/* ============================================================
   MathSpace - Clean, Minimalist & Responsive Design System
   ============================================================ */

:root {
  /* Color Palette - Light Mode (Clean, academic, minimalist) */
  --bg-primary: #ffffff;
  --bg-secondary: #f8fafc;
  --bg-tertiary: #f1f5f9;
  --bg-card: #ffffff;
  --bg-accent-subtle: #eff6ff;
  
  --border-color: #e2e8f0;
  --border-hover: #cbd5e1;
  --border-focus: #3b82f6;

  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #94a3b8;
  
  /* Single Primary Accent */
  --accent: #2563eb;
  --accent-hover: #1d4ed8;
  --accent-text: #ffffff;
  --accent-light: #dbeafe;
  --accent-ring: rgba(37, 99, 235, 0.2);

  /* Functional Colors */
  --danger: #ef4444;
  --danger-bg: #fef2f2;
  --danger-border: #fecaca;
  --success: #10b981;
  --success-bg: #ecfdf5;

  /* Elevation / 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);

  /* Radii */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;
  --radius-full: 9999px;

  /* Typography */
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  --font-mono: 'SFMono-Regular', Consolas, "Liberation Mono", Menlo, Courier, monospace;
}

[data-theme="dark"] {
  --bg-primary: #0b0f19;
  --bg-secondary: #111827;
  --bg-tertiary: #1f2937;
  --bg-card: #111827;
  --bg-accent-subtle: #172554;

  --border-color: #1f2937;
  --border-hover: #374151;
  --border-focus: #3b82f6;

  --text-primary: #f8fafc;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;

  --accent: #3b82f6;
  --accent-hover: #60a5fa;
  --accent-text: #ffffff;
  --accent-light: #1e3a8a;
  --accent-ring: rgba(59, 130, 246, 0.3);

  --danger-bg: #450a0a;
  --danger-border: #7f1d1d;
  --success-bg: #064e3b;

  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.4);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.5);
}

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-sans);
  background-color: var(--bg-secondary);
  color: var(--text-primary);
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* Header & Navigation */
.header {
  background-color: var(--bg-primary);
  border-bottom: 1px solid var(--border-color);
  position: sticky;
  top: 0;
  z-index: 50;
}

.header-container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0.85rem 1.25rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}

.logo-group {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  text-decoration: none;
  color: inherit;
  cursor: pointer;
}

.logo-icon {
  width: 34px;
  height: 34px;
  background-color: var(--accent);
  color: #fff;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 1.1rem;
  user-select: none;
}

.logo-text {
  display: flex;
  flex-direction: column;
}

.logo-title {
  font-size: 1.25rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--text-primary);
}

.logo-tagline {
  font-size: 0.75rem;
  color: var(--text-secondary);
  letter-spacing: 0.01em;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

.pi-selector-wrap {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  background-color: var(--bg-tertiary);
  border: 1px solid var(--border-color);
  padding: 0.3rem 0.6rem;
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  color: var(--text-secondary);
}

.pi-select {
  border: none;
  background: transparent;
  font-family: inherit;
  font-size: 0.85rem;
  color: var(--text-primary);
  font-weight: 600;
  cursor: pointer;
  outline: none;
}

.icon-btn {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  border-radius: var(--radius-sm);
  padding: 0.45rem 0.75rem;
  font-size: 0.85rem;
  font-family: inherit;
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  cursor: pointer;
  transition: background-color 0.15s, border-color 0.15s, color 0.15s;
}

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

.icon-btn.primary-btn {
  background-color: var(--accent);
  color: var(--accent-text);
  border-color: var(--accent);
  font-weight: 600;
}

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

/* Main Content Area */
.main-wrapper {
  flex: 1;
  max-width: 1200px;
  width: 100%;
  margin: 0 auto;
  padding: 1.75rem 1.25rem 3rem 1.25rem;
}

/* Search and Filters */
.dashboard-controls {
  margin-bottom: 2rem;
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

