/* ===== Root & Global Styles ===== */
:root {
  --primary-bg: #ffffff;
  --primary-text: #1a1a1a;
  --secondary-text: #666666;
  --border-color: #e0e0e0;
  --accent-color: #0066cc;
  --accent-hover: #0052a3;
  --badge-bg: #f0f0f0;
  --code-bg: #f5f5f5;
  --category-1: #ff6b6b;
  --category-2: #4ecdc4;
  --category-3: #45b7d1;
  --category-4: #96ceb4;
  --category-5: #ffeaa7;
  --category-6: #dda0dd;
}

html.dark-mode {
  --primary-bg: #1a1a1a;
  --primary-text: #f0f0f0;
  --secondary-text: #b0b0b0;
  --border-color: #333333;
  --badge-bg: #2a2a2a;
  --code-bg: #2a2a2a;
}

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

html, body {
  height: 100%;
}

body {
  font-family: 'Noto Sans JP', 'Segoe UI', sans-serif;
  line-height: 1.8;
  color: var(--primary-text);
  background-color: var(--primary-bg);
  transition: background-color 0.3s ease, color 0.3s ease;
}

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

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

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

::-webkit-scrollbar-thumb:hover {
  background: var(--accent-color);
}

/* ===== Typography ===== */
h1, h2, h3, h4, h5, h6 {
  font-weight: 600;
  line-height: 1.4;
  margin-top: 1.5em;
  margin-bottom: 0.5em;
}

h1 {
  font-size: 2.5em;
}

h2 {
  font-size: 2em;
  border-bottom: 2px solid var(--border-color);
  padding-bottom: 0.5em;
}

h3 {
  font-size: 1.5em;
}

h4 {
  font-size: 1.25em;
}

p {
  margin-bottom: 1em;
}

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

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

strong {
  font-weight: 600;
}

em {
  font-style: italic;
}

code {
  font-family: 'Courier New', monospace;
  background-color: var(--code-bg);
  padding: 0.2em 0.4em;
  border-radius: 3px;
  font-size: 0.95em;
}

pre {
  background-color: var(--code-bg);
  padding: 1em;
  border-radius: 8px;
  overflow-x: auto;
  margin: 1.5em 0;
  border-left: 4px solid var(--accent-color);
}

pre code {
  background-color: transparent;
  padding: 0;
  border-radius: 0;
}

blockquote {
  border-left: 4px solid var(--accent-color);
  padding-left: 1em;
  margin-left: 0;
  margin-right: 0;
  margin: 1.5em 0;
  padding: 0 0 0 1em;
  color: var(--secondary-text);
  font-style: italic;
}

/* ===== Header ===== */
header {
  background-color: var(--primary-bg);
  border-bottom: 1px solid var(--border-color);
  padding: 1.5rem 0;
  position: sticky;
  top: 0;
  z-index: 100;
  transition: background-color 0.3s ease, border-color 0.3s ease;
}

nav {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 2rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.logo {
  font-size: 1.8em;
  font-weight: 700;
  color: var(--primary-text);
  display: flex;
  flex-direction: column;
  line-height: 1.1;
}

.logo-main {
  font-size: 1.2em;
}

.logo-tagline {
  font-size: 0.5em;
  color: var(--secondary-text);
  font-weight: 400;
}

.nav-controls {
  display: flex;
  align-items: center;
  gap: 2rem;
}

.search-box {
  position: relative;
}

.search-box input {
  padding: 0.5rem 1rem;
  border: 1px solid var(--border-color);
  border-radius: 24px;
  background-color: var(--badge-bg);
  color: var(--primary-text);
  width: 200px;
  transition: all 0.2s ease;
  font-size: 0.9em;
}

.search-box input:focus {
  outline: none;
  border-color: var(--accent-color);
  background-color: var(--primary-bg);
}

