/* ========================================
   JAVA LEARNING GUIDE - STYLESHEET
   Modern, Minimalist & Elegant Design
   ======================================== */

/* === Google Fonts Import === */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800;900&family=JetBrains+Mono:wght@400;500;600;700&family=Outfit:wght@300;400;500;600;700;800&display=swap');

/* === CSS Custom Properties === */
:root {
  /* Primary Palette */
  --java-orange: #F89820;
  --java-orange-light: #FFB347;
  --java-orange-glow: rgba(248, 152, 32, 0.15);
  --java-blue: #5382A1;
  --java-blue-light: #6B9CC4;
  --java-red: #E76F51;

  /* Backgrounds */
  --bg-primary: #0A0A0F;
  --bg-secondary: #12121A;
  --bg-tertiary: #1A1A25;
  --bg-card: rgba(22, 22, 35, 0.7);
  --bg-card-hover: rgba(30, 30, 48, 0.85);
  --bg-code: #0D1117;
  --bg-code-header: #161B22;
  --bg-inline-code: rgba(248, 152, 32, 0.08);

  /* Text */
  --text-primary: #E8E8ED;
  --text-secondary: #9898A6;
  --text-muted: #6B6B7B;
  --text-accent: #F89820;
  --text-code: #C9D1D9;

  /* Borders */
  --border-subtle: rgba(255, 255, 255, 0.06);
  --border-medium: rgba(255, 255, 255, 0.1);
  --border-accent: rgba(248, 152, 32, 0.3);

  /* Gradients */
  --gradient-hero: linear-gradient(135deg, #F89820 0%, #E76F51 50%, #5382A1 100%);
  --gradient-card: linear-gradient(145deg, rgba(248, 152, 32, 0.05) 0%, rgba(83, 130, 161, 0.05) 100%);
  --gradient-section: linear-gradient(180deg, transparent 0%, rgba(248, 152, 32, 0.02) 50%, transparent 100%);

  /* Shadows */
  --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 20px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 8px 40px rgba(0, 0, 0, 0.5);
  --shadow-glow: 0 0 30px rgba(248, 152, 32, 0.1);
  --shadow-code: 0 4px 24px rgba(0, 0, 0, 0.6);

  /* Spacing */
  --section-gap: 5rem;
  --content-max: 900px;
  --sidebar-width: 280px;

  /* Transitions */
  --ease-smooth: cubic-bezier(0.4, 0, 0.2, 1);
  --ease-bounce: cubic-bezier(0.34, 1.56, 0.64, 1);

  /* Code Syntax Colors */
  --syntax-keyword: #FF7B72;
  --syntax-string: #A5D6FF;
  --syntax-number: #79C0FF;
  --syntax-comment: #8B949E;
  --syntax-type: #FFA657;
  --syntax-method: #D2A8FF;
  --syntax-variable: #C9D1D9;
  --syntax-annotation: #7EE787;
  --syntax-operator: #FF7B72;
}

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: 80px;
  font-size: 16px;
}

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.7;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* === Background Ambient Effects === */
body::before {
  content: '';
  position: fixed;
  top: -50%;
  left: -50%;
  width: 200%;
  height: 200%;
  background: radial-gradient(circle at 20% 20%, rgba(248, 152, 32, 0.03) 0%, transparent 50%),
              radial-gradient(circle at 80% 80%, rgba(83, 130, 161, 0.03) 0%, transparent 50%),
              radial-gradient(circle at 50% 50%, rgba(231, 111, 81, 0.02) 0%, transparent 50%);
  z-index: -1;
  animation: ambientFloat 20s ease-in-out infinite;
}

@keyframes ambientFloat {
  0%, 100% { transform: translate(0, 0) rotate(0deg); }
  33% { transform: translate(2%, -2%) rotate(1deg); }
  66% { transform: translate(-1%, 1%) rotate(-1deg); }
}

/* === Selection Style === */
::selection {
  background: rgba(248, 152, 32, 0.3);
  color: #fff;
}

