
}

.toc-link:hover {
  background: var(--school-blue-soft);
  color: var(--school-blue);
  text-decoration: none;
}

.toc-link.active {
  background: var(--school-blue);
  color: #ffffff;
  font-weight: 600;
}

/* Main Article Chapters */
.guidebook-content {
  min-width: 0;
}

.guide-chapter {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 2.5rem 2.25rem;
  margin-bottom: 2.5rem;
  box-shadow: var(--shadow-sm);
  scroll-margin-top: 5.5rem;
}

.chapter-badge {
  display: inline-block;
  font-size: 0.725rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--school-blue);
  background: var(--school-blue-soft);
  padding: 0.2rem 0.6rem;
  border-radius: var(--radius-full);
  margin-bottom: 0.75rem;
}

.guide-chapter h2 {
  font-size: clamp(1.4rem, 2.5vw, 1.85rem);
  font-weight: 800;
  margin: 0 0 1.25rem;
  line-height: 1.3;
}

.guide-chapter h3 {
  font-size: 1.2rem;
  font-weight: 700;
  margin: 1.75rem 0 0.75rem;
  color: var(--text-primary);
}

.guide-chapter h4 {
  font-size: 1.025rem;
  font-weight: 600;
  margin: 1.25rem 0 0.5rem;
}

.guide-chapter p {
  color: var(--text-primary);
  font-size: 1rem;
  line-height: 1.75;
  margin: 0 0 1.25rem;
}

/* Answer-First (BLUF) Box per Claude-SEO Standards */
.bluf-box {
  background: var(--school-blue-soft);
  border-left: 4px solid var(--school-blue);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 1.15rem 1.35rem;
  margin: 1.25rem 0 1.75rem;
}

.bluf-label {
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--school-blue);
  margin-bottom: 0.35rem;
  display: flex;
  align-items: center;
  gap: 0.35rem;
}

.bluf-text {
  font-size: 1.025rem;
  font-weight: 600;
  color: var(--text-primary);
  line-height: 1.55;
  margin: 0;
}

/* Key Takeaways Box per Claude-Blog Standards */
.takeaways-box {
  background: var(--school-green-soft);
  border: 1px solid rgba(5, 150, 105, 0.25);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  margin: 1.75rem 0;
}

.takeaways-title {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--school-green);
  margin: 0 0 0.65rem;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.takeaways-list {
  margin: 0;
  padding-left: 1.25rem;
  color: var(--text-primary);
  font-size: 0.95rem;
  line-height: 1.6;
}

.takeaways-list li {
  margin-bottom: 0.45rem;
}

/* Worked Example & Practical Application Cards */
.example-box {
  background: var(--bg-page);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius);
  padding: 1.35rem 1.5rem;
  margin: 1.5rem 0;
}

.example-title {
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--school-blue-dark);
  margin: 0 0 0.5rem;
  display: flex;
  align-items: center;
  gap: 0.35rem;
}

/* Data Tables */
.data-table-wrap {
  width: 100%;
  overflow-x: auto;
  margin: 1.5rem 0;
  border-radius: var(--radius);
  border: 1px solid var(--border-subtle);
  box-shadow: var(--shadow-sm);
}

.data-table {
  width: 100%;
  border-collapse: collapse;
  text-align: left;
  font-size: 0.925rem;
  background: var(--bg-card);
}

.data-table th {
  background: var(--bg-card-subtle);
  color: var(--text-primary);
  font-weight: 700;
  padding: 0.85rem 1rem;
  border-bottom: 2px solid var(--border-subtle);
  white-space: nowrap;
}

.data-table td {
  padding: 0.8rem 1rem;
  border-bottom: 1px solid var(--border-subtle);
  color: var(--text-primary);
}

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

.data-table tr:hover td {
  background: var(--school-blue-soft);
}

/* Formula Presentation Blocks */
.formula-block {
  font-family: var(--font-mono);
  background: var(--bg-card-subtle);
  border: 1px solid var(--border-subtle);
  padding: 0.85rem 1.25rem;
  border-radius: var(--radius-sm);
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--school-blue);
  display: block;
  overflow-x: auto;
  margin: 1rem 0;
}