.search-box {
  position: relative;
  max-width: 640px;
  width: 100%;
  margin: 0 auto;
}

.search-input {
  width: 100%;
  padding: 0.85rem 1rem 0.85rem 2.8rem;
  font-size: 1rem;
  font-family: inherit;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  box-shadow: var(--shadow-sm);
  outline: none;
  transition: border-color 0.15s, box-shadow 0.15s;
}

.search-input:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-ring);
}

.search-icon {
  position: absolute;
  left: 1rem;
  top: 50%;
  transform: translateY(-50%);
  color: var(--text-muted);
  pointer-events: none;
  display: flex;
}

.search-clear-btn {
  position: absolute;
  right: 0.85rem;
  top: 50%;
  transform: translateY(-50%);
  background: none;
  border: none;
  color: var(--text-muted);
  cursor: pointer;
  padding: 0.25rem;
  font-size: 1.1rem;
  display: none;
}

.search-clear-btn.active {
  display: block;
}

/* Category Filter Chips */
.category-pills {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  justify-content: center;
}

.category-pill {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  border-radius: var(--radius-full);
  padding: 0.4rem 0.9rem;
  font-size: 0.875rem;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.15s ease;
  user-select: none;
}

.category-pill:hover {
  border-color: var(--border-hover);
  color: var(--text-primary);
  background-color: var(--bg-tertiary);
}

.category-pill.active {
  background-color: var(--accent);
  border-color: var(--accent);
  color: var(--accent-text);
  font-weight: 600;
}

/* Section Titles */
.section-header {
  margin-bottom: 1.25rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.section-title {
  font-size: 1.25rem;
  font-weight: 700;
  letter-spacing: -0.01em;
  color: var(--text-primary);
}

.section-meta {
  font-size: 0.875rem;
  color: var(--text-muted);
}

/* Shape Grid Cards */
.shapes-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: 1.25rem;
}

.shape-card {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  cursor: pointer;
  transition: border-color 0.15s, box-shadow 0.15s, transform 0.15s;
  display: flex;
  flex-direction: column;
  box-shadow: var(--shadow-sm);
  text-decoration: none;
  color: inherit;
}

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

.shape-card:focus-visible {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-ring);
}

.card-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0.85rem;
}

.dim-badge {
  font-size: 0.75rem;
  font-weight: 700;
  padding: 0.2rem 0.5rem;
  border-radius: var(--radius-sm);
  background-color: var(--bg-tertiary);
  color: var(--text-secondary);
  border: 1px solid var(--border-color);
}

.card-illustration {
  height: 90px;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 1rem;
  color: var(--text-secondary);
}

.card-illustration svg {
  height: 100%;
  max-width: 100px;
  stroke: currentColor;
}

.shape-stroke {
  stroke: var(--text-primary);
}

.shape-fill {
  stroke: var(--text-primary);
  fill: var(--bg-tertiary);
}

.card-title {
  font-size: 1.1rem;
  font-weight: 700;
  margin-bottom: 0.35rem;
  color: var(--text-primary);
}

.card-desc {
  font-size: 0.85rem;
  color: var(--text-secondary);
  line-height: 1.4;
  margin-bottom: 1rem;
  flex-grow: 1;
}

.card-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
  margin-top: auto;
}

.card-tag {
  font-size: 0.72rem;
  font-weight: 500;
  padding: 0.15rem 0.45rem;
  border-radius: var(--radius-sm);
  background: var(--bg-tertiary);
  color: var(--text-muted);
}

/* Empty search state */
.no-results {
  grid-column: 1 / -1;
  text-align: center;
  padding: 3rem 1rem;
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  color: var(--text-secondary);
}

.no-results p {
  margin-top: 0.5rem;
  font-size: 0.9rem;
  color: var(--text-muted);
}

/* ============================================================
   Dedicated Calculator View
   ============================================================ */
.calc-view {
  display: none;
}