/* === Scrollbar === */
::-webkit-scrollbar {
  width: 6px;
}

::-webkit-scrollbar-track {
  background: var(--bg-primary);
}

::-webkit-scrollbar-thumb {
  background: rgba(248, 152, 32, 0.3);
  border-radius: 3px;
}

::-webkit-scrollbar-thumb:hover {
  background: rgba(248, 152, 32, 0.5);
}

/* === Typography === */
h1, h2, h3, h4, h5, h6 {
  font-family: 'Outfit', sans-serif;
  line-height: 1.2;
  letter-spacing: -0.02em;
}

/* ========================================
   NAVIGATION - Fixed Sidebar
   ======================================== */
.sidebar {
  position: fixed;
  top: 0;
  left: 0;
  width: var(--sidebar-width);
  height: 100vh;
  background: rgba(12, 12, 20, 0.95);
  backdrop-filter: blur(20px);
  border-right: 1px solid var(--border-subtle);
  z-index: 1000;
  overflow-y: auto;
  padding: 2rem 0;
  transition: transform 0.4s var(--ease-smooth);
}

.sidebar::-webkit-scrollbar {
  width: 3px;
}

.sidebar::-webkit-scrollbar-thumb {
  background: rgba(248, 152, 32, 0.2);
  border-radius: 3px;
}

.sidebar-logo {
  padding: 0 1.5rem 1.5rem;
  border-bottom: 1px solid var(--border-subtle);
  margin-bottom: 1rem;
}

.sidebar-logo .logo-text {
  font-family: 'Outfit', sans-serif;
  font-size: 1.4rem;
  font-weight: 700;
  background: var(--gradient-hero);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

.sidebar-logo .logo-text .logo-icon {
  font-size: 1.6rem;
  -webkit-text-fill-color: initial;
}

.sidebar-logo .logo-subtitle {
  font-size: 0.75rem;
  color: var(--text-muted);
  margin-top: 0.25rem;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.nav-section {
  padding: 0.5rem 1rem;
}

.nav-section-title {
  font-family: 'Outfit', sans-serif;
  font-size: 0.65rem;
  font-weight: 700;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  padding: 0.5rem 0.75rem;
  margin-top: 0.5rem;
}

.nav-link {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  padding: 0.55rem 0.75rem;
  color: var(--text-secondary);
  text-decoration: none;
  font-size: 0.85rem;
  font-weight: 400;
  border-radius: 8px;
  transition: all 0.25s var(--ease-smooth);
  position: relative;
}

.nav-link:hover {
  color: var(--text-primary);
  background: rgba(248, 152, 32, 0.06);
}

.nav-link.active {
  color: var(--java-orange);
  background: rgba(248, 152, 32, 0.1);
  font-weight: 500;
}

.nav-link.active::before {
  content: '';
  position: absolute;
  left: 0;
  top: 50%;
  transform: translateY(-50%);
  width: 3px;
  height: 60%;
  background: var(--java-orange);
  border-radius: 0 3px 3px 0;
}

.nav-link .nav-icon {
  font-size: 1rem;
  width: 1.2rem;
  text-align: center;
  flex-shrink: 0;
}

.nav-link .nav-number {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.65rem;
  color: var(--text-muted);
  margin-left: auto;
  opacity: 0.5;
}

/* Mobile sidebar toggle */
.sidebar-toggle {
  display: none;
  position: fixed;
  top: 1rem;
  left: 1rem;
  z-index: 1001;
  width: 44px;
  height: 44px;
  border-radius: 12px;
  background: rgba(12, 12, 20, 0.9);
  backdrop-filter: blur(10px);
  border: 1px solid var(--border-medium);
  color: var(--text-primary);
  font-size: 1.2rem;
  cursor: pointer;
  align-items: center;
  justify-content: center;
  transition: all 0.3s var(--ease-smooth);
}

