/* ============================================
   Design System / CSS Variables
   ============================================ */
:root {
  --bg-primary: #0b0d12;
  --bg-secondary: #12141c;
  --bg-tertiary: #1a1d28;
  --bg-card: #161922;
  --border: #2a2d3a;
  --border-hover: #3a3d4a;
  --text-primary: #e4e5e9;
  --text-secondary: #8b8e9e;
  --text-muted: #5a5d6e;
  --accent: #4c8cff;
  --accent-hover: #3a7bf5;
  --accent-subtle: rgba(76, 140, 255, 0.08);
  --accent-secondary: #00d4aa;
  --accent-secondary-subtle: rgba(0, 212, 170, 0.08);
  --gradient: linear-gradient(135deg, #4c8cff, #00d4aa);
  --radius-sm: 6px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.5);
  --nav-height: 64px;
  --max-width: 1120px;
  --font-sans: 'Inter', system-ui, -apple-system, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
 --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
}
/* ============================================
   Reset & Base
   ============================================ */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
html {
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}
body {
  font-family: var(--font-sans);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  font-size: 16px;
  min-height: 100vh;
}
a {
  color: var(--text-primary);
  text-decoration: none;
  transition: color 0.2s ease;
}
a:hover {
  color: var(--accent);
}
img {
  max-width: 100%;
  height: auto;
  display: block;
}
::selection {
  background: var(--accent-subtle);
  color: var(--text-primary);
}
  background: var(--accent-subtle);
  color: var(--text-primary);
}
/* ============================================
   Typography
   ============================================ */
h1, h2, h3, h4, h5, h6 {
  line-height: 1.25;
  font-weight: 600;
  letter-spacing: -0.02em;
}
p {
  margin-bottom: 1rem;
  color: var(--text-secondary);
}
.text-gradient {
  background: var(--gradient);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.text-muted {
  color: var(--text-muted);
}
.text-secondary {
  color: var(--text-secondary);
}
.text-sm {
  font-size: 0.875rem;
}
.text-xs {
  font-size: 0.75rem;
}
/* ============================================
   Container & Layout
   ============================================ */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
}
.container-narrow {
  max-width: 720px;
  margin: 0 auto;
  padding: 0 24px;
}
.section {
  padding: 80px 0;
}
.section-header {
  text-align: center;
  margin-bottom: 48px;
}
.section-header h2 {
  font-size: 2rem;
  margin-bottom: 12px;
}
.section-header p {
  font-size: 1.125rem;
  max-width: 540px;
  margin: 0 auto;
}
.grid-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
}
.grid-2 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 24px;
}
  gap: 24px;
}
/* ============================================
   Button Component
   ============================================ */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 20px;
  border: none;
  border-radius: var(--radius-md);
  font-family: var(--font-sans);
  font-size: 0.925rem;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s var(--ease-out);
  text-decoration: none;
  line-height: 1.4;
}
.btn-primary {
  background: var(--accent);
  color: #fff;
}
.btn-primary:hover {
  background: var(--accent-hover);
  color: #fff;
  transform: translateY(-1px);
  box-shadow: 0 4px 16px rgba(76, 140, 255, 0.25);
}
.btn-ghost {
  background: transparent;
  color: var(--text-primary);
  border: 1px solid var(--border);
}
.btn-ghost:hover {
  background: var(--bg-tertiary);
  border-color: var(--border-hover);
  color: var(--text-primary);
  transform: translateY(-1px);
}
.btn-lg {
  padding: 14px 28px;
  font-size: 1rem;
}
/* ============================================
   Navigation
   ============================================ */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: rgba(11, 13, 18, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
  z-index: 100;
}
.nav-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.nav-logo {
  font-size: 1.25rem;
  font-weight: 700;
  letter-spacing: -0.03em;
}
.nav-logo:hover {
  color: var(--text-primary);
}
.nav-logo span {
  color: var(--accent);
}
.nav-links {
  display: flex;
  align-items: center;
  gap: 32px;
  list-style: none;
}
.nav-links a {
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--text-secondary);
  position: relative;
  transition: color 0.2s ease;
}
.nav-links a::after {
  content: '';
  position: absolute;
  bottom: -4px;
  left: 0;
  width: 0;
  height: 2px;
  background: var(--accent);
  border-radius: 1px;
  transition: width 0.2s var(--ease-out);
}
.nav-links a:hover {
  color: var(--text-primary);
}
.nav-links a:hover::after {
