/* ===== CSS VARIABLES & DESIGN TOKENS ===== */
:root {
  --bg-primary: #0f1117;
  --bg-secondary: #1a1d27;
  --bg-tertiary: #232735;
  --bg-card: #1e2130;
  --bg-code: #151822;
  --text-primary: #e8eaf0;
  --text-secondary: #a0a4b8;
  --text-muted: #6b7089;
  --accent: #6c63ff;
  --accent-hover: #5a52e0;
  --accent-glow: rgba(108, 99, 255, 0.15);
  --accent-green: #22c55e;
  --accent-orange: #f59e0b;
  --accent-red: #ef4444;
  --accent-cyan: #06b6d4;
  --border: #2a2e3e;
  --sidebar-width: 280px;
  --header-height: 60px;
  --radius: 10px;
  --radius-sm: 6px;
  --shadow: 0 4px 24px rgba(0,0,0,0.25);
  --transition: 0.25s cubic-bezier(0.4,0,0.2,1);
  --font: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Consolas', monospace;
}

[data-theme="light"] {
  --bg-primary: #f5f7fb;
  --bg-secondary: #ffffff;
  --bg-tertiary: #eef1f8;
  --bg-card: #ffffff;
  --bg-code: #f0f2f8;
  --text-primary: #1a1d2e;
  --text-secondary: #4a5068;
  --text-muted: #8890a8;
  --border: #dde1ed;
  --shadow: 0 4px 24px rgba(0,0,0,0.08);
}

/* ===== RESET & BASE ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--font);
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.7;
  overflow-x: hidden;
  transition: background var(--transition), color var(--transition);
}
a { color: var(--accent); text-decoration: none; transition: color var(--transition); }
a:hover { color: var(--accent-hover); }
img { max-width: 100%; }
ul, ol { padding-left: 1.5em; }
h1,h2,h3,h4,h5,h6 { line-height: 1.3; font-weight: 700; }

/* ===== LAYOUT ===== */
.app-container { display: flex; min-height: 100vh; }

/* ===== HEADER ===== */
.header {
  position: fixed; top: 0; left: var(--sidebar-width); right: 0;
  height: var(--header-height); z-index: 100;
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border);
  display: flex; align-items: center; justify-content: space-between;
  padding: 0 2rem;
  backdrop-filter: blur(12px);
  transition: left var(--transition), background var(--transition);
}
.header-left { display: flex; align-items: center; gap: 1rem; }
.header-right { display: flex; align-items: center; gap: 1rem; }
.hamburger {
  display: none; background: none; border: none; color: var(--text-primary);
  font-size: 1.5rem; cursor: pointer; padding: 0.25rem;
}
.search-box {
  position: relative; width: 320px;
}
.search-box input {
  width: 100%; padding: 0.5rem 1rem 0.5rem 2.5rem;
  background: var(--bg-tertiary); border: 1px solid var(--border);
  border-radius: 8px; color: var(--text-primary);
  font-size: 0.875rem; outline: none;
  transition: border-color var(--transition), box-shadow var(--transition);
}
.search-box input:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-glow);
}
.search-box .search-icon {
  position: absolute; left: 0.75rem; top: 50%; transform: translateY(-50%);
  color: var(--text-muted); font-size: 0.9rem; pointer-events: none;
}
.search-results {
  position: absolute; top: calc(100% + 6px); left: 0; right: 0;
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: var(--radius); max-height: 360px; overflow-y: auto;
  box-shadow: var(--shadow); display: none; z-index: 200;
}
.search-results.active { display: block; }
.search-result-item {
  padding: 0.75rem 1rem; cursor: pointer; border-bottom: 1px solid var(--border);
  transition: background var(--transition);
}
.search-result-item:hover { background: var(--accent-glow); }
.search-result-item:last-child { border-bottom: none; }
.search-result-item .sr-title { font-weight: 600; font-size: 0.9rem; }
.search-result-item .sr-section { font-size: 0.75rem; color: var(--text-muted); }