.sidebar-toggle:hover {
  background: rgba(248, 152, 32, 0.15);
  border-color: var(--border-accent);
}

/* ========================================
   MAIN CONTENT
   ======================================== */
.main-content {
  margin-left: var(--sidebar-width);
  min-height: 100vh;
}

/* ========================================
   HERO SECTION
   ======================================== */
.hero {
  position: relative;
  padding: 6rem 3rem 4rem;
  overflow: hidden;
  border-bottom: 1px solid var(--border-subtle);
}

.hero::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: radial-gradient(ellipse at 30% 50%, rgba(248, 152, 32, 0.08) 0%, transparent 60%),
              radial-gradient(ellipse at 70% 30%, rgba(83, 130, 161, 0.06) 0%, transparent 50%);
  z-index: 0;
}

.hero-content {
  position: relative;
  z-index: 1;
  max-width: var(--content-max);
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.4rem 1rem;
  background: rgba(248, 152, 32, 0.1);
  border: 1px solid rgba(248, 152, 32, 0.2);
  border-radius: 100px;
  font-size: 0.8rem;
  font-weight: 500;
  color: var(--java-orange);
  margin-bottom: 1.5rem;
  animation: fadeInUp 0.6s var(--ease-smooth);
}

.hero-badge .pulse {
  width: 6px;
  height: 6px;
  background: var(--java-orange);
  border-radius: 50%;
  animation: pulse 2s ease-in-out infinite;
}

@keyframes pulse {
  0%, 100% { opacity: 1; transform: scale(1); }
  50% { opacity: 0.5; transform: scale(1.5); }
}

.hero h1 {
  font-size: clamp(2.5rem, 5vw, 3.8rem);
  font-weight: 800;
  margin-bottom: 1rem;
  animation: fadeInUp 0.6s var(--ease-smooth) 0.1s both;
}

.hero h1 .gradient-text {
  background: var(--gradient-hero);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-description {
  font-size: 1.1rem;
  color: var(--text-secondary);
  max-width: 600px;
  line-height: 1.8;
  animation: fadeInUp 0.6s var(--ease-smooth) 0.2s both;
}

.hero-stats {
  display: flex;
  gap: 2.5rem;
  margin-top: 2.5rem;
  animation: fadeInUp 0.6s var(--ease-smooth) 0.3s both;
}

.hero-stat {
  text-align: left;
}

.hero-stat .stat-value {
  font-family: 'Outfit', sans-serif;
  font-size: 1.8rem;
  font-weight: 700;
  color: var(--text-primary);
}

.hero-stat .stat-value .accent {
  color: var(--java-orange);
}

.hero-stat .stat-label {
  font-size: 0.8rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-top: 0.15rem;
}

/* Floating decoration */
.hero-decoration {
  position: absolute;
  right: 3rem;
  top: 50%;
  transform: translateY(-50%);
  font-size: 10rem;
  opacity: 0.04;
  font-family: 'Outfit', sans-serif;
  font-weight: 900;
  color: var(--java-orange);
  user-select: none;
  pointer-events: none;
}

@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* ========================================
   SECTIONS
   ======================================== */
.section {
  padding: var(--section-gap) 3rem;
  border-bottom: 1px solid var(--border-subtle);
  position: relative;
}

.section:last-child {
  border-bottom: none;
}

.section-inner {
  max-width: var(--content-max);
}

/* Section Header */
.section-header {
  margin-bottom: 2.5rem;
}

.section-number {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--java-orange);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.5rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.section-number::after {
  content: '';
  width: 30px;
  height: 1px;
  background: var(--java-orange);
  opacity: 0.4;
}

.section-title {
  font-size: clamp(1.8rem, 3vw, 2.4rem);
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 0.75rem;
}

.section-subtitle {
  font-size: 1rem;
  color: var(--text-secondary);
  max-width: 650px;
  line-height: 1.7;
}

