/* ============================================================
   BIT Technical Interview Study Guide — Shared Stylesheet
   ============================================================ */

:root {
  --blue-dark:   #1a3a5c;
  --blue-mid:    #2563a8;
  --blue-light:  #d5e8f0;
  --blue-pale:   #eaf4fb;
  --accent:      #f0a500;
  --accent-pale: #fff8e6;
  --text:        #1a1a2e;
  --text-light:  #4a5568;
  --white:       #ffffff;
  --border:      #ccd9e8;
  --shadow:      rgba(26, 58, 92, 0.10);
  --nav-height:  64px;
}

/* ---- Reset ---- */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: 'Segoe UI', Arial, sans-serif;
  font-size: 16px;
  line-height: 1.7;
  color: var(--text);
  background: #f4f8fb;
  padding-top: var(--nav-height);
}

/* ---- Top Navigation ---- */
nav.topnav {
  position: fixed;
  top: 0; left: 0; right: 0;
  height: var(--nav-height);
  background: var(--blue-dark);
  display: flex;
  align-items: center;
  padding: 0 1.5rem;
  gap: 0.25rem;
  z-index: 1000;
  box-shadow: 0 2px 8px rgba(0,0,0,0.25);
  overflow-x: auto;
  overflow-y: hidden;
  flex-wrap: nowrap;
}

nav.topnav a {
  color: #c9dff5;
  text-decoration: none;
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.02em;
  padding: 0.35rem 0.65rem;
  border-radius: 4px;
  white-space: nowrap;
  transition: background 0.18s, color 0.18s;
}

nav.topnav a:hover,
nav.topnav a.active {
  background: var(--blue-mid);
  color: var(--white);
}

nav.topnav .nav-home {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--accent);
  margin-right: 0.5rem;
  border-right: 1px solid #2d5a8a;
  padding-right: 0.75rem;
}

nav.topnav .nav-home:hover {
  background: transparent;
  color: var(--accent);
  opacity: 0.85;
}

/* ---- Page Container ---- */
.page-container {
  max-width: 880px;
  margin: 2.5rem auto;
  padding: 0 1.25rem;
}

/* ---- Page Header ---- */
.page-header {
  background: var(--blue-dark);
  color: var(--white);
  border-radius: 10px 10px 0 0;
  padding: 2.25rem 2.5rem 1.75rem;
  position: relative;
  overflow: hidden;
}

.page-header::after {
  content: '';
  position: absolute;
  bottom: -12px; left: 0; right: 0;
  height: 24px;
  background: #f4f8fb;
  border-radius: 50% 50% 0 0 / 100% 100% 0 0;
  transform: scaleX(1.05);
}

.page-label {
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 0.5rem;
}

.page-header h1 {
  font-size: 2rem;
  font-weight: 700;
  line-height: 1.2;
  color: var(--white);
}

/* ---- Content Card ---- */
.content-card {
  background: var(--white);
  border-radius: 0 0 10px 10px;
  padding: 2.25rem 2.5rem;
  box-shadow: 0 4px 16px var(--shadow);
  margin-bottom: 1.5rem;
}

/* ---- Section Headings ---- */
h2 {
  font-size: 1.3rem;
  font-weight: 700;
  color: var(--blue-dark);
  margin-top: 2rem;
  margin-bottom: 0.75rem;
  padding-bottom: 0.4rem;
  border-bottom: 2px solid var(--blue-light);
}

h2:first-child { margin-top: 0; }

h3 {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--blue-mid);
  margin-top: 1.5rem;
  margin-bottom: 0.5rem;
}

p { margin-bottom: 1rem; }

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

.callout.accent {
  background: var(--accent-pale);
  border-left-color: var(--accent);
}

.callout .callout-label {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--blue-mid);
  margin-bottom: 0.4rem;
}

.callout.accent .callout-label { color: #b07800; }

.callout p:last-child { margin-bottom: 0; }

/* ---- Tables ---- */
.table-wrap { overflow-x: auto; margin: 1.25rem 0; }

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.93rem;
}

thead th {
  background: var(--blue-dark);
  color: var(--white);
  text-align: left;
  padding: 0.65rem 0.9rem;
  font-weight: 700;
  font-size: 0.82rem;
  letter-spacing: 0.04em;
}

tbody tr:nth-child(even) { background: var(--blue-pale); }
tbody tr:nth-child(odd)  { background: var(--white); }

tbody td {
  padding: 0.6rem 0.9rem;
  border-bottom: 1px solid var(--border);
  vertical-align: top;
}

