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

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

:root {
  --bg-primary: #0a0e1a;
  --bg-secondary: #111827;
  --bg-card: #1a1f35;
  --bg-card-hover: #222845;
  --accent-blue: #3b82f6;
  --accent-cyan: #06b6d4;
  --accent-purple: #8b5cf6;
  --accent-pink: #ec4899;
  --accent-green: #10b981;
  --accent-orange: #f59e0b;
  --text-primary: #f1f5f9;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;
  --border: #1e293b;
  --glow-blue: rgba(59, 130, 246, 0.3);
  --glow-purple: rgba(139, 92, 246, 0.3);
}

html { scroll-behavior: smooth; }

body {
  font-family: 'Inter', sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.7;
  overflow-x: hidden;
}

/* === HERO === */
.hero {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 2rem;
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  width: 600px; height: 600px;
  background: radial-gradient(circle, var(--glow-blue), transparent 70%);
  top: -100px; left: -100px;
  animation: float 8s ease-in-out infinite;
}

.hero::after {
  content: '';
  position: absolute;
  width: 500px; height: 500px;
  background: radial-gradient(circle, var(--glow-purple), transparent 70%);
  bottom: -100px; right: -100px;
  animation: float 8s ease-in-out infinite reverse;
}

@keyframes float {
  0%, 100% { transform: translate(0, 0); }
  50% { transform: translate(30px, -30px); }
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.5rem 1.2rem;
  background: rgba(59, 130, 246, 0.1);
  border: 1px solid rgba(59, 130, 246, 0.3);
  border-radius: 50px;
  font-size: 0.85rem;
  color: var(--accent-blue);
  margin-bottom: 1.5rem;
  z-index: 1;
}

.hero h1 {
  font-size: clamp(2.5rem, 6vw, 4.5rem);
  font-weight: 900;
  line-height: 1.1;
  z-index: 1;
  background: linear-gradient(135deg, #fff 0%, var(--accent-blue) 50%, var(--accent-purple) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: 1.5rem;
}

.hero p {
  font-size: 1.15rem;
  color: var(--text-secondary);
  max-width: 600px;
  z-index: 1;
  margin-bottom: 2rem;
}

.hero-cta {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.9rem 2rem;
  background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
  color: #fff;
  text-decoration: none;
  border-radius: 12px;
  font-weight: 600;
  font-size: 1rem;
  z-index: 1;
  transition: transform 0.3s, box-shadow 0.3s;
}

.hero-cta:hover {
  transform: translateY(-2px);
  box-shadow: 0 10px 40px rgba(59, 130, 246, 0.4);
}

/* === NAV === */
.sticky-nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(10, 14, 26, 0.85);
  backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border);
  padding: 0.8rem 2rem;
  display: flex;
  gap: 0.5rem;
  justify-content: center;
  flex-wrap: wrap;
}

.sticky-nav a {
  padding: 0.5rem 1rem;
  color: var(--text-secondary);
  text-decoration: none;
  border-radius: 8px;
  font-size: 0.85rem;
  font-weight: 500;
  transition: all 0.3s;
}

.sticky-nav a:hover, .sticky-nav a.active {
  color: var(--accent-blue);
  background: rgba(59, 130, 246, 0.1);
}

/* === SECTIONS === */
.section {
  max-width: 900px;
  margin: 0 auto;
  padding: 5rem 2rem;
}

.section-label {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 2px;
  color: var(--accent-cyan);
  margin-bottom: 0.8rem;
}

.section h2 {
  font-size: clamp(1.8rem, 4vw, 2.5rem);
  font-weight: 800;
  margin-bottom: 1rem;
  background: linear-gradient(135deg, #fff, var(--accent-cyan));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.section > p {
  color: var(--text-secondary);
  font-size: 1.05rem;
  margin-bottom: 2rem;
}

/* === CARDS === */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: 1.5rem;
  margin-top: 2rem;
}

.card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 1.8rem;
  transition: all 0.4s;
  position: relative;
  overflow: hidden;
}

.card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--accent-blue), var(--accent-purple));
  opacity: 0;
  transition: opacity 0.4s;
}

.card:hover {
  transform: translateY(-4px);
  border-color: rgba(59, 130, 246, 0.3);
  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
}

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

.card-icon {
  width: 50px; height: 50px;
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  margin-bottom: 1rem;
}

.card-icon.blue { background: rgba(59, 130, 246, 0.15); }
.card-icon.cyan { background: rgba(6, 182, 212, 0.15); }
.card-icon.purple { background: rgba(139, 92, 246, 0.15); }
.card-icon.pink { background: rgba(236, 72, 153, 0.15); }
.card-icon.green { background: rgba(16, 185, 129, 0.15); }
.card-icon.orange { background: rgba(245, 158, 11, 0.15); }

.card h3 {
  font-size: 1.15rem;
  font-weight: 700;
  margin-bottom: 0.5rem;
}

.card p {
  color: var(--text-secondary);
  font-size: 0.9rem;
  line-height: 1.6;
}

/* === INFO BOX === */
.info-box {
  background: linear-gradient(135deg, rgba(59, 130, 246, 0.08), rgba(139, 92, 246, 0.08));
  border: 1px solid rgba(59, 130, 246, 0.2);
  border-radius: 16px;
  padding: 2rem;
  margin: 2rem 0;
}

.info-box h3 {
  font-size: 1.2rem;
  margin-bottom: 1rem;
  color: var(--accent-blue);
}

.info-box p, .info-box li {
  color: var(--text-secondary);
  font-size: 0.95rem;
}