.calc-view.active {
  display: block;
}

.dashboard-view {
  display: block;
}

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

/* Breadcrumb Navigation */
.breadcrumb-bar {
  margin-bottom: 1.5rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.back-btn {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  padding: 0.4rem 0.8rem;
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  font-size: 0.875rem;
  font-weight: 500;
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  cursor: pointer;
  transition: all 0.15s;
}

.back-btn:hover {
  background: var(--bg-tertiary);
  color: var(--text-primary);
  border-color: var(--border-hover);
}

.breadcrumb-path {
  font-size: 0.875rem;
  color: var(--text-muted);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

/* Shape Banner in Calculator */
.shape-header-card {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  display: flex;
  align-items: center;
  gap: 1.5rem;
  margin-bottom: 1.75rem;
  box-shadow: var(--shadow-sm);
}

.shape-header-svg {
  width: 90px;
  height: 90px;
  flex-shrink: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg-tertiary);
  border-radius: var(--radius-md);
  padding: 0.5rem;
}

.shape-header-svg svg {
  width: 100%;
  height: 100%;
}

.shape-header-info {
  flex: 1;
}

.shape-header-title {
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  margin-bottom: 0.25rem;
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.shape-header-desc {
  font-size: 0.95rem;
  color: var(--text-secondary);
  line-height: 1.45;
}

/* Calculator Grid Layout */
.calculator-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1.75rem;
}

@media (min-width: 900px) {
  .calculator-grid {
    grid-template-columns: 360px 1fr;
  }
}

/* Input Panel Card */
.calc-panel-card {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
  height: fit-content;
}

.calc-panel-title {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text-primary);
  padding-bottom: 0.75rem;
  border-bottom: 1px solid var(--border-color);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

/* Calculation Selectors */
.calc-type-group {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.calc-type-label {
  font-size: 0.825rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--text-secondary);
}

.calc-type-buttons {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.calc-choice-btn {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 0.65rem 0.85rem;
  text-align: left;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  transition: all 0.15s;
  font-family: inherit;
}

.calc-choice-btn:hover {
  background: var(--bg-tertiary);
  border-color: var(--border-hover);
}

.calc-choice-btn.selected {
  background: var(--bg-accent-subtle);
  border-color: var(--accent);
}

.calc-choice-btn.selected .choice-name {
  color: var(--accent);
  font-weight: 600;
}

.choice-name {
  font-size: 0.9rem;
  color: var(--text-primary);
}

.choice-formula {
  font-size: 0.8rem;
  font-family: var(--font-mono);
  color: var(--text-muted);
}

/* Dimensions Input Fields */
.dimensions-group {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.input-row {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}

.input-label-wrap {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.input-label {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-primary);
}

.input-symbol {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--text-muted);
}

.input-field-wrap {
  display: flex;
  align-items: center;
  position: relative;
}

.dim-input {
  width: 100%;
  padding: 0.65rem 0.85rem;
  font-size: 1rem;
  font-family: inherit;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  background: var(--bg-primary);
  color: var(--text-primary);
  outline: none;
  transition: border-color 0.15s, box-shadow 0.15s;
}

.dim-input:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-ring);
}

/* Unit Selector */
.unit-select-wrap {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.unit-label {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-secondary);
}

.unit-dropdown {
  flex: 1;
  padding: 0.55rem 0.75rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  background: var(--bg-secondary);
  color: var(--text-primary);
  font-family: inherit;
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  outline: none;
}

.unit-dropdown:focus {
  border-color: var(--accent);
}

/* Error message banner */
.calc-error {
  display: none;
  background-color: var(--danger-bg);
  border: 1px solid var(--danger-border);
  color: var(--danger);
  padding: 0.75rem 1rem;
  border-radius: var(--radius-sm);
  font-size: 0.875rem;
}

.calc-error.active {
  display: block;
}

/* Calculator Action Buttons */
.calc-actions {
  display: flex;
  gap: 0.75rem;
}