/* ========================================
   CONTENT ELEMENTS
   ======================================== */

/* Text Content */
.content-text {
  font-size: 1rem;
  color: var(--text-secondary);
  line-height: 1.8;
  margin-bottom: 1.5rem;
}

.content-text strong {
  color: var(--text-primary);
  font-weight: 600;
}

.content-text em {
  color: var(--java-orange-light);
  font-style: normal;
  font-weight: 500;
}

/* Inline Code */
.inline-code, code:not([class]) {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.85em;
  padding: 0.15em 0.5em;
  background: var(--bg-inline-code);
  border: 1px solid rgba(248, 152, 32, 0.15);
  border-radius: 5px;
  color: var(--java-orange-light);
  font-weight: 500;
}

/* ========================================
   CODE BLOCKS
   ======================================== */
.code-block {
  margin: 1.5rem 0;
  border-radius: 12px;
  overflow: hidden;
  border: 1px solid var(--border-subtle);
  box-shadow: var(--shadow-code);
  transition: all 0.3s var(--ease-smooth);
}

.code-block:hover {
  border-color: rgba(248, 152, 32, 0.15);
  box-shadow: var(--shadow-code), var(--shadow-glow);
}

.code-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.65rem 1rem;
  background: var(--bg-code-header);
  border-bottom: 1px solid var(--border-subtle);
}

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

.code-dots {
  display: flex;
  gap: 6px;
}

.code-dots span {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  opacity: 0.7;
}

.code-dots span:nth-child(1) { background: #FF5F57; }
.code-dots span:nth-child(2) { background: #FEBC2E; }
.code-dots span:nth-child(3) { background: #28C840; }

.code-filename {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.75rem;
  color: var(--text-muted);
  font-weight: 500;
}

.code-copy-btn {
  background: none;
  border: 1px solid var(--border-subtle);
  color: var(--text-muted);
  font-family: 'Inter', sans-serif;
  font-size: 0.7rem;
  padding: 0.3rem 0.7rem;
  border-radius: 6px;
  cursor: pointer;
  transition: all 0.25s var(--ease-smooth);
  display: flex;
  align-items: center;
  gap: 0.3rem;
}

.code-copy-btn:hover {
  color: var(--java-orange);
  border-color: var(--border-accent);
  background: rgba(248, 152, 32, 0.05);
}

.code-copy-btn.copied {
  color: #28C840;
  border-color: rgba(40, 200, 64, 0.3);
}

.code-body {
  background: var(--bg-code);
  padding: 1.25rem 1.5rem;
  overflow-x: auto;
}

.code-body pre {
  margin: 0;
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.85rem;
  line-height: 1.7;
  color: var(--text-code);
  tab-size: 4;
}

.code-body pre code {
  background: none;
  border: none;
  padding: 0;
  font-size: inherit;
  color: inherit;
}

/* Syntax Highlighting */
.kw { color: var(--syntax-keyword); font-weight: 500; }
.str { color: var(--syntax-string); }
.num { color: var(--syntax-number); }
.cmt { color: var(--syntax-comment); font-style: italic; }
.typ { color: var(--syntax-type); }
.mth { color: var(--syntax-method); }
.var { color: var(--syntax-variable); }
.ann { color: var(--syntax-annotation); }
.op { color: var(--syntax-operator); }

/* ========================================
   INFO CARDS & CALLOUTS
   ======================================== */
.info-card {
  padding: 1.25rem 1.5rem;
  border-radius: 12px;
  border-left: 3px solid;
  margin: 1.5rem 0;
  position: relative;
  transition: all 0.3s var(--ease-smooth);
}

.info-card:hover {
  transform: translateX(4px);
}

.info-card.tip {
  background: rgba(40, 200, 64, 0.05);
  border-color: #28C840;
}

.info-card.warning {
  background: rgba(254, 188, 46, 0.05);
  border-color: #FEBC2E;
}

.info-card.important {
  background: rgba(248, 152, 32, 0.05);
  border-color: var(--java-orange);
}

