/* =========================================
   BASE RESET & TOKENS
   ========================================= */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { font-size: 16px; scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }

:root {
  /* Light */
  --bg:          #f7f6f2;
  --surface:     #ffffff;
  --surface-2:   #f0ede6;
  --text:        #1c1b18;
  --text-2:      #5a5852;
  --text-3:      #9a9890;
  --border:      #e4e1d8;
  --border-2:    #d0ccc2;
  --accent:      #3a6b4a;
  --accent-bg:   #eaf2ec;
  --accent-text: #2c5238;
  --tag-bg:      #eeebe3;
  --tag-text:    #5a5650;

  /* Typography */
  --serif: 'Noto Serif JP', 'Georgia', 'Times New Roman', serif;
  --sans:  'Noto Sans JP', 'Hiragino Kaku Gothic ProN', system-ui, sans-serif;
  --mono:  'Menlo', 'Consolas', 'Courier New', monospace;

  /* Spacing scale */
  --sp-1: 0.25rem;
  --sp-2: 0.5rem;
  --sp-3: 0.75rem;
  --sp-4: 1rem;
  --sp-5: 1.25rem;
  --sp-6: 1.5rem;
  --sp-8: 2rem;
  --sp-10: 2.5rem;
  --sp-12: 3rem;

  /* Layout */
  --max-w: 680px;
  --r-sm: 6px;
  --r-md: 10px;
  --r-lg: 16px;
}

/* Dark mode — respects system, overrides via [data-theme="dark"] */
@media (prefers-color-scheme: dark) { :root { --is-dark: 1; } }

:root[data-theme="light"] {
  --bg:          #f7f6f2;
  --surface:     #ffffff;
  --surface-2:   #f0ede6;
  --text:        #1c1b18;
  --text-2:      #5a5852;
  --text-3:      #9a9890;
  --border:      #e4e1d8;
  --border-2:    #d0ccc2;
  --accent:      #3a6b4a;
  --accent-bg:   #eaf2ec;
  --accent-text: #2c5238;
  --tag-bg:      #eeebe3;
  --tag-text:    #5a5650;
}

:root[data-theme="dark"],
@media (prefers-color-scheme: dark) { :root:not([data-theme="light"]) {
  --bg:          #111110;
  --surface:     #1a1a18;
  --surface-2:   #232320;
  --text:        #e8e5de;
  --text-2:      #9a9890;
  --text-3:      #5a5852;
  --border:      #2a2a26;
  --border-2:    #3a3a34;
  --accent:      #72b585;
  --accent-bg:   #1a2e20;
  --accent-text: #8dcca0;
  --tag-bg:      #252420;
  --tag-text:    #9a9488;
}}

:root[data-theme="dark"] {
  --bg:          #111110;
  --surface:     #1a1a18;
  --surface-2:   #232320;
  --text:        #e8e5de;
  --text-2:      #9a9890;
  --text-3:      #5a5852;
  --border:      #2a2a26;
  --border-2:    #3a3a34;
  --accent:      #72b585;
  --accent-bg:   #1a2e20;
  --accent-text: #8dcca0;
  --tag-bg:      #252420;
  --tag-text:    #9a9488;
}

/* =========================================
   GLOBAL
   ========================================= */
body {
  background: var(--bg);
  color: var(--text);
  font-family: var(--sans);
  font-size: 1rem;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
  transition: background 0.2s, color 0.2s;
}
img { max-width: 100%; display: block; }
a { color: inherit; }

/* =========================================
   HEADER
   ========================================= */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
}
.header-inner {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 0 var(--sp-5);
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--sp-4);
}
.site-logo {
  font-family: var(--serif);
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--text);
  text-decoration: none;
  letter-spacing: 0.03em;
  flex-shrink: 0;
}
.header-actions {
  display: flex;
  align-items: center;
  gap: var(--sp-2);
}
.nav-link {
  font-size: 0.82rem;
  color: var(--text-2);
  text-decoration: none;
  padding: var(--sp-2) var(--sp-3);
  border-radius: var(--r-sm);
  transition: color 0.15s, background 0.15s;
  white-space: nowrap;
}
.nav-link:hover { color: var(--text); background: var(--surface-2); }