.calc-btn-primary {
  flex: 2;
  background-color: var(--accent);
  color: var(--accent-text);
  border: none;
  border-radius: var(--radius-sm);
  padding: 0.75rem 1.25rem;
  font-size: 1rem;
  font-weight: 600;
  font-family: inherit;
  cursor: pointer;
  transition: background-color 0.15s, transform 0.1s;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
}

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

.calc-btn-primary:active {
  transform: scale(0.99);
}

.calc-btn-secondary {
  flex: 1;
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  border-radius: var(--radius-sm);
  padding: 0.75rem 1rem;
  font-size: 0.95rem;
  font-weight: 500;
  font-family: inherit;
  cursor: pointer;
  transition: all 0.15s;
}

.calc-btn-secondary:hover {
  background-color: var(--bg-tertiary);
  color: var(--text-primary);
}

/* ============================================================
   Calculation Output & Step-by-Step Flow
   ============================================================ */
.calc-output-card {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 1.75rem;
  box-shadow: var(--shadow-sm);
  display: flex;
  flex-direction: column;
  gap: 1.75rem;
}

.calc-placeholder-state {
  text-align: center;
  padding: 3rem 1rem;
  color: var(--text-muted);
}

.calc-placeholder-icon {
  font-size: 2.5rem;
  margin-bottom: 0.75rem;
  opacity: 0.7;
}

/* Result Header & Answer Card */
.result-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.result-tagline {
  font-size: 0.85rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--accent);
}

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

.answer-card {
  background: var(--bg-accent-subtle);
  border: 1.5px solid var(--accent);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.answer-title-group {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.answer-label {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-secondary);
}

.answer-formula-badge {
  font-family: var(--font-mono);
  font-size: 0.875rem;
  background: var(--bg-primary);
  color: var(--text-primary);
  padding: 0.25rem 0.65rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
}

.answer-value-row {
  display: flex;
  align-items: baseline;
  gap: 0.5rem;
  flex-wrap: wrap;
}

.answer-value {
  font-size: 2.5rem;
  font-weight: 800;
  letter-spacing: -0.03em;
  color: var(--text-primary);
  line-height: 1.1;
}

.answer-unit {
  font-size: 1.4rem;
  font-weight: 600;
  color: var(--accent);
}

/* Given Values Summary */
.given-values-wrap {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  padding-top: 0.75rem;
  border-top: 1px dashed var(--border-color);
}

.given-pill {
  font-size: 0.85rem;
  background: var(--bg-primary);
  padding: 0.25rem 0.65rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
}

.given-pill strong {
  color: var(--text-primary);
}

/* Step-by-Step Educational Section */
.steps-section {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.steps-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.steps-title {
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.steps-toggle-btn {
  background: none;
  border: none;
  color: var(--text-secondary);
  font-size: 0.85rem;
  font-family: inherit;
  cursor: pointer;
  text-decoration: underline;
}

.steps-toggle-btn:hover {
  color: var(--accent);
}

.steps-list {
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
}

.step-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1rem 1.25rem;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  position: relative;
  transition: border-color 0.15s;
}

.step-card:hover {
  border-color: var(--border-hover);
}

.step-badge-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.step-badge {
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  color: var(--accent);
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  padding: 0.2rem 0.5rem;
  border-radius: var(--radius-sm);
}

.step-title {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-primary);
}

.step-math {
  font-family: var(--font-mono);
  font-size: 1.05rem;
  font-weight: 600;
  background: var(--bg-primary);
  padding: 0.65rem 0.85rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  color: var(--text-primary);
  overflow-x: auto;
}

.step-desc {
  font-size: 0.875rem;
  color: var(--text-secondary);
  line-height: 1.45;
}

/* Formula Reference Accordion */
.formula-reference-card {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  overflow: hidden;
}

.formula-ref-header {
  padding: 0.85rem 1.25rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  cursor: pointer;
  background: var(--bg-secondary);
  user-select: none;
}

.formula-ref-title {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.formula-ref-icon {
  transition: transform 0.2s ease;
}