.info-card.note {
  background: rgba(83, 130, 161, 0.05);
  border-color: var(--java-blue);
}

.info-card-title {
  font-family: 'Outfit', sans-serif;
  font-size: 0.85rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.5rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.info-card.tip .info-card-title { color: #28C840; }
.info-card.warning .info-card-title { color: #FEBC2E; }
.info-card.important .info-card-title { color: var(--java-orange); }
.info-card.note .info-card-title { color: var(--java-blue-light); }

.info-card p {
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.7;
}

/* ========================================
   CONCEPT CARDS
   ======================================== */
.concept-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: 1rem;
  margin: 1.5rem 0;
}

.concept-card {
  padding: 1.5rem;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: 12px;
  transition: all 0.35s var(--ease-smooth);
  position: relative;
  overflow: hidden;
}

.concept-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: var(--gradient-hero);
  opacity: 0;
  transition: opacity 0.35s var(--ease-smooth);
}

.concept-card:hover {
  background: var(--bg-card-hover);
  border-color: var(--border-medium);
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
}

.concept-card:hover::before {
  opacity: 1;
}

.concept-card .card-icon {
  font-size: 1.8rem;
  margin-bottom: 0.75rem;
}

.concept-card h4 {
  font-family: 'Outfit', sans-serif;
  font-size: 1rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 0.5rem;
}

.concept-card p {
  font-size: 0.85rem;
  color: var(--text-secondary);
  line-height: 1.6;
}

/* ========================================
   DATA TABLES
   ======================================== */
.table-wrapper {
  margin: 1.5rem 0;
  border-radius: 12px;
  overflow: hidden;
  border: 1px solid var(--border-subtle);
}

.data-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.9rem;
}

.data-table thead {
  background: var(--bg-code-header);
}

.data-table th {
  font-family: 'Outfit', sans-serif;
  font-weight: 600;
  font-size: 0.8rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: 0.85rem 1.25rem;
  text-align: left;
  border-bottom: 1px solid var(--border-subtle);
}

.data-table td {
  padding: 0.75rem 1.25rem;
  border-bottom: 1px solid var(--border-subtle);
  color: var(--text-secondary);
}

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

.data-table tr:hover td {
  background: rgba(248, 152, 32, 0.03);
}

.data-table td:first-child {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.85rem;
  color: var(--java-orange-light);
  font-weight: 500;
}

.data-table tbody tr {
  transition: background 0.2s var(--ease-smooth);
}

/* ========================================
   STEP BY STEP
   ======================================== */
.steps {
  margin: 1.5rem 0;
  position: relative;
}

.step {
  display: flex;
  gap: 1.25rem;
  margin-bottom: 1.5rem;
  position: relative;
}

.step-indicator {
  flex-shrink: 0;
  width: 36px;
  height: 36px;
  border-radius: 10px;
  background: rgba(248, 152, 32, 0.1);
  border: 1px solid rgba(248, 152, 32, 0.2);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--java-orange);
  position: relative;
  z-index: 1;
}

.step:not(:last-child) .step-indicator::after {
  content: '';
  position: absolute;
  top: 100%;
  left: 50%;
  transform: translateX(-50%);
  width: 1px;
  height: calc(100% + 0.75rem);
  background: rgba(248, 152, 32, 0.15);
}

.step-content {
  flex: 1;
  padding-top: 0.3rem;
}

.step-content h4 {
  font-family: 'Outfit', sans-serif;
  font-size: 1rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 0.35rem;
}

.step-content p {
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.7;
}

/* ========================================
   LISTS
   ======================================== */
.feature-list {
  list-style: none;
  margin: 1rem 0;
}

.feature-list li {
  padding: 0.5rem 0;
  padding-left: 1.5rem;
  position: relative;
  color: var(--text-secondary);
  font-size: 0.95rem;
  line-height: 1.7;
}

.feature-list li::before {
  content: '▸';
  position: absolute;
  left: 0;
  color: var(--java-orange);
  font-weight: 700;
}