/* Theme Toggle */
.theme-toggle {
  background: var(--bg-tertiary); border: 1px solid var(--border);
  color: var(--text-primary); width: 40px; height: 40px;
  border-radius: 50%; cursor: pointer; font-size: 1.1rem;
  display: flex; align-items: center; justify-content: center;
  transition: all var(--transition);
}
.theme-toggle:hover { border-color: var(--accent); background: var(--accent-glow); }

/* ===== SIDEBAR ===== */
.sidebar {
  position: fixed; top: 0; left: 0; bottom: 0;
  width: var(--sidebar-width); background: var(--bg-secondary);
  border-right: 1px solid var(--border);
  overflow-y: auto; z-index: 150;
  transition: transform var(--transition), background var(--transition);
  display: flex; flex-direction: column;
}
.sidebar-brand {
  padding: 1rem 1.25rem; border-bottom: 1px solid var(--border);
  display: flex; align-items: center; gap: 0.75rem;
}
.sidebar-brand .logo {
  width: 36px; height: 36px; border-radius: 10px;
  background: linear-gradient(135deg, var(--accent), var(--accent-cyan));
  display: flex; align-items: center; justify-content: center;
  font-size: 1.1rem; font-weight: 800; color: #fff;
}
.sidebar-brand .brand-text { font-size: 1rem; font-weight: 700; }
.sidebar-brand .brand-sub { font-size: 0.7rem; color: var(--text-muted); }

/* Progress Bar */
.sidebar-progress {
  padding: 0.75rem 1.25rem; border-bottom: 1px solid var(--border);
}
.progress-label {
  font-size: 0.75rem; color: var(--text-muted); margin-bottom: 0.4rem;
  display: flex; justify-content: space-between;
}
.progress-bar {
  height: 6px; background: var(--bg-tertiary); border-radius: 3px; overflow: hidden;
}
.progress-fill {
  height: 100%; background: linear-gradient(90deg, var(--accent), var(--accent-cyan));
  border-radius: 3px; transition: width 0.5s ease; width: 0%;
}

/* Nav */
.sidebar-nav { flex: 1; padding: 0.5rem 0; overflow-y: auto; }
.nav-section { padding: 0.75rem 1.25rem 0.25rem; }
.nav-section-title {
  font-size: 0.65rem; text-transform: uppercase; letter-spacing: 1.5px;
  color: var(--text-muted); font-weight: 700;
}
.nav-item {
  display: flex; align-items: center; gap: 0.65rem;
  padding: 0.5rem 1.25rem; cursor: pointer;
  color: var(--text-secondary); font-size: 0.85rem;
  transition: all var(--transition); border-left: 3px solid transparent;
  position: relative;
}
.nav-item:hover {
  background: var(--accent-glow); color: var(--text-primary);
}
.nav-item.active {
  background: var(--accent-glow); color: var(--accent);
  border-left-color: var(--accent); font-weight: 600;
}
.nav-item .nav-icon { font-size: 1rem; width: 20px; text-align: center; }
.nav-item .nav-check {
  margin-left: auto; font-size: 0.75rem; color: var(--accent-green);
  opacity: 0; transition: opacity var(--transition);
}
.nav-item.completed .nav-check { opacity: 1; }
.nav-group-toggle {
  display: flex; align-items: center; gap: 0.65rem;
  padding: 0.5rem 1.25rem; cursor: pointer;
  color: var(--text-secondary); font-size: 0.85rem; font-weight: 600;
  transition: all var(--transition); width: 100%; border: none; background: none;
  text-align: left;
}
.nav-group-toggle:hover { background: var(--accent-glow); color: var(--text-primary); }
.nav-group-toggle .arrow {
  margin-left: auto; transition: transform var(--transition); font-size: 0.7rem;
}
.nav-group-toggle.open .arrow { transform: rotate(90deg); }
.nav-group-content { display: none; }
.nav-group-content.open { display: block; }
.nav-group-content .nav-item { padding-left: 2.5rem; font-size: 0.82rem; }

/* ===== MAIN CONTENT ===== */
.main-content {
  margin-left: var(--sidebar-width);
  margin-top: var(--header-height);
  flex: 1; min-height: calc(100vh - var(--header-height));
  padding: 2rem 2.5rem 4rem;
  max-width: 960px;
  transition: margin-left var(--transition);
}