.formula-reference-card.open .formula-ref-icon {
  transform: rotate(180deg);
}

.formula-ref-content {
  display: none;
  padding: 1.25rem;
  flex-direction: column;
  gap: 0.75rem;
}

.formula-reference-card.open .formula-ref-content {
  display: flex;
}

.formula-ref-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.5rem 0.75rem;
  background: var(--bg-secondary);
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  font-size: 0.875rem;
}

.formula-ref-name {
  color: var(--text-secondary);
  font-weight: 500;
}

.formula-ref-code {
  font-family: var(--font-mono);
  font-weight: 600;
  color: var(--text-primary);
}

/* Reset / Calculate Again Bar */
.calc-again-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-top: 1rem;
  border-top: 1px solid var(--border-color);
}

/* ============================================================
   Recent History Slide-over Drawer
   ============================================================ */
.drawer-backdrop {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.4);
  z-index: 100;
  display: none;
  opacity: 0;
  transition: opacity 0.2s ease;
}

.drawer-backdrop.active {
  display: block;
  opacity: 1;
}

.drawer {
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  width: 100%;
  max-width: 400px;
  background: var(--bg-primary);
  z-index: 101;
  box-shadow: var(--shadow-lg);
  display: flex;
  flex-direction: column;
  transform: translateX(100%);
  transition: transform 0.25s ease-in-out;
}

.drawer.active {
  transform: translateX(0);
}

.drawer-header {
  padding: 1.25rem;
  border-bottom: 1px solid var(--border-color);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.drawer-title {
  font-size: 1.15rem;
  font-weight: 700;
}

.drawer-close {
  background: none;
  border: none;
  color: var(--text-secondary);
  cursor: pointer;
  padding: 0.25rem;
  font-size: 1.25rem;
  display: flex;
}

.drawer-body {
  flex: 1;
  overflow-y: auto;
  padding: 1.25rem;
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
}

.history-item {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 0.85rem;
  cursor: pointer;
  transition: all 0.15s;
}

.history-item:hover {
  border-color: var(--accent);
  background: var(--bg-accent-subtle);
}

.history-item-top {
  display: flex;
  justify-content: space-between;
  font-size: 0.75rem;
  color: var(--text-muted);
  margin-bottom: 0.35rem;
}

.history-item-shape {
  font-weight: 600;
  color: var(--text-primary);
}

.history-item-calc {
  font-size: 0.85rem;
  color: var(--text-secondary);
  margin-bottom: 0.25rem;
}

.history-item-result {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--accent);
}

.drawer-empty {
  text-align: center;
  color: var(--text-muted);
  margin-top: 4rem;
  font-size: 0.9rem;
}

.drawer-footer {
  padding: 1rem 1.25rem;
  border-top: 1px solid var(--border-color);
}

/* Toast Notifications */
.toast-container {
  position: fixed;
  bottom: 1.5rem;
  right: 1.5rem;
  z-index: 200;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.toast {
  background: var(--text-primary);
  color: var(--bg-primary);
  padding: 0.75rem 1.25rem;
  border-radius: var(--radius-sm);
  font-size: 0.875rem;
  font-weight: 500;
  box-shadow: var(--shadow-lg);
  display: flex;
  align-items: center;
  gap: 0.5rem;
  animation: slideIn 0.2s ease-out;
}

@keyframes slideIn {
  from {
    opacity: 0;
    transform: translateY(10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* Footer */
.footer {
  margin-top: auto;
  background: var(--bg-primary);
  border-top: 1px solid var(--border-color);
  padding: 1.5rem 1.25rem;
  text-align: center;
  font-size: 0.85rem;
  color: var(--text-secondary);
}

.footer-content {
  max-width: 1200px;
  margin: 0 auto;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.35rem;
}

/* Responsive Tweaks */
@media (max-width: 640px) {
  .header-container {
    padding: 0.75rem 1rem;
  }
  