  width: 100%;
}
.nav-links a.active {
  color: var(--text-primary);
}
.nav-links a.active::after {
  width: 100%;
}
.nav-cta {
  margin-left: 8px;
}
.nav-toggle {
  display: none;
  background: none;
  border: none;
  color: var(--text-primary);
  cursor: pointer;
  padding: 8px;
}
.nav-toggle svg {
  width: 24px;
  height: 24px;
}
/* ============================================
   Hero Section
   ============================================ */
.hero {
  min-height: 100vh;
  display: flex;
  align-items: center;
  position: relative;
  overflow: hidden;
  padding: calc(var(--nav-height) + 40px) 0 80px;
}
.hero-grid-bg {
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(var(--border) 1px, transparent 1px),
    linear-gradient(90deg, var(--border) 1px, transparent 1px);
  background-size: 64px 64px;
  opacity: 0.3;
  mask-image: radial-gradient(ellipse at center, black 30%, transparent 70%);
  -webkit-mask-image: radial-gradient(ellipse at center, black 30%, transparent 70%);
  pointer-events: none;
}
.hero-glow {
  position: absolute;
  top: -20%;
  left: 50%;
  transform: translateX(-50%);
  width: 600px;
  height: 600px;
  background: radial-gradient(circle, rgba(76, 140, 255, 0.08) 0%, transparent 70%);
  pointer-events: none;
}
.hero-content {
  position: relative;
  z-index: 1;
  max-width: 800px;
  margin: 0 auto;
  text-align: center;
}
.hero-label {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 6px 14px;
  border: 1px solid var(--border);
  border-radius: 100px;
  font-size: 0.8rem;
  color: var(--text-secondary);
  margin-bottom: 24px;
  letter-spacing: 0.05em;
}
.hero-label-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--accent);
  animation: pulse-dot 2s infinite;
}
@keyframes pulse-dot {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.4; }
}
.hero h1 {
  font-size: 3.5rem;
  font-weight: 700;
  line-height: 1.15;
  margin-bottom: 20px;
  letter-spacing: -0.03em;
}
.hero h1 .highlight {
  color: transparent;
  background: var(--gradient);
  -webkit-background-clip: text;
  background-clip: text;
}
.hero p {
  font-size: 1.2rem;
  color: var(--text-secondary);
  max-width: 600px;
  margin: 0 auto 32px;
  line-height: 1.7;
}
.hero-actions {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 16px;
  flex-wrap: wrap;
}
/* ============================================
   Featured Posts / Post Cards
   ============================================ */
.featured {
  background: var(--bg-secondary);
}
.post-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 28px;
  transition: all 0.3s var(--ease-out);
  display: flex;
  flex-direction: column;
}
.post-card:hover {
  border-color: var(--border-hover);
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}
.post-card-category {
  display: inline-block;
  padding: 4px 10px;
  border-radius: var(--radius-sm);
  font-size: 0.75rem;
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-bottom: 16px;
  width: fit-content;
}
.post-card-category.blue {
  background: var(--accent-subtle);
  color: var(--accent);
}
.post-card-category.teal {
  background: var(--accent-secondary-subtle);
  color: var(--accent-secondary);
}
.post-card h3 {
  font-size: 1.125rem;
  margin-bottom: 10px;
  line-height: 1.35;
}
.post-card h3 a {
  color: var(--text-primary);
}
.post-card h3 a:hover {
  color: var(--accent);
}
.post-card p {
  font-size: 0.9rem;
  color: var(--text-muted);
  margin-bottom: 16px;
  flex: 1;
}
.post-card-meta {
  display: flex;
  align-items: center;
  gap: 12px;
  font-size: 0.8rem;
  color: var(--text-muted);
  padding-top: 16px;
  border-top: 1px solid var(--border);
}
.post-card-meta .dot {
  width: 3px;
  height: 3px;
  border-radius: 50%;
  background: var(--text-muted);
}
/* ============================================
   Philosophy Section
   ============================================ */
.philosophy-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 32px;
  transition: border-color 0.2s ease;
}
.philosophy-card:hover {
  border-color: var(--border-hover);
}
.philosophy-icon {
  width: 44px;
  height: 44px;
  border-radius: var(--radius-md);
  background: var(--accent-subtle);
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 20px;
}
.philosophy-icon svg {
  width: 22px;
  height: 22px;
  color: var(--accent);
}
.philosophy-card h3 {
  font-size: 1.1rem;
  margin-bottom: 10px;
}
.philosophy-card p {
  font-size: 0.9rem;
  color: var(--text-muted);
  margin-bottom: 0;
}
/* ============================================
   CTA / Newsletter
   ============================================ */
.cta-section {
  background: var(--bg-secondary);
  text-align: center;
}
.cta-section h2 {
  font-size: 2rem;
  margin-bottom: 12px;
}
.cta-section p {