/* ===== PAGE STYLES ===== */
.page { display: none; animation: fadeIn 0.3s ease; }
.page.active { display: block; }
@keyframes fadeIn { from { opacity: 0; transform: translateY(10px); } to { opacity: 1; transform: translateY(0); } }

.page-title {
  font-size: 2rem; margin-bottom: 0.25rem;
  background: linear-gradient(135deg, var(--accent), var(--accent-cyan));
  -webkit-background-clip: text; -webkit-text-fill-color: transparent;
  background-clip: text;
}
.page-subtitle { color: var(--text-muted); margin-bottom: 2rem; font-size: 1rem; }

/* Section Cards */
.content-section {
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 1.75rem;
  margin-bottom: 1.5rem; transition: all var(--transition);
}
.content-section:hover { border-color: rgba(108,99,255,0.3); box-shadow: 0 0 20px var(--accent-glow); }
.section-title {
  font-size: 1.3rem; margin-bottom: 1rem; display: flex;
  align-items: center; gap: 0.5rem;
}
.section-title .icon { font-size: 1.2rem; }

/* Analogy Box */
.analogy-box {
  background: linear-gradient(135deg, rgba(108,99,255,0.08), rgba(6,182,212,0.08));
  border: 1px solid rgba(108,99,255,0.2); border-radius: var(--radius);
  padding: 1.25rem; margin: 1rem 0;
}
.analogy-box .analogy-label {
  font-size: 0.75rem; text-transform: uppercase; letter-spacing: 1px;
  color: var(--accent); font-weight: 700; margin-bottom: 0.5rem;
  display: flex; align-items: center; gap: 0.4rem;
}

/* Warning/Tip/Note Boxes */
.info-box {
  border-radius: var(--radius); padding: 1rem 1.25rem; margin: 1rem 0;
  display: flex; gap: 0.75rem; align-items: flex-start;
}
.info-box .info-icon { font-size: 1.2rem; flex-shrink: 0; margin-top: 0.1rem; }
.info-box.warning {
  background: rgba(245,158,11,0.08); border: 1px solid rgba(245,158,11,0.25);
}
.info-box.warning .info-icon { color: var(--accent-orange); }
.info-box.danger {
  background: rgba(239,68,68,0.08); border: 1px solid rgba(239,68,68,0.25);
}
.info-box.danger .info-icon { color: var(--accent-red); }
.info-box.tip {
  background: rgba(34,197,94,0.08); border: 1px solid rgba(34,197,94,0.25);
}
.info-box.tip .info-icon { color: var(--accent-green); }
.info-box.note {
  background: rgba(6,182,212,0.08); border: 1px solid rgba(6,182,212,0.25);
}
.info-box.note .info-icon { color: var(--accent-cyan); }

/* Code Blocks */
.code-block {
  position: relative; background: var(--bg-code);
  border: 1px solid var(--border); border-radius: var(--radius);
  margin: 1rem 0; overflow: hidden;
}
.code-header {
  display: flex; justify-content: space-between; align-items: center;
  padding: 0.5rem 1rem; background: rgba(0,0,0,0.15);
  border-bottom: 1px solid var(--border); font-size: 0.75rem;
  color: var(--text-muted);
}
.code-header .lang { font-weight: 600; text-transform: uppercase; }
.copy-btn {
  background: var(--bg-tertiary); border: 1px solid var(--border);
  color: var(--text-secondary); padding: 0.2rem 0.6rem;
  border-radius: 4px; cursor: pointer; font-size: 0.72rem;
  transition: all var(--transition); display: flex; align-items: center; gap: 0.3rem;
}
.copy-btn:hover { background: var(--accent); color: #fff; border-color: var(--accent); }
.copy-btn.copied { background: var(--accent-green); color: #fff; border-color: var(--accent-green); }
.code-block pre {
  padding: 1rem 1.25rem; overflow-x: auto; font-family: var(--font-mono);
  font-size: 0.85rem; line-height: 1.6; color: var(--text-primary);
}
.code-block code { font-family: inherit; }
.code-inline {
  background: var(--bg-code); padding: 0.15rem 0.45rem; border-radius: 4px;
  font-family: var(--font-mono); font-size: 0.82em; border: 1px solid var(--border);
}