.feature-list li strong {
  color: var(--text-primary);
  font-weight: 600;
}

/* ========================================
   COMPARISON / DUAL PANEL
   ======================================== */
.comparison-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
  margin: 1.5rem 0;
}

.comparison-panel {
  padding: 1.25rem;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: 12px;
}

.comparison-panel h4 {
  font-family: 'Outfit', sans-serif;
  font-size: 0.9rem;
  font-weight: 600;
  margin-bottom: 0.75rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.panel-good h4 { color: #28C840; }
.panel-bad h4 { color: var(--java-red); }

/* ========================================
   OUTPUT / CONSOLE BLOCK
   ======================================== */
.output-block {
  margin: 1rem 0;
  border-radius: 10px;
  overflow: hidden;
  border: 1px solid rgba(40, 200, 64, 0.15);
}

.output-header {
  padding: 0.5rem 1rem;
  background: rgba(40, 200, 64, 0.08);
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.7rem;
  font-weight: 600;
  color: #28C840;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.output-body {
  padding: 1rem 1.25rem;
  background: rgba(13, 17, 23, 0.8);
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.85rem;
  color: #28C840;
  line-height: 1.6;
}

/* ========================================
   DIVIDER
   ======================================== */
.section-divider {
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--border-medium), transparent);
  margin: 1.5rem 0;
  border: none;
}

/* ========================================
   BACK TO TOP
   ======================================== */
.back-to-top {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  width: 44px;
  height: 44px;
  border-radius: 12px;
  background: rgba(248, 152, 32, 0.15);
  backdrop-filter: blur(10px);
  border: 1px solid rgba(248, 152, 32, 0.25);
  color: var(--java-orange);
  font-size: 1.1rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.3s var(--ease-smooth);
  opacity: 0;
  pointer-events: none;
  z-index: 999;
}

.back-to-top.visible {
  opacity: 1;
  pointer-events: all;
}

.back-to-top:hover {
  background: rgba(248, 152, 32, 0.25);
  transform: translateY(-3px);
}

/* ========================================
   FOOTER
   ======================================== */
.footer {
  padding: 3rem;
  text-align: center;
  border-top: 1px solid var(--border-subtle);
}

.footer p {
  font-size: 0.85rem;
  color: var(--text-muted);
}

.footer .footer-heart {
  color: var(--java-red);
}

.footer .footer-java {
  color: var(--java-orange);
  font-weight: 600;
}

/* ========================================
   SUBSECTION
   ======================================== */
.subsection {
  margin: 2.5rem 0;
}

.subsection-title {
  font-family: 'Outfit', sans-serif;
  font-size: 1.3rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 1rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.subsection-title .sub-icon {
  font-size: 1.1rem;
}

/* ========================================
   PROGRESS BAR (VISUAL INDICATOR)
   ======================================== */
.progress-indicator {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin: 1rem 0;
}

.progress-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--border-medium);
  transition: all 0.3s var(--ease-smooth);
}

.progress-dot.active {
  background: var(--java-orange);
  box-shadow: 0 0 8px rgba(248, 152, 32, 0.4);
}

.progress-label {
  font-size: 0.75rem;
  color: var(--text-muted);
  font-family: 'JetBrains Mono', monospace;
}

/* ========================================
   ANIMATIONS
   ======================================== */
.fade-in {
  opacity: 0;
  transform: translateY(20px);
  transition: all 0.6s var(--ease-smooth);
}

.fade-in.visible {
  opacity: 1;
  transform: translateY(0);
}

/* ========================================
   RESPONSIVE DESIGN
   ======================================== */
@media (max-width: 1024px) {
  .sidebar {
    transform: translateX(-100%);
  }

  .sidebar.open {
    transform: translateX(0);
  }

  .sidebar-toggle {
    display: flex;
  }

  .main-content {
    margin-left: 0;
  }

  .hero {
    padding: 5rem 2rem 3rem;
  }

  .section {
    padding: var(--section-gap) 2rem;
  }

  .hero-decoration {
    display: none;
  }

  .comparison-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 640px) {
  html {
    font-size: 15px;
  }