  .logo-title {
    font-size: 1.1rem;
  }

  .logo-tagline {
    display: none;
  }

  .pi-selector-wrap span {
    display: none;
  }

  .shape-header-card {
    flex-direction: column;
    text-align: center;
    gap: 1rem;
  }

  .shape-header-title {
    justify-content: center;
  }

  .answer-value {
    font-size: 2rem;
  }

  .category-pill {
    padding: 0.35rem 0.75rem;
    font-size: 0.8rem;
  }
}

/* ============================================================
   SEO & Educational Content Section Extensions
   ============================================================ */
.edu-section {
  margin-top: 3rem;
  display: flex;
  flex-direction: column;
  gap: 2rem;
}

.edu-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 1.5rem;
}

.edu-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
  box-shadow: var(--shadow-sm);
}

.edu-card-title {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.edu-card-desc {
  font-size: 0.925rem;
  color: var(--text-secondary);
  line-height: 1.65;
}

.edu-formula-highlight {
  font-family: var(--font-mono);
  background: var(--bg-tertiary);
  border: 1px solid var(--border-color);
  padding: 0.6rem 0.9rem;
  border-radius: var(--radius-sm);
  color: var(--accent);
  font-size: 0.95rem;
  font-weight: 600;
  display: inline-block;
  margin: 0.25rem 0;
}

.manual-calc-box {
  background: var(--bg-tertiary);
  border: 1px solid var(--border-color);
  border-left: 4px solid var(--accent);
  border-radius: var(--radius-sm);
  padding: 1rem 1.25rem;
  font-size: 0.9rem;
  color: var(--text-primary);
  line-height: 1.6;
}

.manual-calc-box ol, .manual-calc-box ul {
  margin-left: 1.25rem;
  margin-top: 0.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}

.manual-calc-box li {
  color: var(--text-secondary);
}

.manual-calc-math {
  font-family: var(--font-mono);
  font-weight: 600;
  color: var(--text-primary);
  background: var(--bg-card);
  padding: 0.15rem 0.4rem;
  border-radius: 4px;
  border: 1px solid var(--border-color);
}

.edu-disclaimer {
  background: var(--bg-accent-subtle);
  border: 1px solid var(--accent-light);
  border-radius: var(--radius-sm);
  padding: 0.85rem 1rem;
  font-size: 0.85rem;
  color: var(--text-secondary);
  line-height: 1.5;
  display: flex;
  align-items: flex-start;
  gap: 0.6rem;
}

.edu-disclaimer-icon {
  color: var(--accent);
  flex-shrink: 0;
  margin-top: 2px;
}

/* FAQ Accordions */
.faq-section-title {
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 1rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

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

.faq-item {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  overflow: hidden;
  transition: border-color 0.2s;
}

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

.faq-question-btn {
  width: 100%;
  background: none;
  border: none;
  padding: 1.1rem 1.25rem;
  text-align: left;
  font-size: 0.975rem;
  font-weight: 600;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  cursor: pointer;
}

.faq-chevron {
  transition: transform 0.2s ease;
  color: var(--text-muted);
  flex-shrink: 0;
}

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

.faq-answer {
  display: none;
  padding: 0 1.25rem 1.1rem 1.25rem;
  font-size: 0.925rem;
  color: var(--text-secondary);
  line-height: 1.65;
  border-top: 1px solid var(--border-color);
  background: var(--bg-secondary);
}

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

/* Related Calculators Grid */
.related-section-title {
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 1rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.related-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 1rem;
}

.related-card {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.15rem;
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
  text-decoration: none;
  color: inherit;
  transition: all 0.2s ease;
  cursor: pointer;
}

.related-card:hover {
  border-color: var(--accent);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.related-card-title {
  font-size: 0.975rem;
  font-weight: 600;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.related-card-arrow {
  color: var(--accent);
  font-size: 1.1rem;
  transition: transform 0.2s;
}

.related-card:hover .related-card-arrow {
  transform: translateX(3px);
}

.related-card-desc {
  font-size: 0.825rem;
  color: var(--text-muted);
  line-height: 1.4;
}

