:root {
  --bg: #f5f5f7;
  --surface: #ffffff;
  --text: #1d1d1f;
  --text-secondary: #6e6e73;
  --link: #0071e3;
  --link-hover: #0077ed;
  --border: #d2d2d7;
  --border-light: #e8e8ed;
  --tag-bg: #f0f1ff;
  --tag-text: #5856d6;
  --tag-hover: #e4e3ff;
  --accent: #0071e3;
  --accent-light: #e8f4fd;
  --header-bg: rgba(255, 255, 255, 0.72);
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.06);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.08);
  --shadow-lg: 0 8px 30px rgba(0, 0, 0, 0.12);
  --radius: 12px;
  --radius-sm: 8px;
  --transition: 0.2s cubic-bezier(0.25, 0.1, 0.25, 1);
}

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

body {
  font-family: "Hiragino Kaku Gothic ProN", "Noto Sans JP", "Yu Gothic", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.8;
  font-size: 15px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* ── Header ── */
header {
  background: var(--header-bg);
  backdrop-filter: saturate(180%) blur(20px);
  -webkit-backdrop-filter: saturate(180%) blur(20px);
  border-bottom: 1px solid var(--border-light);
  padding: 0 24px;
  position: sticky;
  top: 0;
  z-index: 100;
  height: 52px;
}

header nav {
  max-width: 1120px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  gap: 24px;
  height: 100%;
}

.site-title {
  font-weight: 700;
  font-size: 17px;
  text-decoration: none;
  color: var(--text);
  letter-spacing: -0.02em;
}

header nav a {
  color: var(--text);
  text-decoration: none;
  font-size: 14px;
  font-weight: 500;
  opacity: 0.7;
  transition: opacity var(--transition);
}

header nav a:hover {
  opacity: 1;
}

/* ── Layout ── */
.layout {
  max-width: 1120px;
  margin: 0 auto;
  display: flex;
  gap: 28px;
  padding: 28px 24px;
}

main {
  flex: 1;
  min-width: 0;
}

/* ── Headings ── */
h1 {
  font-size: 1.5em;
  font-weight: 700;
  margin-bottom: 20px;
  padding-bottom: 12px;
  border-bottom: none;
  letter-spacing: -0.02em;
  color: var(--text);
}

/* ── Post list ── */
.post-list { list-style: none; }

.post-list li {
  padding: 14px 16px;
  margin-bottom: 6px;
  background: var(--surface);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-sm);
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px;
  transition: box-shadow var(--transition), border-color var(--transition);
}

.post-list li:hover {
  box-shadow: var(--shadow-sm);
  border-color: var(--border);
}

.post-list li a {
  color: var(--text);
  text-decoration: none;
  font-weight: 500;
  transition: color var(--transition);
}

.post-list li a:hover {
  color: var(--link);
}

/* ── Tags ── */
.tag {
  display: inline-block;
  background: var(--tag-bg);
  color: var(--tag-text);
  font-size: 11px;
  font-weight: 500;
  padding: 3px 10px;
  border-radius: 20px;
  text-decoration: none;
  white-space: nowrap;
  transition: background var(--transition), transform var(--transition);
}

.tag:hover {
  background: var(--tag-hover);
  transform: translateY(-1px);
}

.tags { margin-bottom: 20px; display: flex; flex-wrap: wrap; gap: 8px; }
.tags-inline { display: inline-flex; flex-wrap: wrap; gap: 5px; }

.tag-list {
  list-style: none;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 8px;
}

.tag-list li {
  padding: 10px 14px;
  background: var(--surface);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-sm);
  transition: box-shadow var(--transition), border-color var(--transition);
}

.tag-list li:hover {
  box-shadow: var(--shadow-sm);
  border-color: var(--border);
}

.tag-list li a {
  color: var(--text);
  text-decoration: none;
  font-weight: 500;
}

.tag-list li a:hover {
  color: var(--link);
}

.tag-list .count {
  color: var(--text-secondary);
  font-size: 13px;
  margin-left: 4px;
}

/* ── Pagination ── */
.pagination {
  margin: 32px 0 8px;
  display: flex;
  justify-content: center;
  gap: 6px;
  flex-wrap: wrap;
}

.pagination a, .pagination .current {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 40px;
  height: 40px;
  padding: 0 14px;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-sm);
  text-decoration: none;
  color: var(--text);
  font-size: 14px;
  font-weight: 500;
  background: var(--surface);
  transition: all var(--transition);
}

.pagination a:hover {
  border-color: var(--accent);
  color: var(--accent);
  box-shadow: var(--shadow-sm);
}

.pagination .current {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
}

/* ── Month TOC ── */
.month-toc {
  background: var(--surface);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-sm);
  padding: 16px 20px;
  margin-bottom: 24px;
}

.month-toc ul {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: 6px 12px;
}