  max-width: 480px;
  margin: 0 auto 28px;
}
.cta-form {
  display: flex;
  gap: 12px;
  max-width: 440px;
  margin: 0 auto;
}
.cta-form input {
  flex: 1;
  padding: 12px 16px;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  background: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-sans);
  font-size: 0.925rem;
  outline: none;
  transition: border-color 0.2s ease;
}
.cta-form input:focus {
  border-color: var(--accent);
}
.cta-form input::placeholder {
  color: var(--text-muted);
}
/* ============================================
   Footer
   ============================================ */
.footer {
  padding: 48px 0 24px;
  border-top: 1px solid var(--border);
}
.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr;
  gap: 48px;
  margin-bottom: 40px;
}
.footer-brand p {
  font-size: 0.9rem;
  margin-top: 12px;
  max-width: 320px;
}
.footer h4 {
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-muted);
  margin-bottom: 16px;
}
.footer-links {
  list-style: none;
}
.footer-links li {
  margin-bottom: 10px;
}
.footer-links a {
  font-size: 0.9rem;
  color: var(--text-secondary);
}
.footer-links a:hover {
  color: var(--accent);
}
.footer-bottom {
  padding-top: 24px;
  border-top: 1px solid var(--border);
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.8rem;
  color: var(--text-muted);
}
  color: var(--text-muted);
}
/* ============================================
   Blog Listing Page
   ============================================ */
.page-header {
  padding: calc(var(--nav-height) + 48px) 0 32px;
}
.page-header h1 {
  font-size: 2.5rem;
  margin-bottom: 12px;
}
.page-header p {
  font-size: 1.1rem;
  max-width: 540px;
}
.blog-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 24px;
  padding-bottom: 80px;
}
.blog-grid .post-card-wide {
  grid-column: 1 / -1;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 28px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 0;
  overflow: hidden;
  transition: all 0.3s var(--ease-out);
}
.blog-grid .post-card-wide:hover {
  border-color: var(--border-hover);
  box-shadow: var(--shadow-lg);
}
.post-card-wide-content {
  padding: 32px;
  display: flex;
  flex-direction: column;
}
.post-card-wide-content h2 {
  font-size: 1.35rem;
  margin-bottom: 10px;
}
.post-card-wide-content h2 a {
  color: var(--text-primary);
}
.post-card-wide-content h2 a:hover {
  color: var(--accent);
}
.post-card-wide-image {
  background: var(--bg-tertiary);
  min-height: 240px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-muted);
  font-size: 2.5rem;
}
/* ============================================
   Article / Blog Post
   ============================================ */
.article-header {
  padding: calc(var(--nav-height) + 48px) 0 40px;
  text-align: center;
}
.article-header .post-card-category {
  margin: 0 auto 16px;
}
.article-header h1 {
  font-size: 2.5rem;
  margin-bottom: 16px;
  max-width: 680px;
  margin-left: auto;
  margin-right: auto;
}
.article-header .meta {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
  font-size: 0.875rem;
  color: var(--text-muted);
}
.article-header .meta .dot {
  width: 3px;
  height: 3px;
  border-radius: 50%;
  background: var(--text-muted);
}
.article-body {
  padding-bottom: 80px;
}
.article-body h2 {
  font-size: 1.5rem;
  margin: 48px 0 16px;
}
.article-body h3 {
  font-size: 1.2rem;
  margin: 32px 0 12px;
}
.article-body p {
  font-size: 1.025rem;
  line-height: 1.75;
  margin-bottom: 1.25rem;
  color: var(--text-secondary);
}
.article-body strong {
  color: var(--text-primary);
}
.article-body ul, .article-body ol {
  margin: 0 0 1.25rem 1.5rem;
  color: var(--text-secondary);
  line-height: 1.75;
}
.article-body li {
  margin-bottom: 6px;
}
.article-body blockquote {
  border-left: 3px solid var(--accent);
  padding: 16px 20px;
  margin: 24px 0;
  background: var(--bg-card);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
}
.article-body blockquote p {
  margin-bottom: 0;
  color: var(--text-primary);
  font-style: italic;
}
.article-body code {
  font-family: var(--font-mono);
  background: var(--bg-tertiary);
  padding: 2px 8px;
  border-radius: 4px;
  font-size: 0.875em;
}
.article-body pre {
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 20px;
  overflow-x: auto;
  margin: 24px 0;
}
.article-body pre code {
  background: none;
  padding: 0;
  font-size: 0.85rem;
  line-height: 1.6;
}
/* ============================================
   About Page
   ============================================ */
.about-hero {
  padding: calc(var(--nav-height) + 48px) 0 48px;
}
.about-layout {
  display: grid;
  grid-template-columns: 200px 1fr;
  gap: 48px;
  padding-bottom: 80px;
}
.about-avatar {
  width: 200px;