/* Dark mode toggle */
.theme-btn {
  width: 40px;
  height: 40px;
  border: none;
  background: transparent;
  cursor: pointer;
  border-radius: var(--r-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-2);
  transition: color 0.15s, background 0.15s;
  flex-shrink: 0;
}
.theme-btn:hover { color: var(--text); background: var(--surface-2); }
.theme-btn svg { width: 18px; height: 18px; }
.icon-sun { display: none; }
.icon-moon { display: block; }
[data-theme="dark"] .icon-sun { display: block; }
[data-theme="dark"] .icon-moon { display: none; }
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .icon-sun { display: block; }
  :root:not([data-theme="light"]) .icon-moon { display: none; }
}

/* =========================================
   MAIN WRAPPER
   ========================================= */
.page {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: var(--sp-10) var(--sp-5) var(--sp-12);
}

/* =========================================
   TAG CHIP
   ========================================= */
.tag {
  display: inline-flex;
  align-items: center;
  font-size: 0.7rem;
  font-weight: 500;
  letter-spacing: 0.04em;
  background: var(--tag-bg);
  color: var(--tag-text);
  padding: 0.2em 0.65em;
  border-radius: var(--r-sm);
  text-decoration: none;
  transition: background 0.15s;
  white-space: nowrap;
}
.tag:hover { background: var(--border-2); }
.tag.accent {
  background: var(--accent-bg);
  color: var(--accent-text);
}

/* =========================================
   INDEX — HERO ARTICLE
   ========================================= */
.hero {
  padding-bottom: var(--sp-10);
  border-bottom: 1px solid var(--border);
  margin-bottom: var(--sp-10);
}
.hero .tag { margin-bottom: var(--sp-4); }
.hero-title {
  font-family: var(--serif);
  font-size: clamp(1.55rem, 6vw, 2rem);
  font-weight: 600;
  line-height: 1.42;
  letter-spacing: 0.01em;
  margin-bottom: var(--sp-4);
}
.hero-title a { text-decoration: none; color: var(--text); }
.hero-title a:hover { color: var(--accent); }
.hero-desc {
  font-size: 0.92rem;
  color: var(--text-2);
  line-height: 1.75;
  margin-bottom: var(--sp-5);
}
.hero-meta { display: flex; align-items: center; gap: var(--sp-3); }
.meta-item {
  font-size: 0.75rem;
  color: var(--text-3);
}
.meta-dot { color: var(--border-2); }
.read-more {
  display: inline-flex;
  align-items: center;
  gap: var(--sp-2);
  margin-top: var(--sp-6);
  font-size: 0.85rem;
  font-weight: 500;
  color: var(--accent);
  text-decoration: none;
  padding: var(--sp-3) var(--sp-5);
  border: 1px solid var(--accent);
  border-radius: var(--r-md);
  transition: background 0.15s, color 0.15s;
}
.read-more:hover {
  background: var(--accent);
  color: var(--surface);
}
.read-more svg { width: 14px; height: 14px; }

/* =========================================
   INDEX — ARTICLE LIST
   ========================================= */
.section-label {
  font-size: 0.72rem;
  font-weight: 500;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--text-3);
  margin-bottom: var(--sp-6);
}
.article-list { display: flex; flex-direction: column; }
.article-card {
  display: flex;
  gap: var(--sp-4);
  padding: var(--sp-6) 0;
  border-bottom: 1px solid var(--border);
  text-decoration: none;
  color: var(--text);
  transition: none;
}
.article-card:last-child { border-bottom: none; }
.article-card-body { flex: 1; min-width: 0; }
.article-card-tag { margin-bottom: var(--sp-2); }
.article-card-title {
  font-family: var(--serif);
  font-size: 1rem;
  font-weight: 600;
  line-height: 1.5;
  margin-bottom: var(--sp-2);
  color: var(--text);
  transition: color 0.15s;
}
.article-card:hover .article-card-title { color: var(--accent); }
.article-card-desc {
  font-size: 0.82rem;
  color: var(--text-2);
  line-height: 1.65;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
  margin-bottom: var(--sp-3);
}
.article-card-meta { font-size: 0.73rem; color: var(--text-3); }
.article-card-date {
  font-size: 0.72rem;
  color: var(--text-3);
  white-space: nowrap;
  flex-shrink: 0;
  padding-top: 2px;
  line-height: 1.4;
}