.search-box input::placeholder {
  color: var(--secondary-text);
}

.dark-toggle {
  background: none;
  border: none;
  cursor: pointer;
  font-size: 1.2em;
  padding: 0.5rem;
  color: var(--primary-text);
  transition: transform 0.2s ease;
}

.dark-toggle:hover {
  transform: scale(1.1);
}

/* ===== Main Container ===== */
main {
  max-width: 1200px;
  margin: 0 auto;
  padding: 3rem 2rem;
  min-height: calc(100vh - 200px);
}

/* ===== Article Grid (Homepage) ===== */
.articles-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 2rem;
  margin-bottom: 3rem;
}

.article-card {
  background-color: var(--primary-bg);
  border: 1px solid var(--border-color);
  border-radius: 8px;
  padding: 2rem;
  transition: all 0.3s ease;
  cursor: pointer;
  display: flex;
  flex-direction: column;
}

.article-card:hover {
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.12);
  transform: translateY(-4px);
  border-color: var(--accent-color);
}

.article-card a {
  flex: 1;
  display: flex;
  flex-direction: column;
}

.article-meta {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1rem;
  font-size: 0.85em;
}

.category-badge {
  display: inline-block;
  padding: 0.35rem 0.8rem;
  border-radius: 20px;
  font-size: 0.75em;
  font-weight: 600;
  color: white;
  background: linear-gradient(135deg, var(--accent-color), var(--accent-hover));
}

.difficulty-stars {
  display: flex;
  gap: 0.25rem;
}

.star {
  font-size: 0.8em;
  color: var(--secondary-text);
}

.star.filled {
  color: #ffc107;
}

.article-title {
  font-size: 1.4em;
  margin-bottom: 0.8rem;
  color: var(--primary-text);
  line-height: 1.3;
  flex-grow: 1;
}

.article-excerpt {
  color: var(--secondary-text);
  font-size: 0.95em;
  line-height: 1.6;
  margin-bottom: 1.5rem;
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.article-readtime {
  color: var(--secondary-text);
  font-size: 0.85em;
}

/* ===== Category Filter ===== */
.category-filter {
  display: flex;
  gap: 1rem;
  margin-bottom: 2rem;
  overflow-x: auto;
  padding-bottom: 1rem;
}

.category-filter button {
  padding: 0.5rem 1.2rem;
  border: 2px solid var(--border-color);
  background-color: transparent;
  border-radius: 24px;
  cursor: pointer;
  white-space: nowrap;
  font-family: 'Noto Sans JP', sans-serif;
  font-size: 0.9em;
  color: var(--primary-text);
  transition: all 0.2s ease;
}

.category-filter button:hover,
.category-filter button.active {
  border-color: var(--accent-color);
  color: var(--accent-color);
  background-color: var(--badge-bg);
}

/* ===== Article Page ===== */
.article-container {
  max-width: 720px;
  margin: 0 auto;
}

.article-header {
  margin-bottom: 3rem;
}

.article-title-main {
  font-size: 2.5em;
  margin-bottom: 1.5rem;
  line-height: 1.2;
}

.article-info {
  display: flex;
  flex-wrap: wrap;
  gap: 2rem;
  align-items: center;
  font-size: 0.9em;
  color: var(--secondary-text);
  padding-bottom: 2rem;
  border-bottom: 1px solid var(--border-color);
}

.article-info-item {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.article-toc {
  background-color: var(--badge-bg);
  border-radius: 8px;
  padding: 1.5rem;
  margin: 2rem 0;
  position: sticky;
  top: 80px;
  max-height: 500px;
  overflow-y: auto;
}

.article-toc h4 {
  margin-top: 0;
  margin-bottom: 1rem;
  font-size: 1em;
}

.article-toc ul {
  list-style: none;
}

.article-toc li {
  margin-bottom: 0.5rem;
}

.article-toc a {
  font-size: 0.9em;
  color: var(--accent-color);
}

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

.article-toc .toc-level-2 {
  margin-left: 1rem;
}

.article-toc .toc-level-3 {
  margin-left: 2rem;
}

.article-content {
  line-height: 1.9;
  color: var(--primary-text);
}

.article-content h2 {
  margin-top: 2em;
  margin-bottom: 1rem;
  font-size: 1.8em;
}

