/* =========================================================
   Research Notes — TECH DARK THEME Stylesheet
   =========================================================
   Palette: near-black bg · dark surface cards · electric cyan
   accent · subtle grid lines · monospace code aesthetic
   ========================================================= */

/* ---------------------------------------------------------
   1. CSS Custom Properties
   --------------------------------------------------------- */
:root {
  /* Dark background stack */
  --color-bg:           #0a0c10;
  --color-bg-2:         #0f1117;
  --color-surface:      #13161e;
  --color-surface-2:    #1a1e28;
  --color-border:       #232733;
  --color-border-hi:    #2e3447;

  /* Text */
  --color-text:         #e8eaf0;
  --color-text-2:       #b0b8cc;
  --color-text-muted:   #5c6480;

  /* Accent — electric cyan / teal */
  --color-accent:       #00d4ff;
  --color-accent-2:     #00aacc;
  --color-accent-dim:   rgba(0, 212, 255, .10);
  --color-accent-glow:  rgba(0, 212, 255, .22);

  /* Secondary accent — subtle violet */
  --color-violet:       #7c6aff;
  --color-violet-dim:   rgba(124, 106, 255, .12);

  /* Green for success / theorem */
  --color-green:        #00e5a0;
  --color-green-dim:    rgba(0, 229, 160, .10);

  /* Orange for warning / remark */
  --color-orange:       #ff9e3d;
  --color-orange-dim:   rgba(255, 158, 61, .10);

  /* Typography */
  --font-display: 'Space Grotesk', 'Inter', system-ui, sans-serif;
  --font-body:    'Inter', system-ui, sans-serif;
  --font-mono:    'JetBrains Mono', 'Fira Code', 'Cascadia Code', monospace;

  /* Sizing */
  --container-max:  1120px;
  --sidebar-width:  300px;
  --gap:            1.75rem;
  --radius:         8px;
  --radius-sm:      5px;
  --radius-lg:      12px;

  /* Shadows / glows */
  --shadow-card:    0 1px 3px rgba(0,0,0,.5), 0 0 0 1px var(--color-border);
  --shadow-hover:   0 4px 24px rgba(0,0,0,.6), 0 0 0 1px var(--color-border-hi), 0 0 20px var(--color-accent-glow);
  --shadow-accent:  0 0 30px var(--color-accent-glow);

  /* Transitions */
  --transition:     0.18s ease;
  --transition-slow: 0.32s ease;
}

/* ---------------------------------------------------------
   2. Reset & Base
   --------------------------------------------------------- */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  background-color: var(--color-bg);
  color: var(--color-text);
  font-family: var(--font-body);
  font-weight: 400;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
  /* Subtle dot-grid background */
  background-image: radial-gradient(circle, #1e2235 1px, transparent 1px);
  background-size: 28px 28px;
}

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

a {
  color: var(--color-accent);
  text-decoration: none;
  transition: color var(--transition);
}
a:hover { color: #fff; }

ul, ol { padding-left: 1.5rem; }

/* Selection */
::selection {
  background: var(--color-accent);
  color: #000;
}

/* ---------------------------------------------------------
   3. Typography
   --------------------------------------------------------- */
h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-display);
  font-weight: 700;
  line-height: 1.2;
  color: var(--color-text);
  letter-spacing: -0.01em;
}

h1 { font-size: clamp(1.9rem, 4vw, 2.6rem); }
h2 { font-size: clamp(1.25rem, 2.5vw, 1.6rem); }
h3 { font-size: 1.1rem; }
h4 { font-size: 0.95rem; }

p { margin-bottom: 1rem; }
p:last-child { margin-bottom: 0; }

/* Inline code */
code {
  font-family: var(--font-mono);
  font-size: 0.82em;
  background: var(--color-surface-2);
  border: 1px solid var(--color-border);
  padding: 0.15em 0.45em;
  border-radius: 4px;
  color: var(--color-accent);
}

/* Code blocks */
pre {
  background: #080b10;
  border: 1px solid var(--color-border);
  border-left: 3px solid var(--color-accent);
  padding: 1.25rem 1.5rem;
  border-radius: var(--radius);
  overflow-x: auto;
  margin: 1.5rem 0;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  line-height: 1.65;
  color: #c9d1e8;
}

pre code {
  background: none;
  border: none;
  color: inherit;
  padding: 0;
  font-size: inherit;
}

blockquote {
  border-left: 3px solid var(--color-accent);
  background: var(--color-accent-dim);
  padding: 1rem 1.5rem;
  border-radius: 0 var(--radius) var(--radius) 0;
  margin: 1.5rem 0;
  font-style: italic;
  color: var(--color-text-2);
}

hr {
  border: none;
  border-top: 1px solid var(--color-border);
  margin: 2rem 0;
}