/* Syntax Highlighting */
.cmd { color: #7dd3fc; }
.flag { color: #c084fc; }
.path { color: #fbbf24; }
.comment { color: #6b7089; font-style: italic; }
.string { color: #86efac; }
.output { color: #94a3b8; }
.keyword { color: #f472b6; }
.num { color: #fb923c; }

/* Tabs */
.tabs { display: flex; gap: 0; margin-bottom: 0; border-bottom: 2px solid var(--border); }
.tab-btn {
  padding: 0.6rem 1.25rem; background: none; border: none;
  color: var(--text-muted); cursor: pointer; font-size: 0.85rem;
  font-weight: 500; transition: all var(--transition);
  border-bottom: 2px solid transparent; margin-bottom: -2px;
}
.tab-btn:hover { color: var(--text-primary); }
.tab-btn.active { color: var(--accent); border-bottom-color: var(--accent); }
.tab-content { display: none; padding-top: 1rem; }
.tab-content.active { display: block; }

/* Tables */
.styled-table {
  width: 100%; border-collapse: collapse; margin: 1rem 0;
  font-size: 0.88rem;
}
.styled-table th, .styled-table td {
  padding: 0.75rem 1rem; text-align: left;
  border-bottom: 1px solid var(--border);
}
.styled-table th {
  background: var(--bg-tertiary); font-weight: 700;
  font-size: 0.8rem; text-transform: uppercase; letter-spacing: 0.5px;
  color: var(--text-muted);
}
.styled-table tr:hover { background: var(--accent-glow); }

/* Accordion (Interview Q&A) */
.accordion-item {
  border: 1px solid var(--border); border-radius: var(--radius-sm);
  margin-bottom: 0.5rem; overflow: hidden;
}
.accordion-header {
  padding: 0.85rem 1rem; background: var(--bg-tertiary);
  cursor: pointer; display: flex; align-items: center; gap: 0.6rem;
  font-weight: 600; font-size: 0.9rem; transition: background var(--transition);
  border: none; width: 100%; text-align: left; color: var(--text-primary);
}
.accordion-header:hover { background: var(--accent-glow); }
.accordion-header .q-badge {
  background: var(--accent); color: #fff; font-size: 0.65rem;
  padding: 0.15rem 0.45rem; border-radius: 3px; font-weight: 700;
}
.accordion-header .arrow-acc { margin-left: auto; transition: transform var(--transition); }
.accordion-header.open .arrow-acc { transform: rotate(180deg); }
.accordion-body {
  padding: 0 1rem; max-height: 0; overflow: hidden;
  transition: max-height 0.35s ease, padding 0.35s ease;
  background: var(--bg-card);
}
.accordion-body.open { max-height: 1200px; padding: 1rem; }

/* Lab Steps */
.lab-steps { counter-reset: lab-step; list-style: none; padding: 0; }
.lab-steps li {
  counter-increment: lab-step; padding: 0.6rem 0 0.6rem 2.5rem;
  position: relative; border-left: 2px solid var(--border); margin-left: 0.75rem;
}
.lab-steps li::before {
  content: counter(lab-step);
  position: absolute; left: -13px; top: 0.55rem;
  width: 24px; height: 24px; border-radius: 50%;
  background: var(--accent); color: #fff; font-size: 0.7rem;
  font-weight: 700; display: flex; align-items: center; justify-content: center;
}

