/* ===== CSS Variables ===== */
:root {
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --bg: #0f172a;
  --bg-card: #1e293b;
  --bg-card-hover: #334155;
  --text: #f1f5f9;
  --text-muted: #94a3b8;
  --border: #334155;
  --accent: #22d3ee;
  --code-bg: #0d1117;
  --success: #10b981;
  --warning: #f59e0b;
}

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

html {
  scroll-behavior: smooth;
}

body {
  font-family: 'Pretendard', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

a {
  color: var(--primary);
  text-decoration: none;
  transition: color 0.2s;
}

a:hover {
  color: var(--accent);
}

img {
  max-width: 100%;
  height: auto;
}

/* ===== Reading Progress Bar ===== */
.reading-progress {
  position: fixed;
  top: 0;
  left: 0;
  width: 0%;
  height: 3px;
  background: linear-gradient(90deg, var(--accent), var(--primary));
  z-index: 9999;
  transition: width 0.1s linear;
  border-radius: 0 2px 2px 0;
  box-shadow: 0 0 8px rgba(34, 211, 238, 0.4);
}

/* ===== Reading Time Badge ===== */
.reading-time-badge {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  color: var(--accent);
  padding: 4px 12px;
  border-radius: 20px;
  font-size: 0.8rem;
  font-weight: 500;
  margin-left: 8px;
  white-space: nowrap;
}

.reading-time-badge::before {
  content: '\23F1';
  font-size: 0.85em;
}

/* ===== Table of Contents (TOC) Sidebar ===== */
.toc-sidebar {
  position: fixed;
  top: 100px;
  left: max(10px, calc((100vw - 1100px) / 2 - 260px));
  width: 230px;
  max-height: calc(100vh - 140px);
  overflow-y: auto;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 20px;
  z-index: 50;
  transition: opacity 0.3s, transform 0.3s;
  scrollbar-width: thin;
  scrollbar-color: var(--border) transparent;
}

.toc-sidebar::-webkit-scrollbar {
  width: 4px;
}

.toc-sidebar::-webkit-scrollbar-thumb {
  background: var(--border);
  border-radius: 2px;
}

.toc-sidebar .toc-title {
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: 14px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border);
}

.toc-sidebar ul {
  list-style: none;
  padding: 0;
  margin: 0;
}

.toc-sidebar li {
  margin-bottom: 2px;
}

.toc-sidebar a {
  display: block;
  padding: 5px 10px;
  font-size: 0.82rem;
  color: var(--text-muted);
  border-radius: 6px;
  border-left: 2px solid transparent;
  transition: all 0.2s;
  line-height: 1.5;
}

.toc-sidebar a:hover {
  color: var(--text);
  background: rgba(34, 211, 238, 0.05);
}

.toc-sidebar a.active {
  color: var(--accent);
  border-left-color: var(--accent);
  background: rgba(34, 211, 238, 0.08);
}

.toc-sidebar li.toc-h3 a {
  padding-left: 22px;
  font-size: 0.78rem;
}

/* ===== Back to Top Button ===== */
.back-to-top {
  position: fixed;
  bottom: 30px;
  right: 30px;
  width: 46px;
  height: 46px;
  border-radius: 50%;
  background: var(--primary);
  color: white;
  border: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.2rem;
  z-index: 90;
  opacity: 0;
  visibility: hidden;
  transform: translateY(20px);
  transition: opacity 0.3s, visibility 0.3s, transform 0.3s, background 0.2s;
  box-shadow: 0 4px 15px rgba(37, 99, 235, 0.4);
}

.back-to-top.visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.back-to-top:hover {
  background: var(--accent);
  box-shadow: 0 4px 20px rgba(34, 211, 238, 0.4);
}

.back-to-top::after {
  content: '';
  display: block;
  width: 10px;
  height: 10px;
  border-top: 2.5px solid white;
  border-right: 2.5px solid white;
  transform: rotate(-45deg) translateY(2px);
}

/* ===== Code Block with Copy Button ===== */
.code-block-wrapper {
  position: relative;
}