  .hero {
    padding: 4.5rem 1.25rem 2.5rem;
  }

  .section {
    padding: 3.5rem 1.25rem;
  }

  .hero-stats {
    flex-wrap: wrap;
    gap: 1.5rem;
  }

  .concept-grid {
    grid-template-columns: 1fr;
  }

  .code-body {
    padding: 1rem;
  }

  .code-body pre {
    font-size: 0.78rem;
  }

  .footer {
    padding: 2rem 1.25rem;
  }
}

/* Sidebar overlay for mobile */
.sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  z-index: 999;
  opacity: 0;
  transition: opacity 0.3s var(--ease-smooth);
}

.sidebar-overlay.active {
  display: block;
  opacity: 1;
}

/* ========================================
   TOPIC BADGE / TAG
   ======================================== */
.topic-tag {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  padding: 0.2rem 0.65rem;
  background: rgba(248, 152, 32, 0.08);
  border: 1px solid rgba(248, 152, 32, 0.15);
  border-radius: 6px;
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.72rem;
  font-weight: 500;
  color: var(--java-orange-light);
}

/* ========================================
   VISUAL DIAGRAM / FLOW
   ======================================== */
.flow-diagram {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin: 1.5rem 0;
  padding: 1.25rem;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: 12px;
  overflow-x: auto;
  flex-wrap: wrap;
  justify-content: center;
}

.flow-step {
  padding: 0.6rem 1.1rem;
  background: rgba(248, 152, 32, 0.08);
  border: 1px solid rgba(248, 152, 32, 0.15);
  border-radius: 8px;
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.8rem;
  color: var(--text-primary);
  white-space: nowrap;
  text-align: center;
}

.flow-arrow {
  color: var(--text-muted);
  font-size: 1rem;
}

/* ========================================
   ACCORDION / EXPANDABLE
   ======================================== */
.accordion {
  margin: 1.5rem 0;
}

.accordion-item {
  border: 1px solid var(--border-subtle);
  border-radius: 10px;
  margin-bottom: 0.5rem;
  overflow: hidden;
  transition: all 0.3s var(--ease-smooth);
}

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

.accordion-header {
  width: 100%;
  padding: 1rem 1.25rem;
  background: var(--bg-card);
  border: none;
  color: var(--text-primary);
  font-family: 'Inter', sans-serif;
  font-size: 0.95rem;
  font-weight: 500;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  text-align: left;
  transition: background 0.3s var(--ease-smooth);
}

.accordion-header:hover {
  background: var(--bg-card-hover);
}

.accordion-header .accordion-icon {
  font-size: 0.8rem;
  transition: transform 0.3s var(--ease-smooth);
  color: var(--java-orange);
}

.accordion-item.open .accordion-icon {
  transform: rotate(90deg);
}

.accordion-body {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.4s var(--ease-smooth);
}

.accordion-item.open .accordion-body {
  max-height: 2000px;
}

.accordion-body-inner {
  padding: 0 1.25rem 1.25rem;
  background: var(--bg-card);
}

/* ========================================
   QUIZ / EXERCISE BLOCK
   ======================================== */
.exercise-block {
  margin: 2rem 0;
  padding: 1.5rem;
  background: var(--gradient-card);
  border: 1px solid rgba(248, 152, 32, 0.15);
  border-radius: 12px;
  position: relative;
}

.exercise-block::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: var(--gradient-hero);
  border-radius: 12px 12px 0 0;
}

.exercise-label {
  font-family: 'Outfit', sans-serif;
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--java-orange);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.75rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.exercise-block h4 {
  font-family: 'Outfit', sans-serif;
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 0.5rem;
}

.exercise-block p {
  font-size: 0.9rem;
  color: var(--text-secondary);
  line-height: 1.7;
}