/* KaTeX */
.katex-display {
  margin: 1.5rem 0;
  overflow-x: auto;
  overflow-y: hidden;
  padding: 1rem 1.25rem;
  background: var(--color-surface-2);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
}

.katex { color: var(--color-text); }

/* ---------------------------------------------------------
   4. Layout
   --------------------------------------------------------- */
.container {
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 1.5rem;
}

.content-layout {
  display: grid;
  grid-template-columns: 1fr var(--sidebar-width);
  gap: var(--gap);
  align-items: start;
  padding: 2.5rem 0 5rem;
}

.posts-column { min-width: 0; }

/* ---------------------------------------------------------
   5. Site Header
   --------------------------------------------------------- */
.site-header {
  background: var(--color-bg-2);
  border-bottom: 1px solid var(--color-border);
  padding: 2.25rem 0 1.75rem;
  text-align: center;
  position: relative;
  overflow: hidden;
}

/* Glowing horizontal line across top */
.site-header::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 2px;
  background: linear-gradient(90deg, transparent 0%, var(--color-accent) 30%, var(--color-violet) 70%, transparent 100%);
}

.site-header::after {
  content: '';
  position: absolute;
  top: 0; left: 50%;
  transform: translateX(-50%);
  width: 400px;
  height: 120px;
  background: radial-gradient(ellipse at top, rgba(0,212,255,.08) 0%, transparent 70%);
  pointer-events: none;
}

.site-branding {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.4rem;
  position: relative;
  z-index: 1;
}

/* Monospace label above title */
.site-label {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--color-accent);
  letter-spacing: 0.18em;
  text-transform: uppercase;
  opacity: 0.85;
  margin-bottom: 0.25rem;
}

.site-title {
  font-family: var(--font-display);
  font-size: clamp(2rem, 5vw, 3rem);
  font-weight: 700;
  letter-spacing: -0.03em;
}

.site-title a {
  color: var(--color-text);
  background: linear-gradient(135deg, #e8eaf0 30%, var(--color-accent) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.site-title a:hover {
  -webkit-text-fill-color: transparent;
}

.site-tagline {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  color: var(--color-text-muted);
  letter-spacing: 0.06em;
  text-transform: uppercase;
  margin: 0;
}

/* Typing cursor — added/removed by JS, no inline styles */
.site-tagline.typing-cursor {
  display: inline-block;
  border-right: 2px solid var(--color-accent);
  padding-right: 2px;
}
.site-tagline.typing-cursor.cursor-hidden {
  border-right-color: transparent;
}

/* ---------------------------------------------------------
   6. Primary Navigation
   --------------------------------------------------------- */
.primary-nav {
  background: rgba(15, 17, 23, 0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border);
  position: sticky;
  top: 0;
  z-index: 100;
}

.primary-nav .container {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 50px;
  position: relative;
}

.nav-menu {
  list-style: none;
  padding: 0;
  margin: 0;
  display: flex;
  align-items: center;
}

.nav-menu li a {
  display: block;
  padding: 0.8rem 1.1rem;
  color: var(--color-text-muted);
  font-family: var(--font-mono);
  font-weight: 400;
  font-size: 0.78rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  transition: color var(--transition);
  position: relative;
}

.nav-menu li a::after {
  content: '';
  position: absolute;
  bottom: 0; left: 1.1rem; right: 1.1rem;
  height: 2px;
  background: var(--color-accent);
  transform: scaleX(0);
  transition: transform var(--transition);
  border-radius: 2px;
}

.nav-menu li a:hover,
.nav-menu li a.active {
  color: var(--color-accent);
}

.nav-menu li a:hover::after,
.nav-menu li a.active::after {
  transform: scaleX(1);
}

/* Hamburger */
.nav-toggle {
  display: none;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  background: none;
  border: none;
  cursor: pointer;
  padding: 0.5rem;
  position: absolute;
  right: 1.5rem;
}

.nav-toggle span {
  display: block;
  width: 20px;
  height: 1.5px;
  background: var(--color-text-muted);
  border-radius: 2px;
  transition: transform var(--transition), opacity var(--transition);
}

.nav-toggle[aria-expanded="true"] span:nth-child(1) { transform: translateY(6.5px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] span:nth-child(2) { opacity: 0; }
.nav-toggle[aria-expanded="true"] span:nth-child(3) { transform: translateY(-6.5px) rotate(-45deg); }

/* ---------------------------------------------------------
   7. Post Cards
   --------------------------------------------------------- */
.post-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 1.75rem 2rem;
  margin-bottom: 1.25rem;
  transition: border-color var(--transition), box-shadow var(--transition), transform var(--transition);
  position: relative;
  overflow: hidden;
}

/* Accent left edge on hover */
.post-card::before {
  content: '';
  position: absolute;
  left: 0; top: 0; bottom: 0;
  width: 3px;
  background: linear-gradient(180deg, var(--color-accent), var(--color-violet));
  opacity: 0;
  transition: opacity var(--transition);
  border-radius: 3px 0 0 3px;
}