.code-copy-btn {
  position: absolute;
  top: 8px;
  right: 8px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  color: var(--text-muted);
  padding: 4px 10px;
  border-radius: 6px;
  font-size: 0.72rem;
  cursor: pointer;
  opacity: 0;
  transition: opacity 0.2s, background 0.2s, color 0.2s;
  z-index: 5;
  font-family: inherit;
}

.code-block-wrapper:hover .code-copy-btn {
  opacity: 1;
}

.code-copy-btn:hover {
  background: var(--primary);
  color: white;
  border-color: var(--primary);
}

.code-copy-btn.copied {
  background: var(--success);
  color: white;
  border-color: var(--success);
  opacity: 1;
}

/* ===== Share Buttons ===== */
.share-section {
  margin-top: 50px;
  padding-top: 30px;
  border-top: 1px solid var(--border);
}

.share-section .share-title {
  font-size: 1rem;
  font-weight: 600;
  color: var(--text-muted);
  margin-bottom: 14px;
}

.share-buttons {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

.share-btn {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  padding: 9px 18px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--bg-card);
  color: var(--text-muted);
  font-size: 0.85rem;
  font-family: inherit;
  cursor: pointer;
  transition: all 0.2s;
}

.share-btn:hover {
  border-color: var(--accent);
  color: var(--text);
  background: rgba(34, 211, 238, 0.08);
}

.share-btn.twitter:hover {
  border-color: #1da1f2;
  color: #1da1f2;
}

.share-btn.linkedin:hover {
  border-color: #0a66c2;
  color: #0a66c2;
}

.share-btn.copy-link.copied {
  border-color: var(--success);
  color: var(--success);
}

.share-btn svg {
  width: 16px;
  height: 16px;
  fill: currentColor;
}

/* ===== Related Posts Section ===== */
.related-posts {
  margin-top: 50px;
  padding-top: 30px;
  border-top: 1px solid var(--border);
}

.related-posts .related-title {
  font-size: 1.3rem;
  font-weight: 700;
  margin-bottom: 20px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.related-posts .related-title::before {
  content: '';
  width: 3px;
  height: 22px;
  background: var(--accent);
  border-radius: 2px;
}

.related-posts-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 16px;
}

.related-post-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 18px;
  transition: transform 0.2s, border-color 0.2s;
}

.related-post-card:hover {
  transform: translateY(-2px);
  border-color: var(--accent);
}

.related-post-card a {
  color: var(--text);
  font-weight: 600;
  font-size: 0.95rem;
  line-height: 1.4;
  display: block;
  margin-bottom: 8px;
}

.related-post-card a:hover {
  color: var(--accent);
}

.related-post-card .related-post-meta {
  color: var(--text-muted);
  font-size: 0.78rem;
}

/* ===== Layout ===== */
.container {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 20px;
}

main {
  flex: 1;
}

/* ===== Header ===== */
header {
  background: rgba(30, 41, 59, 0.95);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 100;
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
}

header .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  height: 70px;
}

.logo {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--text);
  display: flex;
  align-items: center;
  gap: 8px;
}

.logo span {
  color: var(--accent);
}

nav {
  display: flex;
  gap: 30px;
}

nav a {
  color: var(--text-muted);
  font-weight: 500;
  padding: 8px 0;
  position: relative;
  transition: color 0.2s;
}

nav a:hover,
nav a.active {
  color: var(--text);
}

nav a.active::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: var(--accent);
  border-radius: 1px;
}

/* Mobile Menu */
.menu-toggle {
  display: none;
  background: none;
  border: none;
  color: var(--text);
  font-size: 1.5rem;
  cursor: pointer;
  padding: 4px;
}

/* ===== Hero Section ===== */
.hero {
  padding: 80px 0;
  text-align: center;
  background: linear-gradient(135deg, var(--bg) 0%, var(--bg-card) 100%);
}