/* =========================================
   ARTICLE PAGE — HEADER
   ========================================= */
.article-back {
  display: inline-flex;
  align-items: center;
  gap: var(--sp-2);
  font-size: 0.82rem;
  color: var(--text-2);
  text-decoration: none;
  margin-bottom: var(--sp-8);
  padding: var(--sp-2) 0;
  transition: color 0.15s;
}
.article-back:hover { color: var(--accent); }
.article-back svg { width: 14px; height: 14px; }
.article-header { margin-bottom: var(--sp-10); }
.article-tag-row { display: flex; gap: var(--sp-2); flex-wrap: wrap; margin-bottom: var(--sp-5); }
.article-title {
  font-family: var(--serif);
  font-size: clamp(1.6rem, 6vw, 2.1rem);
  font-weight: 600;
  line-height: 1.4;
  letter-spacing: 0.01em;
  margin-bottom: var(--sp-5);
}
.article-meta {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
  flex-wrap: wrap;
  padding-top: var(--sp-5);
  border-top: 1px solid var(--border);
}
.article-meta .meta-item { font-size: 0.8rem; color: var(--text-3); }

/* =========================================
   ARTICLE PAGE — BODY
   ========================================= */
.article-body {
  font-size: 1rem;
  line-height: 1.95;
  color: var(--text);
}
.article-body > * + * { margin-top: 1.5rem; }
.article-body h2 {
  font-family: var(--serif);
  font-size: 1.2rem;
  font-weight: 600;
  line-height: 1.45;
  margin-top: 2.75rem;
  margin-bottom: 0.75rem;
  padding-bottom: 0.6rem;
  border-bottom: 1px solid var(--border);
  letter-spacing: 0.01em;
}
.article-body h3 {
  font-size: 1rem;
  font-weight: 500;
  line-height: 1.5;
  margin-top: 2rem;
  margin-bottom: 0.4rem;
}
.article-body p { margin-bottom: 0; }
.article-body ul,
.article-body ol {
  padding-left: 1.4rem;
}
.article-body li { margin-bottom: 0.3rem; }
.article-body li::marker { color: var(--text-3); }
.article-body strong { font-weight: 600; }
.article-body em { font-style: italic; }
.article-body a {
  color: var(--accent);
  text-decoration: underline;
  text-underline-offset: 3px;
  text-decoration-color: color-mix(in srgb, var(--accent) 40%, transparent);
}
.article-body a:hover { text-decoration-color: var(--accent); }
.article-body blockquote {
  border-left: 3px solid var(--accent);
  padding: var(--sp-2) 0 var(--sp-2) var(--sp-5);
  color: var(--text-2);
  font-style: italic;
}
.article-body code {
  font-family: var(--mono);
  font-size: 0.85em;
  background: var(--surface-2);
  color: var(--text);
  padding: 0.15em 0.4em;
  border-radius: 4px;
}
.article-body pre {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--r-md);
  padding: var(--sp-5);
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}
.article-body pre code {
  background: none;
  padding: 0;
  font-size: 0.875rem;
  line-height: 1.7;
}

/* =========================================
   TABLE OF CONTENTS
   ========================================= */
.toc {
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  padding: var(--sp-5) var(--sp-6);
  margin: var(--sp-8) 0;
}
.toc-label {
  font-size: 0.72rem;
  font-weight: 500;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--text-3);
  margin-bottom: var(--sp-4);
}
.toc-list {
  list-style: none;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 0.1rem;
}
.toc-list li a {
  display: block;
  font-size: 0.87rem;
  color: var(--text-2);
  text-decoration: none;
  padding: var(--sp-2) 0;
  border-radius: var(--r-sm);
  line-height: 1.5;
  transition: color 0.15s;
}
.toc-list li a:hover { color: var(--accent); }
.toc-list li a::before {
  content: '';
  display: inline-block;
  width: 4px;
  height: 4px;
  border-radius: 50%;
  background: var(--text-3);
  margin-right: var(--sp-3);
  vertical-align: middle;
  flex-shrink: 0;
}