.post-card:hover {
  border-color: var(--color-border-hi);
  box-shadow: var(--shadow-hover);
  transform: translateY(-2px);
}

.post-card:hover::before { opacity: 1; }

.post-card-header { margin-bottom: 0.85rem; }

.post-meta {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin-bottom: 0.5rem;
}

.post-meta time,
.post-meta .author-link {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--color-text-muted);
  letter-spacing: 0.04em;
}

.post-meta .author-link:hover { color: var(--color-accent); }

.meta-sep { color: var(--color-border-hi); font-size: 0.8rem; }

.post-title {
  font-size: clamp(1.15rem, 2vw, 1.4rem);
  font-weight: 700;
  line-height: 1.3;
  letter-spacing: -0.02em;
}

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

.post-excerpt {
  font-size: 0.92rem;
  color: var(--color-text-2);
  line-height: 1.78;
  margin-bottom: 1.1rem;
}

.post-excerpt p { margin-bottom: 0.65rem; }

.post-card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.65rem;
  padding-top: 1rem;
  border-top: 1px solid var(--color-border);
}

/* Read-more button */
.btn-read-more {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  background: transparent;
  color: var(--color-accent);
  border: 1px solid var(--color-accent);
  font-family: var(--font-mono);
  font-weight: 400;
  font-size: 0.72rem;
  padding: 0.4rem 0.95rem;
  border-radius: 4px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  transition: background var(--transition), color var(--transition), box-shadow var(--transition);
}

.btn-read-more::after { content: ' →'; }

.btn-read-more:hover {
  background: var(--color-accent);
  color: #000;
  box-shadow: 0 0 14px var(--color-accent-glow);
}

/* Tags */
.post-tags { display: flex; flex-wrap: wrap; gap: 0.35rem; }

.tag {
  display: inline-block;
  padding: 0.18rem 0.6rem;
  background: var(--color-surface-2);
  color: var(--color-text-muted);
  font-family: var(--font-mono);
  font-size: 0.68rem;
  border-radius: 3px;
  border: 1px solid var(--color-border);
  letter-spacing: 0.04em;
  transition: border-color var(--transition), color var(--transition);
}

.post-card:hover .tag {
  border-color: var(--color-border-hi);
  color: var(--color-text-2);
}

/* ---------------------------------------------------------
   8. Pagination
   --------------------------------------------------------- */
.pagination {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.4rem;
  padding: 1.75rem 0;
  flex-wrap: wrap;
}

.page-item {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 36px;
  height: 36px;
  padding: 0 0.75rem;
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: 0.78rem;
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  color: var(--color-text-muted);
  transition: all var(--transition);
}

a.page-item:hover {
  border-color: var(--color-accent);
  color: var(--color-accent);
  background: var(--color-accent-dim);
}

.page-item.current {
  background: var(--color-accent-dim);
  border-color: var(--color-accent);
  color: var(--color-accent);
  cursor: default;
}

.page-next { padding: 0 1rem; font-size: 0.72rem; }

/* ---------------------------------------------------------
   9. Sidebar & Widgets
   --------------------------------------------------------- */
.sidebar {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  position: sticky;
  top: 70px;
}

.widget {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 1.25rem 1.4rem;
  overflow: hidden;
  position: relative;
}

/* Accent top line on widget */
.widget::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--color-accent), var(--color-violet));
  opacity: 0.6;
}

.widget-title {
  font-family: var(--font-mono);
  font-size: 0.68rem;
  font-weight: 400;
  text-transform: uppercase;
  letter-spacing: 0.14em;
  color: var(--color-accent);
  padding-bottom: 0.6rem;
  margin-bottom: 0.85rem;
  border-bottom: 1px solid var(--color-border);
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.widget-title::before {
  content: '//';
  opacity: 0.5;
}

/* About widget */
.widget-about p {
  font-size: 0.845rem;
  line-height: 1.72;
  color: var(--color-text-2);
}

.widget-about strong { color: var(--color-text); }

.widget-links {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin-top: 0.85rem;
}

.widget-link-btn {
  display: inline-block;
  padding: 0.28rem 0.75rem;
  background: var(--color-surface-2);
  color: var(--color-text-2);
  font-family: var(--font-mono);
  font-size: 0.7rem;
  border-radius: 3px;
  border: 1px solid var(--color-border);
  letter-spacing: 0.06em;
  text-transform: uppercase;
  transition: all var(--transition);
}

.widget-link-btn:hover {
  border-color: var(--color-accent);
  color: var(--color-accent);
  background: var(--color-accent-dim);
}

/* Search */
.search-form {
  display: flex;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  overflow: hidden;
  transition: border-color var(--transition), box-shadow var(--transition);
}