.hero h1 {
  font-size: 2.8rem;
  margin-bottom: 20px;
  background: linear-gradient(135deg, var(--text) 0%, var(--accent) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero p {
  font-size: 1.2rem;
  color: var(--text-muted);
  max-width: 600px;
  margin: 0 auto;
  line-height: 1.8;
}

/* ===== Posts Grid ===== */
.section-title {
  font-size: 1.8rem;
  margin-bottom: 30px;
  display: flex;
  align-items: center;
  gap: 10px;
}

.section-title::before {
  content: '';
  width: 4px;
  height: 28px;
  background: var(--accent);
  border-radius: 2px;
}

.posts-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 24px;
  padding: 40px 0;
}

.post-card {
  background: var(--bg-card);
  border-radius: 12px;
  overflow: hidden;
  border: 1px solid var(--border);
  transition: transform 0.3s, border-color 0.3s, box-shadow 0.3s;
}

.post-card:hover {
  transform: translateY(-4px);
  border-color: var(--accent);
  box-shadow: 0 10px 40px rgba(34, 211, 238, 0.1);
}

.post-card-content {
  padding: 24px;
  display: flex;
  flex-direction: column;
  height: 100%;
}

.post-tag {
  display: inline-block;
  background: var(--primary);
  color: white;
  padding: 4px 12px;
  border-radius: 20px;
  font-size: 0.75rem;
  font-weight: 600;
  margin-bottom: 12px;
  width: fit-content;
}

.post-card h3 {
  font-size: 1.2rem;
  margin-bottom: 12px;
  line-height: 1.4;
}

.post-card h3 a {
  color: var(--text);
  transition: color 0.2s;
}

.post-card h3 a:hover {
  color: var(--accent);
}

.post-card p {
  color: var(--text-muted);
  font-size: 0.93rem;
  margin-bottom: 16px;
  flex: 1;
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.post-meta {
  display: flex;
  justify-content: space-between;
  align-items: center;
  color: var(--text-muted);
  font-size: 0.85rem;
}

/* ===== Single Post ===== */
.post-header {
  padding: 60px 0 40px;
  text-align: center;
  border-bottom: 1px solid var(--border);
}

.post-header h1 {
  font-size: 2.4rem;
  margin-bottom: 20px;
  line-height: 1.3;
  max-width: 800px;
  margin-left: auto;
  margin-right: auto;
}

.post-header .post-meta {
  justify-content: center;
  gap: 20px;
}

.post-content {
  max-width: 800px;
  margin: 0 auto;
  padding: 50px 20px;
}

.post-content h2 {
  font-size: 1.6rem;
  margin: 40px 0 20px;
  color: var(--accent);
  padding-bottom: 8px;
  border-bottom: 1px solid var(--border);
}

.post-content h3 {
  font-size: 1.3rem;
  margin: 30px 0 15px;
}

.post-content p {
  margin-bottom: 20px;
}

.post-content ul,
.post-content ol {
  margin: 20px 0;
  padding-left: 30px;
}

.post-content li {
  margin-bottom: 10px;
}

.post-content pre {
  background: var(--code-bg);
  padding: 20px;
  border-radius: 8px;
  overflow-x: auto;
  margin: 25px 0;
  border: 1px solid var(--border);
  line-height: 1.5;
}

.post-content code {
  font-family: 'Fira Code', 'Consolas', monospace;
  font-size: 0.88rem;
}

.post-content p code {
  background: var(--code-bg);
  padding: 2px 8px;
  border-radius: 4px;
  color: var(--accent);
  font-size: 0.9em;
}

.post-content blockquote {
  border-left: 4px solid var(--accent);
  padding-left: 20px;
  margin: 25px 0;
  color: var(--text-muted);
  font-style: italic;
}

.post-content strong {
  color: var(--text);
}

/* Post navigation */
.post-nav {
  display: flex;
  justify-content: space-between;
  padding: 40px 0;
  border-top: 1px solid var(--border);
  margin-top: 40px;
}

.post-nav a {
  color: var(--text-muted);
  transition: color 0.2s;
}

.post-nav a:hover {
  color: var(--accent);
}

/* ===== Page Content ===== */
.page-header {
  padding: 60px 0 40px;
  text-align: center;
}