/* =========================================
   READING PROGRESS BAR
   ========================================= */
.progress-bar {
  position: fixed;
  top: 0;
  left: 0;
  height: 2px;
  background: var(--accent);
  width: 0%;
  z-index: 200;
  transition: width 0.1s linear;
}

/* =========================================
   RELATED ARTICLES
   ========================================= */
.related {
  margin-top: var(--sp-12);
  padding-top: var(--sp-10);
  border-top: 1px solid var(--border);
}
.related-label {
  font-size: 0.72rem;
  font-weight: 500;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--text-3);
  margin-bottom: var(--sp-6);
}
.related-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--sp-4);
}
@media (min-width: 500px) {
  .related-grid { grid-template-columns: 1fr 1fr; }
}
.related-card {
  display: flex;
  flex-direction: column;
  gap: var(--sp-2);
  padding: var(--sp-5);
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  text-decoration: none;
  color: var(--text);
  transition: border-color 0.15s, box-shadow 0.15s;
}
.related-card:hover {
  border-color: var(--border-2);
  box-shadow: 0 2px 12px color-mix(in srgb, var(--text) 6%, transparent);
}
.related-card-title {
  font-family: var(--serif);
  font-size: 0.95rem;
  font-weight: 600;
  line-height: 1.5;
  color: var(--text);
  transition: color 0.15s;
}
.related-card:hover .related-card-title { color: var(--accent); }
.related-card-meta { font-size: 0.73rem; color: var(--text-3); }
.related-card-arrow {
  margin-top: auto;
  font-size: 0.78rem;
  color: var(--accent);
  font-weight: 500;
  display: flex;
  align-items: center;
  gap: 4px;
}
.related-card-arrow svg { width: 12px; height: 12px; }

/* =========================================
   NEXT ARTICLE BANNER
   ========================================= */
.next-article {
  margin-top: var(--sp-8);
  padding: var(--sp-6);
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  display: flex;
  align-items: center;
  gap: var(--sp-5);
  text-decoration: none;
  color: var(--text);
  transition: border-color 0.15s;
}
.next-article:hover { border-color: var(--accent); }
.next-article-body { flex: 1; min-width: 0; }
.next-label {
  font-size: 0.7rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-3);
  margin-bottom: var(--sp-1);
}
.next-title {
  font-family: var(--serif);
  font-size: 0.98rem;
  font-weight: 600;
  line-height: 1.45;
  color: var(--text);
  transition: color 0.15s;
}
.next-article:hover .next-title { color: var(--accent); }
.next-arrow {
  color: var(--text-3);
  flex-shrink: 0;
  transition: color 0.15s, transform 0.15s;
}
.next-article:hover .next-arrow {
  color: var(--accent);
  transform: translateX(4px);
}
.next-arrow svg { width: 20px; height: 20px; }

/* =========================================
   FOOTER
   ========================================= */
.site-footer {
  border-top: 1px solid var(--border);
  padding: var(--sp-8) var(--sp-5);
  text-align: center;
}
.site-footer p { font-size: 0.78rem; color: var(--text-3); }
.site-footer a { color: var(--text-2); text-decoration: none; }
.site-footer a:hover { color: var(--accent); }

/* =========================================
   SCROLL TO TOP
   ========================================= */
.scroll-top {
  position: fixed;
  bottom: var(--sp-6);
  right: var(--sp-5);
  width: 42px;
  height: 42px;
  background: var(--surface);
  border: 1px solid var(--border-2);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  color: var(--text-2);
  opacity: 0;
  transform: translateY(8px);
  transition: opacity 0.2s, transform 0.2s, color 0.15s, border-color 0.15s;
  pointer-events: none;
  z-index: 90;
}
.scroll-top.visible {
  opacity: 1;
  transform: translateY(0);
  pointer-events: auto;
}
.scroll-top:hover { color: var(--accent); border-color: var(--accent); }
.scroll-top svg { width: 16px; height: 16px; }

/* =========================================
   UTILITIES
   ========================================= */
.sr-only {
  position: absolute;
  width: 1px; height: 1px;
  padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0,0,0,0);
  white-space: nowrap; border: 0;
}