/* ENEE 154 Electrical Circuits and Machines - Master Engineering Stylesheet */

:root {
  --bg-body: #f8fafc;
  --bg-surface: #ffffff;
  --bg-surface-elevated: #f1f5f9;
  --bg-sidebar: #ffffff;
  --border-color: #e2e8f0;
  --border-focus: #3b82f6;
  
  --text-main: #0f172a;
  --text-muted: #64748b;
  --text-light: #94a3b8;
  
  --primary: #2563eb;
  --primary-hover: #1d4ed8;
  --primary-light: #eff6ff;
  
  --accent-cyan: #0284c7;
  --accent-teal: #0d9488;
  
  --badge-high-bg: #fee2e2;
  --badge-high-text: #b91c1c;
  --badge-med-bg: #fef3c7;
  --badge-med-text: #b45309;
  --badge-low-bg: #dcfce7;
  --badge-low-text: #15803d;
  --badge-pyq-bg: #ede9fe;
  --badge-pyq-text: #6d28d9;

  --callout-info-bg: #eff6ff;
  --callout-info-border: #3b82f6;
  --callout-warn-bg: #fffbeb;
  --callout-warn-border: #f59e0b;
  --callout-danger-bg: #fef2f2;
  --callout-danger-border: #ef4444;
  --callout-success-bg: #f0fdf4;
  --callout-success-border: #22c55e;
  
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
  
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
  
  --sidebar-width: 290px;
  --header-height: 64px;
}

[data-theme="dark"] {
  --bg-body: #0b0f19;
  --bg-surface: #111827;
  --bg-surface-elevated: #1f2937;
  --bg-sidebar: #0f172a;
  --border-color: #1f2937;
  --border-focus: #60a5fa;
  
  --text-main: #f3f4f6;
  --text-muted: #9ca3af;
  --text-light: #6b7280;
  
  --primary: #3b82f6;
  --primary-hover: #60a5fa;
  --primary-light: #1e293b;
  
  --accent-cyan: #38bdf8;
  --accent-teal: #2dd4bf;
  
  --badge-high-bg: #450a0a;
  --badge-high-text: #fca5a5;
  --badge-med-bg: #451a03;
  --badge-med-text: #fcd34d;
  --badge-low-bg: #052e16;
  --badge-low-text: #86efac;
  --badge-pyq-bg: #2e1065;
  --badge-pyq-text: #d8b4fe;

  --callout-info-bg: #172554;
  --callout-info-border: #3b82f6;
  --callout-warn-bg: #451a03;
  --callout-warn-border: #f59e0b;
  --callout-danger-bg: #450a0a;
  --callout-danger-border: #ef4444;
  --callout-success-bg: #052e16;
  --callout-success-border: #22c55e;
  
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.5);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.4);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.5);
}

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

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

body {
  font-family: var(--font-sans);
  background-color: var(--bg-body);
  color: var(--text-main);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  color: var(--text-main);
  font-weight: 700;
  line-height: 1.3;
  margin-top: 1.5rem;
  margin-bottom: 0.75rem;
}

h1 { font-size: 2.1rem; letter-spacing: -0.025em; }
h2 { font-size: 1.6rem; border-bottom: 2px solid var(--border-color); padding-bottom: 0.4rem; margin-top: 2rem; }
h3 { font-size: 1.25rem; }
h4 { font-size: 1.1rem; }

p {
  margin-bottom: 1rem;
}

a {
  color: var(--primary);
  text-decoration: none;
  transition: color 0.15s ease;
}

a:hover {
  color: var(--primary-hover);
  text-decoration: underline;
}

code, kbd, samp, pre {
  font-family: var(--font-mono);
}

code {
  background: var(--bg-surface-elevated);
  padding: 0.15rem 0.4rem;
  border-radius: 4px;
  font-size: 0.9em;
  color: var(--primary);
  border: 1px solid var(--border-color);
}

pre {
  background: var(--bg-surface-elevated);
  padding: 1rem;
  border-radius: 8px;
  overflow-x: auto;
  border: 1px solid var(--border-color);
  margin-bottom: 1.25rem;
}

/* Layout */
.app-header {
  position: sticky;
  top: 0;
  height: var(--header-height);
  background: var(--bg-surface);
  border-bottom: 1px solid var(--border-color);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 1.5rem;
  z-index: 100;
  box-shadow: var(--shadow-sm);
}

.header-brand {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--text-main);
  text-decoration: none !important;
}

.brand-badge {
  background: var(--primary);
  color: white;
  padding: 0.2rem 0.55rem;
  border-radius: 6px;
  font-size: 0.75rem;
  font-weight: 800;
  letter-spacing: 0.05em;
}

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

.search-box-btn {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.45rem 0.85rem;
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-color);
  border-radius: 8px;
  color: var(--text-muted);
  cursor: pointer;
  font-size: 0.875rem;
  transition: all 0.2s ease;
}

.search-box-btn:hover {
  border-color: var(--border-focus);
  color: var(--text-main);
}