.page-header h1 {
  font-size: 2.4rem;
}

.page-content {
  max-width: 800px;
  margin: 0 auto;
  padding: 40px 20px 80px;
}

.page-content h2 {
  font-size: 1.5rem;
  margin: 40px 0 20px;
  color: var(--accent);
}

.page-content p {
  margin-bottom: 20px;
  color: var(--text-muted);
}

.page-content ul {
  margin: 20px 0;
  padding-left: 25px;
}

.page-content li {
  margin-bottom: 10px;
  color: var(--text-muted);
}

/* ===== Contact Form ===== */
.contact-info {
  background: var(--bg-card);
  padding: 30px;
  border-radius: 12px;
  margin-bottom: 40px;
}

.contact-info p {
  margin-bottom: 10px;
}

/* ===== Footer ===== */
footer {
  background: var(--bg-card);
  border-top: 1px solid var(--border);
  padding: 40px 0;
  margin-top: 60px;
}

.footer-content {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 20px;
}

.footer-links {
  display: flex;
  gap: 25px;
  flex-wrap: wrap;
}

.footer-links a {
  color: var(--text-muted);
  font-size: 0.9rem;
}

.footer-links a:hover {
  color: var(--text);
}

.copyright {
  color: var(--text-muted);
  font-size: 0.9rem;
}

/* ===== Responsive ===== */
@media (max-width: 1400px) {
  .toc-sidebar {
    display: none;
  }
}

@media (max-width: 768px) {
  .hero {
    padding: 50px 0;
  }

  .hero h1 {
    font-size: 2rem;
  }

  .hero p {
    font-size: 1rem;
  }

  nav {
    display: none;
    position: absolute;
    top: 70px;
    left: 0;
    right: 0;
    background: var(--bg-card);
    flex-direction: column;
    padding: 20px;
    gap: 15px;
    border-bottom: 1px solid var(--border);
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.3);
  }

  nav.active {
    display: flex;
  }

  .menu-toggle {
    display: block;
  }

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

  .post-header h1 {
    font-size: 1.8rem;
    padding: 0 10px;
  }

  .post-content {
    padding: 30px 16px;
  }

  .post-content pre {
    padding: 14px;
    font-size: 0.82rem;
  }

  .section-title {
    font-size: 1.5rem;
  }

  .footer-content {
    flex-direction: column;
    text-align: center;
  }

  .footer-links {
    justify-content: center;
  }

  .share-buttons {
    justify-content: center;
  }

  .related-posts-grid {
    grid-template-columns: 1fr;
  }

  .back-to-top {
    bottom: 20px;
    right: 20px;
    width: 40px;
    height: 40px;
  }
}

@media (max-width: 480px) {
  .hero h1 {
    font-size: 1.6rem;
  }

  .post-header h1 {
    font-size: 1.5rem;
  }

  .post-content h2 {
    font-size: 1.35rem;
  }

  .post-content h3 {
    font-size: 1.15rem;
  }
}

/* ===== Ads Container ===== */
.ad-container {
  margin: 30px 0;
  text-align: center;
  min-height: 100px;
  background: var(--bg-card);
  border-radius: 8px;
  display: flex;
  align-items: center;
  justify-content: center;
}

/* ===== Utilities ===== */
.text-center {
  text-align: center;
}

.mt-4 {
  margin-top: 40px;
}

.mb-4 {
  margin-bottom: 40px;
}

/* ===== Accessibility ===== */
:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

/* Skip link for screen readers */
.skip-link {
  position: absolute;
  top: -40px;
  left: 0;
  background: var(--accent);
  color: var(--bg);
  padding: 8px;
  z-index: 200;
}

.skip-link:focus {
  top: 0;
}

/* ===== Selection ===== */
::selection {
  background: var(--primary);
  color: white;
}

/* ===== Scrollbar ===== */
::-webkit-scrollbar {
  width: 8px;
}

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

::-webkit-scrollbar-thumb {
  background: var(--border);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--text-muted);
}