.info-box ul {
  list-style: none;
  padding: 0;
}

.info-box li {
  padding: 0.4rem 0;
  padding-left: 1.5rem;
  position: relative;
}

.info-box li::before {
  content: '▸';
  position: absolute;
  left: 0;
  color: var(--accent-blue);
}

/* === DIAGRAM === */
.diagram {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 2rem;
  margin: 2rem 0;
  text-align: center;
  overflow-x: auto;
}

.diagram-title {
  font-weight: 700;
  margin-bottom: 1.5rem;
  color: var(--accent-cyan);
}

.osi-layers {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  max-width: 500px;
  margin: 0 auto;
}

.osi-layer {
  display: flex;
  align-items: center;
  gap: 1rem;
  padding: 0.8rem 1.2rem;
  border-radius: 10px;
  transition: all 0.3s;
  cursor: pointer;
  border: 1px solid transparent;
}

.osi-layer:hover {
  transform: scale(1.03);
  border-color: rgba(255,255,255,0.1);
}

.osi-layer .num {
  font-family: 'JetBrains Mono', monospace;
  font-weight: 700;
  font-size: 1.1rem;
  width: 30px;
}

.osi-layer .name {
  font-weight: 600;
  flex: 1;
  text-align: left;
}

.osi-layer .proto {
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.75rem;
  color: var(--text-muted);
  text-align: right;
}

/* Layer colors */
.layer-7 { background: rgba(236, 72, 153, 0.12); }
.layer-6 { background: rgba(139, 92, 246, 0.12); }
.layer-5 { background: rgba(59, 130, 246, 0.12); }
.layer-4 { background: rgba(6, 182, 212, 0.12); }
.layer-3 { background: rgba(16, 185, 129, 0.12); }
.layer-2 { background: rgba(245, 158, 11, 0.12); }
.layer-1 { background: rgba(239, 68, 68, 0.12); }

/* === CODE BLOCK === */
.code-block {
  background: #0d1117;
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1.5rem;
  margin: 1.5rem 0;
  font-family: 'JetBrains Mono', monospace;
  font-size: 0.85rem;
  color: var(--accent-green);
  overflow-x: auto;
  line-height: 1.8;
}

.code-block .comment { color: var(--text-muted); }
.code-block .keyword { color: var(--accent-purple); }
.code-block .value { color: var(--accent-orange); }

/* === NETWORK ANIMATION === */
.network-visual {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 1rem;
  flex-wrap: wrap;
  padding: 2rem;
  margin: 2rem 0;
}

.device {
  width: 80px; height: 80px;
  border-radius: 16px;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  font-size: 1.8rem;
  background: var(--bg-card);
  border: 1px solid var(--border);
  position: relative;
  transition: all 0.3s;
}

.device:hover {
  transform: scale(1.1);
  box-shadow: 0 0 30px var(--glow-blue);
}

.device span {
  font-size: 0.65rem;
  color: var(--text-muted);
  margin-top: 0.3rem;
}

.connection {
  width: 60px;
  height: 3px;
  background: linear-gradient(90deg, var(--accent-blue), var(--accent-cyan));
  position: relative;
  border-radius: 3px;
}

.connection::after {
  content: '';
  position: absolute;
  width: 10px; height: 10px;
  background: var(--accent-cyan);
  border-radius: 50%;
  top: -3.5px;
  animation: packet 1.5s linear infinite;
  box-shadow: 0 0 10px var(--accent-cyan);
}

@keyframes packet {
  0% { left: 0; }
  100% { left: calc(100% - 10px); }
}

/* === ACCORDION === */
.accordion { margin: 2rem 0; }

.accordion-item {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 12px;
  margin-bottom: 0.8rem;
  overflow: hidden;
  transition: all 0.3s;
}

.accordion-item:hover { border-color: rgba(59, 130, 246, 0.2); }

.accordion-header {
  padding: 1.2rem 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  cursor: pointer;
  font-weight: 600;
  transition: background 0.3s;
}

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

.accordion-header .arrow {
  transition: transform 0.3s;
  color: var(--text-muted);
}

.accordion-item.open .arrow { transform: rotate(180deg); }

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

.accordion-body-inner {
  padding: 0 1.5rem 1.5rem;
  color: var(--text-secondary);
  font-size: 0.9rem;
  line-height: 1.8;
}

/* === STEP LIST === */
.steps {
  counter-reset: step;
  margin: 2rem 0;
}

.step {
  counter-increment: step;
  display: flex;
  gap: 1.5rem;
  padding: 1.5rem 0;
  border-bottom: 1px solid var(--border);
}

.step::before {
  content: counter(step);
  min-width: 40px; height: 40px;
  background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
  border-radius: 10px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 1rem;
}

.step h4 {
  font-size: 1.05rem;
  margin-bottom: 0.3rem;
}

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

/* === FOOTER === */
footer {
  text-align: center;
  padding: 3rem 2rem;
  color: var(--text-muted);
  font-size: 0.85rem;
  border-top: 1px solid var(--border);
}

/* === ANIMATIONS === */
.fade-in {
  opacity: 0;
  transform: translateY(30px);
  transition: all 0.7s ease;
}

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

/* === RESPONSIVE === */
@media (max-width: 640px) {
  .section { padding: 3rem 1.2rem; }
  .card-grid { grid-template-columns: 1fr; }
  .sticky-nav { gap: 0.3rem; padding: 0.5rem 1rem; }
  .sticky-nav a { font-size: 0.75rem; padding: 0.4rem 0.7rem; }
  .network-visual { gap: 0.5rem; }
  .device { width: 60px; height: 60px; font-size: 1.4rem; }
  .connection { width: 30px; }
}