/* Input group with inline unit select */
.input-field-with-unit {
  display: flex;
  gap: 0.5rem;
}

.input-field-with-unit .dim-input {
  flex: 1;
}

.input-unit-select {
  background: var(--bg-tertiary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  padding: 0 0.6rem;
  font-size: 0.85rem;
  font-weight: 500;
  color: var(--text-primary);
  outline: none;
  cursor: pointer;
}

.input-unit-select:focus {
  border-color: var(--border-focus);
}

/* Surface Area Calculator Options on Home Page */
.sa-options-container {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  padding: 1.1rem 1.25rem;
  background-color: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  margin-top: 0.25rem;
}

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

.sa-options-title {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.sa-options-list {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.sa-option-btn {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  color: var(--text-primary);
  border-radius: var(--radius-full);
  padding: 0.45rem 0.95rem;
  font-size: 0.825rem;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.15s ease;
  font-family: inherit;
  display: inline-flex;
  align-items: center;
  text-decoration: none;
}

.sa-option-btn:hover {
  background-color: var(--accent);
  border-color: var(--accent);
  color: var(--accent-text);
  transform: translateY(-1px);
  box-shadow: var(--shadow-sm);
}

/* ============================================================
   Footer Navigation Links & Brand
   ============================================================ */
.footer-nav {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 0.6rem 1.15rem;
  margin-top: 0.85rem;
  padding-top: 0.85rem;
  border-top: 1px solid var(--border-color);
  width: 100%;
  max-width: 620px;
}

.footer-nav-link {
  color: var(--text-secondary);
  text-decoration: none;
  font-size: 0.835rem;
  font-weight: 500;
  transition: color 0.15s ease;
}

.footer-nav-link:hover,
.footer-nav-link:focus-visible {
  color: var(--accent);
  text-decoration: underline;
  outline: none;
}

.footer-nav-divider {
  color: var(--text-muted);
  font-size: 0.75rem;
  user-select: none;
}

/* ============================================================
   Content Pages (About, Privacy, Terms, Contact)
   ============================================================ */
.content-wrapper {
  max-width: 960px;
  width: 100%;
  margin: 0 auto;
  padding: 2rem 1.25rem 4rem 1.25rem;
  display: flex;
  flex-direction: column;
  gap: 1.75rem;
}

.page-header-card {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 2.25rem 2rem;
  box-shadow: var(--shadow-sm);
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.page-header-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.25rem 0.65rem;
  background-color: var(--bg-accent-subtle);
  color: var(--accent);
  border-radius: var(--radius-full);
  font-size: 0.75rem;
  font-weight: 600;
  width: fit-content;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.page-title {
  font-size: 2.15rem;
  font-weight: 800;
  color: var(--text-primary);
  letter-spacing: -0.025em;
  line-height: 1.2;
}

.page-subtitle {
  font-size: 1.05rem;
  color: var(--text-secondary);
  line-height: 1.6;
  max-width: 760px;
}

.page-meta-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 1.25rem;
  font-size: 0.825rem;
  color: var(--text-muted);
  padding-top: 0.85rem;
  border-top: 1px solid var(--border-color);
}

.content-card {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 2.25rem;
  box-shadow: var(--shadow-sm);
  display: flex;
  flex-direction: column;
  gap: 2rem;
}

.prose-section {
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
}

.prose-section h2 {
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: -0.015em;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.prose-section h3 {
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-top: 0.5rem;
}

.prose-section p {
  font-size: 0.95rem;
  color: var(--text-secondary);
  line-height: 1.7;
}

.prose-section ul, .prose-section ol {
  padding-left: 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.prose-section li {
  font-size: 0.95rem;
  color: var(--text-secondary);
  line-height: 1.6;
}

.prose-callout {
  background: var(--bg-secondary);
  border-left: 4px solid var(--accent);
  padding: 1.1rem 1.25rem;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  font-size: 0.925rem;
  color: var(--text-secondary);
  line-height: 1.6;
}