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

/* ---- Lists ---- */
ul, ol {
  margin: 0.5rem 0 1rem 1.5rem;
}

li { margin-bottom: 0.4rem; }

/* ---- Stat Badges ---- */
.stat-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1rem;
  margin: 1.25rem 0;
}

.stat-card {
  background: var(--blue-pale);
  border: 1px solid var(--blue-light);
  border-radius: 8px;
  padding: 1rem 1.1rem;
  text-align: center;
}

.stat-card .stat-number {
  font-size: 1.6rem;
  font-weight: 800;
  color: var(--blue-dark);
  line-height: 1;
  margin-bottom: 0.3rem;
}

.stat-card .stat-label {
  font-size: 0.83rem;
  color: var(--text-light);
  line-height: 1.4;
}

/* ---- Bottom Navigation ---- */
.page-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1.25rem 0 2rem;
  gap: 1rem;
}

.page-nav a {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: var(--blue-dark);
  color: var(--white);
  text-decoration: none;
  font-weight: 700;
  font-size: 0.9rem;
  padding: 0.65rem 1.25rem;
  border-radius: 6px;
  transition: background 0.18s, transform 0.1s;
}

.page-nav a:hover {
  background: var(--blue-mid);
  transform: translateY(-1px);
}

.page-nav .nav-label {
  font-size: 0.72rem;
  font-weight: 400;
  opacity: 0.75;
  display: block;
  line-height: 1;
}

.page-nav .spacer { flex: 1; }

/* ---- Index / TOC Page ---- */
.toc-hero {
  background: linear-gradient(135deg, var(--blue-dark) 60%, var(--blue-mid));
  border-radius: 10px;
  padding: 3rem 2.5rem 2.5rem;
  color: var(--white);
  margin-bottom: 1.5rem;
  box-shadow: 0 4px 20px var(--shadow);
}

.toc-hero h1 {
  font-size: 2.2rem;
  font-weight: 800;
  line-height: 1.15;
  margin-bottom: 0.75rem;
}

.toc-hero .subtitle {
  font-size: 1.05rem;
  color: #c9dff5;
  margin-bottom: 1.5rem;
}

.toc-hero .interview-box {
  background: rgba(255,255,255,0.1);
  border: 1px solid rgba(255,255,255,0.2);
  border-radius: 8px;
  padding: 1.1rem 1.4rem;
}

.toc-hero .interview-box h3 {
  color: var(--accent);
  font-size: 0.82rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  margin-bottom: 0.6rem;
  margin-top: 0;
}

.toc-hero .interview-box ol {
  margin: 0 0 0 1.25rem;
  color: #e8f2fc;
}

.toc-hero .interview-box li { margin-bottom: 0.4rem; font-size: 0.95rem; }

.toc-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 1rem;
  margin-bottom: 2rem;
}

.toc-card {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1.25rem 1.4rem;
  text-decoration: none;
  color: var(--text);
  display: block;
  transition: border-color 0.18s, box-shadow 0.18s, transform 0.12s;
  box-shadow: 0 2px 6px var(--shadow);
}

.toc-card:hover {
  border-color: var(--blue-mid);
  box-shadow: 0 6px 18px rgba(37,99,168,0.15);
  transform: translateY(-2px);
}

.toc-card .card-num {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--blue-mid);
  margin-bottom: 0.3rem;
}

.toc-card h3 {
  font-size: 1rem;
  font-weight: 700;
  color: var(--blue-dark);
  margin: 0 0 0.3rem;
}

.toc-card p {
  font-size: 0.83rem;
  color: var(--text-light);
  margin: 0;
}

/* ---- Responsive ---- */
@media (max-width: 640px) {
  .page-header { padding: 1.5rem 1.25rem 1.25rem; }
  .page-header h1 { font-size: 1.5rem; }
  .content-card { padding: 1.5rem 1.25rem; }
  .toc-hero { padding: 2rem 1.25rem; }
  .toc-hero h1 { font-size: 1.6rem; }
  nav.topnav a { font-size: 0.72rem; padding: 0.3rem 0.5rem; }
}