.theme-toggle-btn, .mobile-menu-btn {
  background: transparent;
  border: 1px solid var(--border-color);
  border-radius: 8px;
  width: 38px;
  height: 38px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-main);
  cursor: pointer;
  transition: background 0.15s ease;
}

.theme-toggle-btn:hover, .mobile-menu-btn:hover {
  background: var(--bg-surface-elevated);
}

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

/* App Body with Sidebar */
.app-container {
  display: flex;
  min-height: calc(100vh - var(--header-height));
}

.sidebar {
  width: var(--sidebar-width);
  background: var(--bg-sidebar);
  border-right: 1px solid var(--border-color);
  overflow-y: auto;
  position: sticky;
  top: var(--header-height);
  height: calc(100vh - var(--header-height));
  padding: 1.25rem 1rem;
  flex-shrink: 0;
}

.sidebar-heading {
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-light);
  margin-top: 1.25rem;
  margin-bottom: 0.5rem;
  padding-left: 0.5rem;
}

.sidebar-nav {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.2rem;
}

.sidebar-link {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.45rem 0.65rem;
  border-radius: 6px;
  color: var(--text-muted);
  font-size: 0.88rem;
  font-weight: 500;
  text-decoration: none !important;
  transition: all 0.15s ease;
}

.sidebar-link:hover {
  background: var(--bg-surface-elevated);
  color: var(--text-main);
}

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

.sidebar-link-badge {
  font-size: 0.7rem;
  padding: 0.1rem 0.4rem;
  border-radius: 4px;
  background: var(--bg-surface-elevated);
  color: var(--text-light);
}

.sidebar-link.active .sidebar-link-badge {
  background: var(--primary);
  color: white;
}

.main-content {
  flex: 1;
  max-width: 1040px;
  padding: 2.25rem 3rem 4rem 3rem;
  margin: 0 auto;
}

/* Badges */
.badge {
  display: inline-flex;
  align-items: center;
  gap: 0.25rem;
  font-size: 0.75rem;
  font-weight: 700;
  padding: 0.2rem 0.6rem;
  border-radius: 9999px;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  vertical-align: middle;
}

.badge-high { background: var(--badge-high-bg); color: var(--badge-high-text); }
.badge-med { background: var(--badge-med-bg); color: var(--badge-med-text); }
.badge-low { background: var(--badge-low-bg); color: var(--badge-low-text); }
.badge-pyq { background: var(--badge-pyq-bg); color: var(--badge-pyq-text); }

/* Callout Boxes */
.callout {
  padding: 1rem 1.25rem;
  border-left: 4px solid;
  border-radius: 0 8px 8px 0;
  margin: 1.25rem 0;
  background: var(--bg-surface-elevated);
}

.callout-title {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-weight: 700;
  margin-bottom: 0.4rem;
}

.callout-info {
  background: var(--callout-info-bg);
  border-left-color: var(--callout-info-border);
}

.callout-warn {
  background: var(--callout-warn-bg);
  border-left-color: var(--callout-warn-border);
}

.callout-danger {
  background: var(--callout-danger-bg);
  border-left-color: var(--callout-danger-border);
}

.callout-success {
  background: var(--callout-success-bg);
  border-left-color: var(--callout-success-border);
}

/* Cards & Containers */
.card {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: 12px;
  padding: 1.5rem;
  margin: 1.25rem 0;
  box-shadow: var(--shadow-sm);
  transition: box-shadow 0.2s ease, border-color 0.2s ease;
}

.card:hover {
  border-color: var(--border-focus);
  box-shadow: var(--shadow-md);
}

.card-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  margin-bottom: 0.75rem;
}

.card-title {
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--text-main);
  margin: 0;
}

/* Formula Callout Block */
.formula-block {
  background: var(--bg-surface-elevated);
  border: 1px solid var(--border-color);
  border-radius: 10px;
  padding: 1.25rem;
  margin: 1.25rem 0;
  text-align: center;
  box-shadow: var(--shadow-sm);
}

.formula-math {
  font-size: 1.25rem;
  font-weight: 600;
  margin-bottom: 0.5rem;
  color: var(--primary);
  font-family: var(--font-mono);
  overflow-x: auto;
  padding: 0.4rem 0;
}

.formula-meta {
  font-size: 0.85rem;
  color: var(--text-muted);
  text-align: left;
  border-top: 1px dashed var(--border-color);
  padding-top: 0.6rem;
  margin-top: 0.6rem;
}

/* Worked Numerical Step-by-Step Standard */
.worked-example {
  background: var(--bg-surface);
  border: 2px solid var(--border-color);
  border-radius: 12px;
  margin: 1.75rem 0;
  overflow: hidden;
  box-shadow: var(--shadow-md);
}

.example-header {
  background: var(--primary-light);
  border-bottom: 1px solid var(--border-color);
  padding: 0.85rem 1.25rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.example-title {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--primary);
  margin: 0;
}

.example-body {
  padding: 1.25rem;
}

.step-label {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 800;
  text-transform: uppercase;
  color: var(--primary);
  background: var(--primary-light);
  padding: 0.15rem 0.5rem;
  border-radius: 4px;
  margin-bottom: 0.25rem;
  margin-top: 0.5rem;
}