/* Home Page Cards */
.roadmap-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); gap: 1rem; }
.roadmap-card {
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 1.5rem;
  cursor: pointer; transition: all var(--transition);
  position: relative; overflow: hidden;
}
.roadmap-card::before {
  content: ''; position: absolute; top: 0; left: 0; right: 0;
  height: 3px; background: linear-gradient(90deg, var(--accent), var(--accent-cyan));
  transform: scaleX(0); transition: transform var(--transition); transform-origin: left;
}
.roadmap-card:hover { transform: translateY(-3px); box-shadow: 0 8px 30px rgba(0,0,0,0.2); border-color: rgba(108,99,255,0.3); }
.roadmap-card:hover::before { transform: scaleX(1); }
.roadmap-card .card-icon { font-size: 2rem; margin-bottom: 0.75rem; }
.roadmap-card .card-title { font-size: 1.05rem; font-weight: 700; margin-bottom: 0.4rem; }
.roadmap-card .card-desc { font-size: 0.82rem; color: var(--text-secondary); }
.roadmap-card .card-badge {
  position: absolute; top: 1rem; right: 1rem; font-size: 0.65rem;
  padding: 0.2rem 0.6rem; border-radius: 20px; font-weight: 600;
}
.badge-beginner { background: rgba(34,197,94,0.15); color: var(--accent-green); }
.badge-intermediate { background: rgba(245,158,11,0.15); color: var(--accent-orange); }
.badge-advanced { background: rgba(239,68,68,0.15); color: var(--accent-red); }

/* Hero */
.hero {
  text-align: center; padding: 3rem 0 2rem;
}
.hero h1 { font-size: 2.5rem; margin-bottom: 0.5rem; }
.hero .hero-gradient {
  background: linear-gradient(135deg, var(--accent), var(--accent-cyan), var(--accent-green));
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
}
.hero p { color: var(--text-secondary); font-size: 1.1rem; max-width: 600px; margin: 0 auto 2rem; }
.hero-stats { display: flex; justify-content: center; gap: 2.5rem; margin-top: 1.5rem; }
.hero-stat .stat-num {
  font-size: 1.75rem; font-weight: 800;
  background: linear-gradient(135deg, var(--accent), var(--accent-cyan));
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
}
.hero-stat .stat-label { font-size: 0.75rem; color: var(--text-muted); }

/* Mark Complete Button */
.mark-complete-btn {
  display: inline-flex; align-items: center; gap: 0.5rem;
  padding: 0.6rem 1.5rem; background: var(--bg-tertiary);
  border: 1px solid var(--border); border-radius: var(--radius);
  color: var(--text-secondary); cursor: pointer; font-size: 0.85rem;
  transition: all var(--transition); margin-top: 1.5rem;
}
.mark-complete-btn:hover { border-color: var(--accent-green); color: var(--accent-green); }
.mark-complete-btn.completed {
  background: rgba(34,197,94,0.1); border-color: var(--accent-green);
  color: var(--accent-green);
}

/* Scenario Cards */
.scenario-card {
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: var(--radius); overflow: hidden; margin-bottom: 1rem;
}
.scenario-header {
  padding: 1rem 1.25rem; cursor: pointer; display: flex;
  align-items: center; gap: 0.75rem; transition: background var(--transition);
  border: none; width: 100%; text-align: left; background: none; color: var(--text-primary);
  font-size: 1rem; font-weight: 600;
}
.scenario-header:hover { background: var(--accent-glow); }
.scenario-header .scenario-icon { font-size: 1.5rem; }
.scenario-header .arrow-sc { margin-left: auto; transition: transform var(--transition); }
.scenario-header.open .arrow-sc { transform: rotate(180deg); }
.scenario-body {
  max-height: 0; overflow: hidden; transition: max-height 0.4s ease;
}
.scenario-body.open { max-height: 5000px; }
.scenario-body-inner { padding: 1.25rem; border-top: 1px solid var(--border); }

/* Scrollbar */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--text-muted); }

/* ===== RESPONSIVE ===== */
@media (max-width: 768px) {
  .sidebar { transform: translateX(-100%); }
  .sidebar.open { transform: translateX(0); }
  .header { left: 0; }
  .main-content { margin-left: 0; padding: 1.5rem 1rem; }
  .hamburger { display: block; }
  .search-box { width: 180px; }
  .hero h1 { font-size: 1.75rem; }
  .hero-stats { gap: 1.5rem; }
  .roadmap-grid { grid-template-columns: 1fr; }
}

/* Overlay for mobile sidebar */
.sidebar-overlay {
  display: none; position: fixed; inset: 0;
  background: rgba(0,0,0,0.5); z-index: 140;
}
.sidebar-overlay.active { display: block; }