.article-content h3 {
  margin-top: 1.5em;
  margin-bottom: 0.8rem;
  font-size: 1.3em;
}

.article-content img {
  max-width: 100%;
  height: auto;
  border-radius: 8px;
  margin: 2rem 0;
}

.article-content table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.5rem 0;
}

.article-content table th,
.article-content table td {
  border: 1px solid var(--border-color);
  padding: 0.8rem;
  text-align: left;
}

.article-content table th {
  background-color: var(--badge-bg);
  font-weight: 600;
}

/* ===== Share Buttons ===== */
.article-share {
  display: flex;
  gap: 1rem;
  margin: 3rem 0;
  padding: 2rem 0;
  border-top: 1px solid var(--border-color);
  border-bottom: 1px solid var(--border-color);
}

.share-button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background-color: var(--badge-bg);
  color: var(--primary-text);
  border: 1px solid var(--border-color);
  cursor: pointer;
  transition: all 0.2s ease;
  text-decoration: none;
  font-size: 1.2em;
}

.share-button:hover {
  background-color: var(--accent-color);
  color: white;
  border-color: var(--accent-color);
}

/* ===== Navigation Links ===== */
.article-nav {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 2rem;
  margin: 3rem 0;
}

.nav-link {
  padding: 1.5rem;
  border: 1px solid var(--border-color);
  border-radius: 8px;
  transition: all 0.2s ease;
  text-decoration: none;
  color: var(--primary-text);
}

.nav-link:hover {
  border-color: var(--accent-color);
  background-color: var(--badge-bg);
}

.nav-link-label {
  font-size: 0.85em;
  color: var(--secondary-text);
  display: block;
  margin-bottom: 0.5rem;
}

.nav-link-title {
  font-size: 1.1em;
  font-weight: 600;
}

.nav-link.prev {
  text-align: left;
}

.nav-link.next {
  text-align: right;
}

/* ===== Footer ===== */
footer {
  background-color: var(--primary-bg);
  border-top: 1px solid var(--border-color);
  padding: 3rem 2rem;
  margin-top: 4rem;
  color: var(--secondary-text);
  text-align: center;
}

footer p {
  margin-bottom: 0.5rem;
}

/* ===== Responsive Design ===== */
@media (max-width: 768px) {
  nav {
    padding: 0 1rem;
    flex-direction: column;
    gap: 1rem;
  }

  .nav-controls {
    width: 100%;
    justify-content: center;
    gap: 1rem;
  }

  .search-box input {
    width: 100%;
  }

  main {
    padding: 1.5rem 1rem;
  }

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

  .article-title-main {
    font-size: 1.8em;
  }

  .article-toc {
    position: static;
    max-height: none;
  }

  .category-filter {
    flex-wrap: nowrap;
  }

  .article-nav {
    grid-template-columns: 1fr;
  }

  h1 {
    font-size: 1.8em;
  }

  h2 {
    font-size: 1.5em;
  }
}

@media (max-width: 480px) {
  .logo {
    font-size: 1.3em;
  }

  .article-meta {
    flex-direction: column;
    align-items: flex-start;
    gap: 0.5rem;
  }

  .article-title {
    font-size: 1.2em;
  }

  .article-title-main {
    font-size: 1.5em;
  }

  .article-info {
    flex-direction: column;
    gap: 1rem;
  }

  h1 {
    font-size: 1.5em;
  }

  .article-share {
    flex-direction: column;
  }

  .share-button {
    width: 100%;
    justify-content: flex-start;
  }
}

/* ===== Print Styles ===== */
@media print {
  header, footer, .article-share, .article-nav, .article-toc {
    display: none;
  }

  body {
    background-color: white;
    color: black;
  }

  a {
    color: inherit;
  }
}