.step-content {
  margin-left: 0.5rem;
  margin-bottom: 0.75rem;
}

.step-final-answer {
  background: var(--callout-success-bg);
  border: 1px solid var(--callout-success-border);
  padding: 0.85rem 1.25rem;
  border-radius: 8px;
  margin-top: 1rem;
  font-weight: 600;
  color: var(--text-main);
}

/* Tables */
.table-container {
  overflow-x: auto;
  margin: 1.5rem 0;
  border: 1px solid var(--border-color);
  border-radius: 10px;
  box-shadow: var(--shadow-sm);
}

table {
  width: 100%;
  border-collapse: collapse;
  text-align: left;
  font-size: 0.92rem;
  background: var(--bg-surface);
}

th, td {
  padding: 0.8rem 1rem;
  border-bottom: 1px solid var(--border-color);
}

th {
  background: var(--bg-surface-elevated);
  font-weight: 700;
  color: var(--text-main);
}

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

tr:hover td {
  background: var(--bg-surface-elevated);
}

/* Collapsible Accordions (details/summary) */
details {
  border: 1px solid var(--border-color);
  border-radius: 8px;
  margin: 0.85rem 0;
  background: var(--bg-surface);
  transition: all 0.2s ease;
}

details[open] {
  border-color: var(--primary);
  box-shadow: var(--shadow-sm);
}

summary {
  padding: 0.85rem 1.15rem;
  font-weight: 600;
  cursor: pointer;
  user-select: none;
  display: flex;
  align-items: center;
  justify-content: space-between;
  list-style: none;
}

summary::-webkit-details-marker {
  display: none;
}

summary::after {
  content: "+";
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--text-muted);
  transition: transform 0.2s ease;
}

details[open] summary::after {
  content: "−";
  color: var(--primary);
}

.details-content {
  padding: 1rem 1.25rem;
  border-top: 1px solid var(--border-color);
  background: var(--bg-surface);
}

/* Chapter Navigation (Bottom Prev/Next) */
.chapter-nav {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 3.5rem;
  padding-top: 1.5rem;
  border-top: 2px solid var(--border-color);
}

.chapter-nav-btn {
  display: flex;
  flex-direction: column;
  padding: 0.85rem 1.25rem;
  border: 1px solid var(--border-color);
  border-radius: 10px;
  background: var(--bg-surface);
  text-decoration: none !important;
  transition: all 0.2s ease;
  min-width: 220px;
}

.chapter-nav-btn:hover {
  border-color: var(--primary);
  background: var(--bg-surface-elevated);
}

.chapter-nav-label {
  font-size: 0.75rem;
  text-transform: uppercase;
  color: var(--text-muted);
  font-weight: 700;
}

.chapter-nav-title {
  font-size: 1rem;
  font-weight: 700;
  color: var(--primary);
}

/* Modal Search Overlay */
.search-modal {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: rgba(0, 0, 0, 0.6);
  backdrop-filter: blur(4px);
  display: none;
  align-items: flex-start;
  justify-content: center;
  padding-top: 10vh;
  z-index: 1000;
}

.search-modal.active {
  display: flex;
}

.search-container {
  background: var(--bg-surface);
  width: 90%;
  max-width: 650px;
  border-radius: 12px;
  border: 1px solid var(--border-color);
  box-shadow: var(--shadow-lg);
  overflow: hidden;
}

.search-input-wrapper {
  display: flex;
  align-items: center;
  padding: 1rem 1.25rem;
  border-bottom: 1px solid var(--border-color);
}

.search-input {
  flex: 1;
  border: none;
  background: transparent;
  font-size: 1.1rem;
  color: var(--text-main);
  outline: none;
  font-family: var(--font-sans);
}

.search-results {
  max-height: 400px;
  overflow-y: auto;
  padding: 0.75rem;
}

.search-result-item {
  padding: 0.75rem 1rem;
  border-radius: 8px;
  display: block;
  text-decoration: none !important;
  color: var(--text-main);
  transition: background 0.15s ease;
}

.search-result-item:hover {
  background: var(--bg-surface-elevated);
}

.search-result-title {
  font-weight: 700;
  color: var(--primary);
  font-size: 0.95rem;
}

.search-result-context {
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-top: 0.2rem;
}

/* SVG Schematics styling */
.schematic-box {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: 10px;
  padding: 1.25rem;
  margin: 1.25rem 0;
  text-align: center;
}

.schematic-box svg {
  max-width: 100%;
  height: auto;
}

.schematic-caption {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-top: 0.75rem;
  font-weight: 500;
}

/* Responsive */
@media (max-width: 900px) {
  .sidebar {
    position: fixed;
    left: -100%;
    top: var(--header-height);
    z-index: 90;
    transition: left 0.3s ease;
    box-shadow: var(--shadow-lg);
  }

  .sidebar.open {
    left: 0;
  }

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

  .main-content {
    padding: 1.5rem 1.25rem 3rem 1.25rem;
  }

  .chapter-nav {
    flex-direction: column;
  }

  .chapter-nav-btn {
    min-width: 100%;
  }
}