.prose-callout.warning {
  border-left-color: #f59e0b;
  background: #fffbeb;
  color: #92400e;
}
[data-theme="dark"] .prose-callout.warning {
  background: #451a03;
  color: #fde68a;
  border-left-color: #f59e0b;
}

/* Contact Grid & Form */
.contact-layout {
  display: grid;
  grid-template-columns: 1fr 1.35fr;
  gap: 1.75rem;
}

@media (max-width: 800px) {
  .contact-layout {
    grid-template-columns: 1fr;
  }
}

.contact-info-list {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.contact-info-card {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
}

.contact-info-title {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.contact-info-text {
  font-size: 0.875rem;
  color: var(--text-secondary);
  line-height: 1.5;
}

.contact-info-text a {
  color: var(--accent);
  text-decoration: none;
}

.contact-info-text a:hover {
  text-decoration: underline;
}

.contact-form {
  display: flex;
  flex-direction: column;
  gap: 1.15rem;
}

.form-group {
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
}

.form-label {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-primary);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.form-required {
  color: var(--danger);
  margin-left: 0.2rem;
}

.form-input, .form-textarea, .form-select-custom {
  width: 100%;
  padding: 0.75rem 0.95rem;
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  color: var(--text-primary);
  font-family: inherit;
  font-size: 0.925rem;
  outline: none;
  transition: border-color 0.15s, box-shadow 0.15s;
}

.form-input:focus, .form-textarea:focus, .form-select-custom:focus {
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px var(--accent-ring);
  background: var(--bg-primary);
}

.form-input.is-invalid, .form-textarea.is-invalid, .form-select-custom.is-invalid {
  border-color: var(--danger);
}

.form-error-msg {
  font-size: 0.775rem;
  color: var(--danger);
  min-height: 1rem;
}

.form-alert {
  padding: 0.95rem 1.15rem;
  border-radius: var(--radius-sm);
  font-size: 0.875rem;
  line-height: 1.5;
  display: none;
}

.form-alert.success {
  background-color: var(--success-bg);
  border: 1px solid var(--success);
  color: var(--success);
}

.form-alert.error {
  background-color: var(--danger-bg);
  border: 1px solid var(--danger-border);
  color: var(--danger);
}

.form-alert.info {
  background-color: var(--bg-accent-subtle);
  border: 1px solid var(--accent-light);
  color: var(--accent);
}

/* Error Pages (404, 500) */
.error-page-wrapper {
  max-width: 680px;
  width: 100%;
  margin: 3rem auto;
  padding: 0 1.25rem;
  text-align: center;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1.5rem;
}

.error-hero-card {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 3rem 2rem;
  box-shadow: var(--shadow-md);
  width: 100%;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
}

.error-code-badge {
  font-family: var(--font-mono);
  font-size: 4.5rem;
  font-weight: 800;
  line-height: 1;
  color: var(--accent);
  letter-spacing: -0.05em;
}

.error-tag {
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  background: var(--bg-tertiary);
  padding: 0.25rem 0.75rem;
  border-radius: var(--radius-full);
}

.error-title {
  font-size: 1.65rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-top: 0.25rem;
}

.error-description {
  font-size: 0.975rem;
  color: var(--text-secondary);
  line-height: 1.6;
  max-width: 480px;
}

.error-actions-group {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  justify-content: center;
  margin-top: 0.75rem;
}

.error-quick-links {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  width: 100%;
  margin-top: 0.5rem;
  text-align: left;
}

.error-quick-links-title {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.75rem;
}

.error-links-chips {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.error-chip {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  padding: 0.35rem 0.75rem;
  border-radius: var(--radius-full);
  font-size: 0.8rem;
  color: var(--text-primary);
  text-decoration: none;
  transition: all 0.15s;
}

.error-chip:hover {
  border-color: var(--accent);
  color: var(--accent);
}