/* Contextual Tool Callout */
.tool-callout {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.75rem;
  background: linear-gradient(135deg, rgba(37, 99, 235, 0.05), rgba(201, 162, 39, 0.05));
  border: 1px dashed var(--school-blue);
  border-radius: var(--radius);
  padding: 1rem 1.25rem;
  margin: 1.5rem 0;
}

.tool-callout-text {
  font-size: 0.925rem;
  font-weight: 600;
  color: var(--text-primary);
  margin: 0;
}

.tool-callout-btn,
a.tool-callout-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  background: var(--school-blue);
  color: #ffffff !important;
  font-size: 0.825rem;
  font-weight: 700;
  padding: 0.45rem 0.85rem;
  border-radius: var(--radius-full);
  text-decoration: none !important;
  transition: all var(--transition-fast);
}

.tool-callout-btn:hover,
a.tool-callout-btn:hover {
  background: var(--school-blue-dark);
  color: #ffffff !important;
  text-decoration: none !important;
  transform: translateY(-1px);
}

/* ==========================================================================
   Universal Tool Modal Dialogs
   ========================================================================== */
.tool-modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(15, 23, 42, 0.75);
  backdrop-filter: blur(6px);
  -webkit-backdrop-filter: blur(6px);
  z-index: 1000;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1rem;
  opacity: 0;
  pointer-events: none;
  transition: opacity var(--transition-normal);
}

.tool-modal-overlay.active {
  opacity: 1;
  pointer-events: auto;
}

.tool-modal-panel {
  background: var(--bg-card);
  color: var(--text-primary);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-subtle);
  box-shadow: var(--shadow-xl);
  width: 100%;
  max-width: 680px;
  max-height: 90vh;
  display: flex;
  flex-direction: column;
  transform: translateY(12px) scale(0.98);
  transition: transform var(--transition-normal);
  overflow: hidden;
}

.tool-modal-overlay.active .tool-modal-panel {
  transform: translateY(0) scale(1);
}

.tool-modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1.15rem 1.5rem;
  border-bottom: 1px solid var(--border-subtle);
  background: var(--bg-card);
}

.tool-modal-title-wrap {
  display: flex;
  align-items: center;
  gap: 0.65rem;
}

.tool-modal-icon {
  font-size: 1.5rem;
}

.tool-modal-title {
  margin: 0;
  font-size: 1.25rem;
  font-weight: 700;
}

.tool-modal-close {
  background: var(--bg-card-subtle);
  border: 1px solid var(--border-subtle);
  color: var(--text-muted);
  width: 2rem;
  height: 2rem;
  border-radius: var(--radius-full);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.25rem;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.tool-modal-close:hover {
  background: var(--border-strong);
  color: var(--text-primary);
}

.tool-modal-body {
  padding: 1.5rem;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  gap: 1.15rem;
}

/* Tool Interactive Elements */
.tool-input-group {
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
}

.tool-label-text {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-primary);
}

.tool-input, .tool-select, .tool-textarea {
  width: 100%;
  padding: 0.65rem 0.85rem;
  font-family: var(--font);
  font-size: 0.95rem;
  background: var(--bg-page);
  color: var(--text-primary);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  outline: none;
  transition: border-color var(--transition-fast);
}

.tool-input:focus, .tool-select:focus, .tool-textarea:focus {
  border-color: var(--school-blue);
  background: var(--bg-card);
}

.tool-btn,
a.tool-btn,
button.tool-btn {
  background: var(--school-blue);
  color: #ffffff !important;
  border: none;
  font-family: var(--font);
  font-size: 0.95rem;
  font-weight: 600;
  padding: 0.65rem 1.25rem;
  border-radius: var(--radius-sm);
  cursor: pointer;
  text-decoration: none !important;
  transition: background var(--transition-fast), transform var(--transition-fast), color var(--transition-fast);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.35rem;
}

.tool-btn:hover,
a.tool-btn:hover,
button.tool-btn:hover {
  background: var(--school-blue-dark);
  color: #ffffff !important;
  text-decoration: none !important;
}