.month-toc li a {
  color: var(--text);
  text-decoration: none;
  font-size: 14px;
  font-weight: 500;
  transition: color var(--transition);
}

.month-toc li a:hover {
  color: var(--link);
}

/* ── Post detail ── */
.post-full + hr {
  border: none;
  border-top: 1px solid var(--border-light);
  margin: 32px 0;
}

.post-full h1 {
  font-size: 1.6em;
  margin-bottom: 16px;
}

.post-full h1 a {
  color: var(--text);
  text-decoration: none;
  transition: color var(--transition);
}

.post-full h1 a:hover {
  color: var(--link);
}

.post-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 24px;
  padding: 12px 16px;
  background: var(--surface);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-sm);
  font-size: 14px;
}

.post-nav a {
  color: var(--link);
  text-decoration: none;
  font-weight: 500;
  transition: opacity var(--transition);
}

.post-nav a:hover { opacity: 0.7; }

.post-content {
  overflow-wrap: break-word;
  background: var(--surface);
  border: 1px solid var(--border-light);
  border-radius: var(--radius);
  padding: 28px 24px;
}

.post-content h2 {
  font-size: 1.2em;
  font-weight: 700;
  margin: 32px 0 12px;
  padding-bottom: 8px;
  border-bottom: 2px solid var(--border-light);
  color: var(--text);
}

.post-content h2:first-child {
  margin-top: 0;
}

.post-content h3 {
  font-size: 1.05em;
  font-weight: 600;
  margin: 20px 0 8px;
  color: var(--text);
}

.post-content ul, .post-content ol { margin: 10px 0 10px 24px; }
.post-content p { margin: 10px 0; }

.post-content blockquote {
  max-width: 100%;
  margin: 16px 0;
  white-space: pre-wrap;
}

.post-content a {
  color: var(--link);
  text-decoration: none;
  transition: opacity var(--transition);
}

.post-content a:hover { opacity: 0.7; }

/* ── Footer ── */
footer {
  text-align: center;
  padding: 32px 24px;
  color: var(--text-secondary);
  font-size: 13px;
  border-top: 1px solid var(--border-light);
  margin-top: 48px;
}

/* ── Month navigation sidebar ── */
.month-nav {
  width: 210px;
  flex-shrink: 0;
  position: sticky;
  top: 68px;
  align-self: flex-start;
  max-height: calc(100vh - 84px);
  overflow-y: auto;
  font-size: 13px;
  background: var(--surface);
  border: 1px solid var(--border-light);
  border-radius: var(--radius);
  padding: 16px;
  box-shadow: var(--shadow-sm);
}

.month-nav::-webkit-scrollbar {
  width: 4px;
}

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

.month-nav h2 {
  font-size: 13px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-secondary);
  margin-bottom: 12px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--border-light);
}

.month-nav details {
  margin-bottom: 2px;
}

.month-nav summary {
  cursor: pointer;
  font-weight: 600;
  padding: 6px 8px;
  border-radius: 6px;
  user-select: none;
  transition: background var(--transition), color var(--transition);
  list-style: none;
}

.month-nav summary::-webkit-details-marker { display: none; }

.month-nav summary::before {
  content: "›";
  display: inline-block;
  margin-right: 6px;
  font-size: 14px;
  font-weight: 700;
  transition: transform var(--transition);
  color: var(--text-secondary);
}

.month-nav details[open] > summary::before {
  transform: rotate(90deg);
}

.month-nav summary:hover {
  background: var(--accent-light);
  color: var(--link);
}

.month-links {
  display: flex;
  flex-wrap: wrap;
  gap: 4px;
  padding: 6px 4px 6px 20px;
}

.month-links a {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 4px 8px;
  border-radius: 6px;
  text-decoration: none;
  color: var(--text-secondary);
  font-size: 12px;
  font-weight: 500;
  transition: all var(--transition);
}

.month-links a:hover {
  background: var(--accent-light);
  color: var(--link);
}

.month-links a.active {
  background: var(--accent);
  color: #fff;
  font-weight: 600;
}

/* ── Back links ── */
main > p:last-child a {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  color: var(--link);
  text-decoration: none;
  font-weight: 500;
  font-size: 14px;
  padding: 8px 0;
  transition: opacity var(--transition);
}

main > p:last-child a:hover {
  opacity: 0.7;
}

/* ── Responsive ── */
@media (max-width: 768px) {
  header { padding: 0 16px; }

  .layout {
    flex-direction: column;
    padding: 16px;
    gap: 16px;
  }

  .month-nav {
    width: 100%;
    position: static;
    max-height: none;
    order: -1;
  }

  .tag-list {
    grid-template-columns: 1fr;
  }

  .post-nav { font-size: 13px; }

  h1 { font-size: 1.3em; }

  .post-content {
    padding: 20px 16px;
    border-radius: var(--radius-sm);
  }

  .post-list li {
    padding: 12px;
  }
}