  height: 200px;
  border-radius: 50%;
  background: var(--bg-tertiary);
  display: flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--border);
  font-size: 4rem;
  color: var(--text-muted);
}
.about-content h1 {
  font-size: 2.5rem;
  margin-bottom: 8px;
}
.about-content .subtitle {
  color: var(--text-secondary);
  font-size: 1.1rem;
  margin-bottom: 24px;
}
.about-content p {
  margin-bottom: 1rem;
  line-height: 1.75;
}
.expertise-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 24px;
}
.expertise-tag {
  padding: 6px 14px;
  border: 1px solid var(--border);
  border-radius: 100px;
  font-size: 0.8rem;
  color: var(--text-secondary);
}
.expertise-tag:hover {
  border-color: var(--accent);
  color: var(--accent);
}
/* ============================================
   Courses
   ============================================ */
.course-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 32px;
  transition: all 0.3s var(--ease-out);
}
.course-card:hover {
  border-color: var(--border-hover);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}
.course-card .level {
  display: inline-block;
  padding: 4px 10px;
  border-radius: var(--radius-sm);
  font-size: 0.75rem;
  font-weight: 500;
  margin-bottom: 16px;
}
.course-card .level.beginner {
  background: var(--accent-secondary-subtle);
  color: var(--accent-secondary);
}
.course-card .level.intermediate {
  background: var(--accent-subtle);
  color: var(--accent);
}
.course-card h3 {
  font-size: 1.2rem;
  margin-bottom: 10px;
}
.course-card p {
  font-size: 0.9rem;
  color: var(--text-muted);
  margin-bottom: 20px;
}
.course-card .meta-row {
  display: flex;
  gap: 16px;
  font-size: 0.85rem;
  color: var(--text-muted);
  padding-top: 16px;
  border-top: 1px solid var(--border);
}
.course-card .meta-row span {
  display: flex;
  align-items: center;
  gap: 6px;
}
/* ============================================
   Animations
   ============================================ */
.fade-in {
  animation: fadeIn 0.6s var(--ease-out) forwards;
}
.fade-in-up {
  animation: fadeInUp 0.6s var(--ease-out) forwards;
  opacity: 0;
}
@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}
@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}
.stagger-1 { animation-delay: 0.1s; }
.stagger-2 { animation-delay: 0.2s; }
.stagger-3 { animation-delay: 0.3s; }
.stagger-3 { animation-delay: 0.3s; }
/* ============================================
   Responsive
   ============================================ */
@media (max-width: 900px) {
  .grid-3 { grid-template-columns: repeat(2, 1fr); }
  .blog-grid { grid-template-columns: 1fr; }
  .blog-grid .post-card-wide { grid-template-columns: 1fr; }
  .post-card-wide-image { min-height: 180px; order: -1; }
  .footer-grid { grid-template-columns: 1fr 1fr; }
  .footer-grid > :first-child { grid-column: 1 / -1; }
  .about-layout { grid-template-columns: 1fr; text-align: center; }
  .about-avatar { margin: 0 auto; }
  .expertise-tags { justify-content: center; }
}
@media (max-width: 768px) {
  .nav-links {
    position: fixed;
    top: var(--nav-height);
    left: 0;
    right: 0;
    background: rgba(11, 13, 18, 0.98);
    backdrop-filter: blur(12px);
    flex-direction: column;
    padding: 20px 24px;
    gap: 16px;
    transform: translateY(-100%);
    opacity: 0;
    pointer-events: none;
    transition: all 0.3s var(--ease-out);
  }
  .nav-links.open {
    transform: translateY(0);
    opacity: 1;
    pointer-events: auto;
  }
  .nav-toggle { display: block; }
  .hero h1 { font-size: 2.5rem; }
  .hero p { font-size: 1.05rem; }
  .section-header h2 { font-size: 1.6rem; }
  .grid-3 { grid-template-columns: 1fr; }
  .grid-2 { grid-template-columns: 1fr; }
  .cta-form { flex-direction: column; }
  .page-header h1 { font-size: 1.8rem; }
  .article-header h1 { font-size: 1.8rem; }
  .footer-grid { grid-template-columns: 1fr; }
  .footer-bottom { flex-direction: column; gap: 12px; text-align: center; }
  .about-content h1 { font-size: 1.8rem; }
}
@media (max-width: 480px) {
  .hero h1 { font-size: 2rem; }
  .container { padding: 0 16px; }
  .section { padding: 48px 0; }
  .post-card { padding: 20px; }
}
/* ============================================
   Utility
   ============================================ */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  border: 0;
}
.gap-8 { gap: 8px; }
.gap-12 { gap: 12px; }
.gap-16 { gap: 16px; }
.gap-24 { gap: 24px; }
.mt-12 { margin-top: 12px; }
.mt-24 { margin-top: 24px; }
.mb-12 { margin-bottom: 12px; }
.mb-24 { margin-bottom: 24px; }
.mb-48 { margin-bottom: 48px; }
.flex { display: flex; }
.flex-center { display: flex; align-items: center; justify-content: center; }
.text-center { text-align: center; }