.tool-btn:active,
a.tool-btn:active,
button.tool-btn:active {
  transform: translateY(1px);
  color: #ffffff !important;
}

.tool-btn-secondary,
a.tool-btn-secondary,
button.tool-btn-secondary {
  background: var(--bg-card-subtle);
  color: var(--text-primary) !important;
  border: 1px solid var(--border-subtle);
  text-decoration: none !important;
}

.tool-btn-secondary:hover,
a.tool-btn-secondary:hover,
button.tool-btn-secondary:hover {
  background: var(--border-subtle);
  color: var(--text-primary) !important;
  text-decoration: none !important;
}

.tool-output-card {
  background: var(--bg-page);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius);
  padding: 1.15rem;
  text-align: center;
}

.tool-output-val {
  font-size: 1.85rem;
  font-weight: 800;
  color: var(--school-blue);
  font-family: var(--font-mono);
}

.tool-output-meta {
  font-size: 0.825rem;
  color: var(--text-muted);
}

/* Calculator Grid */
.calc-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.45rem;
}

.calc-display {
  grid-column: 1 / -1;
  background: #1e293b;
  color: #38bdf8;
  font-family: var(--font-mono);
  font-size: 1.6rem;
  padding: 0.85rem 1rem;
  border-radius: var(--radius-sm);
  text-align: right;
  overflow-x: auto;
  border: 2px solid #0f172a;
}

.calc-btn {
  font-family: var(--font-mono);
  font-size: 1.05rem;
  font-weight: 700;
  padding: 0.75rem 0.5rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-subtle);
  background: var(--bg-card);
  color: var(--text-primary);
  cursor: pointer;
  transition: all 0.1s ease;
}

.calc-btn:hover {
  background: var(--bg-card-subtle);
}

.calc-btn:active {
  transform: translateY(1.5px);
}

.calc-btn-op {
  background: var(--school-blue-soft);
  color: var(--school-blue);
}

.calc-btn-eq {
  background: var(--school-blue);
  color: #ffffff;
}

.calc-btn-clear {
  background: rgba(220, 38, 38, 0.1);
  color: var(--school-red);
}

/* ==========================================================================
   FAQ Section
   ========================================================================== */
.faq-section {
  margin-top: 3.5rem;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 2.5rem 2rem;
  box-shadow: var(--shadow-sm);
}

.faq-title {
  font-size: 1.5rem;
  font-weight: 800;
  margin: 0 0 1.5rem;
}

.faq-grid {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.faq-item {
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius);
  overflow: hidden;
  transition: border-color var(--transition-fast);
}

.faq-question {
  width: 100%;
  text-align: left;
  background: var(--bg-card);
  padding: 1.15rem 1.25rem;
  font-size: 1.025rem;
  font-weight: 700;
  color: var(--text-primary);
  border: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  font-family: var(--font);
}

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

.faq-arrow {
  font-size: 0.85rem;
  transition: transform var(--transition-fast);
}

.faq-item.active .faq-arrow {
  transform: rotate(180deg);
}

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

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

/* ==========================================================================
   Footer
   ========================================================================== */
.school-footer {
  margin-top: 5rem;
  padding: 3rem 1.25rem 2.5rem;
  background: var(--bg-card);
  border-top: 1px solid var(--border-subtle);
  color: var(--text-muted);
  font-size: 0.9rem;
  text-align: center;
}

.footer-inner {
  max-width: 1280px;
  margin: 0 auto;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1.25rem;
}

.footer-brand {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-weight: 700;
  color: var(--text-primary);
  font-size: 1.05rem;
}

.footer-links {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  gap: 0.5rem 1rem;
}

.footer-links a {
  color: var(--text-muted);
  font-weight: 500;
  text-decoration: none;
}

.footer-links a:hover {
  color: var(--school-blue);
  text-decoration: underline;
}

.footer-sep {
  color: var(--border-strong);
}

.footer-disclaimer {
  font-size: 0.8rem;
  color: var(--text-dim);
  max-width: 720px;
  line-height: 1.5;
  margin: 0;
}

/* ==========================================================================
   iOS Squircle Scientific Calculator Chassis
   ========================================================================== */
.ios-calc-chassis {
  background-color: #24262b !important;
  border: 1px solid #363942 !important;
  border-radius: 28px !important;
  width: 100% !important;
  max-width: 350px !important;
  padding: 16px !important;
  box-shadow: 0 25px 60px -10px rgba(0, 0, 0, 0.95), 0 0 0 1px rgba(255, 255, 255, 0.05) !important;
  display: flex !important;
  flex-direction: column !important;
  gap: 12px !important;
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Display", "Segoe UI", Roboto, sans-serif !important;
  position: relative !important;
  z-index: 10 !important;
}

.ios-calc-header {
  display: flex !important;
  align-items: center !important;
  justify-content: space-between !important;
  padding-bottom: 6px !important;
  border-bottom: 1px solid rgba(255, 255, 255, 0.08) !important;
}

.ios-calc-screen {
  background-color: #121316 !important;
  border: 1px solid #282a30 !important;
  border-radius: 18px !important;
  padding: 12px 16px !important;
  text-align: right !important;
  min-height: 80px !important;
  display: flex !important;
  flex-direction: column !important;
  justify-content: space-between !important;
  overflow: hidden !important;
}

.ios-calc-subdisplay {
  font-size: 11px !important;
  color: #9ca3af !important;
  font-family: monospace !important;
  font-weight: 600 !important;
  letter-spacing: 0.05em !important;
}

.ios-calc-display {
  font-size: 36px !important;
  font-weight: 700 !important;
  color: #ffffff !important;
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Display", monospace !important;
  line-height: 1.1 !important;
  overflow: hidden !important;
  text-overflow: ellipsis !important;
  white-space: nowrap !important;
}

.ios-calc-grid {
  display: grid !important;
  grid-template-columns: repeat(4, 1fr) !important;
  gap: 8px !important;
}

.ios-calc-btn {
  border: none !important;
  outline: none !important;
  border-radius: 18px !important;
  cursor: pointer !important;
  user-select: none !important;
  display: flex !important;
  align-items: center !important;
  justify-content: center !important;
  transition: transform 0.08s ease, filter 0.12s ease, background-color 0.12s ease !important;
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Display", "Segoe UI", Roboto, sans-serif !important;
  padding: 0 !important;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.25) !important;
}

.ios-calc-btn:active {
  transform: scale(0.93) !important;
  filter: brightness(1.2) !important;
}

/* Primary Top Function Keys (C, ±, %) */
.ios-calc-btn-top {
  background-color: #555961 !important;
  color: #ffffff !important;
  font-size: 23px !important;
  font-weight: 600 !important;
  height: 56px !important;
}
.ios-calc-btn-top:hover {
  background-color: #636772 !important;
}

/* Right Operator Column (÷, ×, -, +, =) */
.ios-calc-btn-op {
  background-color: #ff9f0a !important;
  color: #ffffff !important;
  font-size: 27px !important;
  font-weight: 700 !important;
  height: 56px !important;
}
.ios-calc-btn-op:hover {
  background-color: #f09300 !important;
}

/* Number Digits (7, 8, 9, 4, 5, 6, 1, 2, 3, 0, .) */
.ios-calc-btn-num {
  background-color: #3b3e45 !important;
  color: #ffffff !important;
  font-size: 25px !important;
  font-weight: 600 !important;
  height: 56px !important;
}
.ios-calc-btn-num:hover {
  background-color: #474b54 !important;
}
.ios-calc-btn-zero {
  grid-column: span 2 !important;
  border-radius: 20px !important;
}

/* Scientific Function Keys (sin, cos, tan, √, x², log, ln, π, e, (, ), ⌫) */
.ios-calc-btn-sci {
  background-color: #2b2e34 !important;
  color: #38bdf8 !important;
  font-size: 15px !important;
  font-weight: 600 !important;
  height: 42px !important;
  border-radius: 14px !important;
}
.ios-calc-btn-sci:hover {
  background-color: #363a42 !important;
  color: #70e0ff !important;
}
.ios-calc-btn-del {
  color: #fbbf24 !important;
  font-size: 17px !important;
}