.search-form:focus-within {
  border-color: var(--color-accent);
  box-shadow: 0 0 0 3px var(--color-accent-dim);
}

.search-input {
  flex: 1;
  border: none;
  padding: 0.55rem 0.85rem;
  font-family: var(--font-mono);
  font-size: 0.8rem;
  background: var(--color-surface-2);
  color: var(--color-text);
  outline: none;
  letter-spacing: 0.02em;
}

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

.search-btn {
  background: var(--color-surface-2);
  border: none;
  border-left: 1px solid var(--color-border);
  padding: 0 0.75rem;
  cursor: pointer;
  color: var(--color-text-muted);
  display: flex;
  align-items: center;
  transition: color var(--transition), background var(--transition);
}

.search-btn:hover {
  background: var(--color-accent-dim);
  color: var(--color-accent);
}

/* Recent posts */
.recent-posts-list {
  list-style: none;
  padding: 0;
  margin: 0;
}

.recent-posts-list li {
  display: flex;
  flex-direction: column;
  gap: 0.1rem;
  padding: 0.55rem 0;
  border-bottom: 1px solid var(--color-border);
}

.recent-posts-list li:last-child {
  border-bottom: none;
  padding-bottom: 0;
}

.recent-posts-list a {
  font-size: 0.82rem;
  font-weight: 500;
  line-height: 1.4;
  color: var(--color-text-2);
}

.recent-posts-list a:hover { color: var(--color-accent); }

.rp-date {
  font-family: var(--font-mono);
  font-size: 0.68rem;
  color: var(--color-text-muted);
}

/* Tags cloud */
.tag-cloud { display: flex; flex-wrap: wrap; gap: 0.35rem; }

.tag-link {
  display: inline-block;
  padding: 0.22rem 0.65rem;
  background: var(--color-surface-2);
  color: var(--color-text-muted);
  font-family: var(--font-mono);
  font-size: 0.68rem;
  border-radius: 3px;
  border: 1px solid var(--color-border);
  letter-spacing: 0.04em;
  transition: all var(--transition);
}

.tag-link:hover {
  border-color: var(--color-accent);
  color: var(--color-accent);
  background: var(--color-accent-dim);
}

/* Archives */
.archives-list {
  list-style: none;
  padding: 0;
  margin: 0;
}

.archives-list li {
  padding: 0.45rem 0;
  border-bottom: 1px solid var(--color-border);
}

.archives-list li:last-child { border-bottom: none; }

.archives-list a {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--color-text-2);
}

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

.archive-count {
  color: var(--color-text-muted);
  font-size: 0.72rem;
}

/* ---------------------------------------------------------
   10. About Page
   --------------------------------------------------------- */
.about-layout {
  max-width: 840px;
  margin: 0 auto;
  padding: 2.5rem 0 5rem;
}

.about-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 2.25rem 2.5rem;
  margin-bottom: 1.25rem;
  position: relative;
  overflow: hidden;
}

.about-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--color-accent), var(--color-violet));
}

.about-header {
  display: flex;
  align-items: center;
  gap: 1.75rem;
  margin-bottom: 1.75rem;
  flex-wrap: wrap;
}

.about-avatar {
  width: 90px;
  height: 90px;
  border-radius: var(--radius);
  background: var(--color-surface-2);
  border: 1px solid var(--color-accent);
  box-shadow: 0 0 20px var(--color-accent-glow);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-mono);
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--color-accent);
  flex-shrink: 0;
  letter-spacing: 0.05em;
}

.about-intro h1 {
  font-size: clamp(1.5rem, 3vw, 2rem);
  margin-bottom: 0.3rem;
  background: linear-gradient(135deg, #e8eaf0 40%, var(--color-accent));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.about-role {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  color: var(--color-text-muted);
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.about-body h2 {
  font-size: 1rem;
  font-family: var(--font-mono);
  font-weight: 400;
  color: var(--color-accent);
  margin: 1.75rem 0 0.65rem;
  padding-bottom: 0.4rem;
  border-bottom: 1px solid var(--color-border);
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.about-body h2::before { content: '// '; opacity: 0.5; }

.about-body p,
.about-body ul {
  font-size: 0.92rem;
  line-height: 1.8;
  color: var(--color-text-2);
}

.about-body ul li { margin-bottom: 0.45rem; }
.about-body strong { color: var(--color-text); }
.about-body a { color: var(--color-accent); }
.about-body em { color: var(--color-text); font-style: italic; }

/* Links grid */
.links-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(175px, 1fr));
  gap: 0.65rem;
  margin-top: 0.85rem;
}

.link-card {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  padding: 0.75rem 0.9rem;
  background: var(--color-surface-2);
  border-radius: var(--radius-sm);
  border: 1px solid var(--color-border);
  font-family: var(--font-mono);
  font-size: 0.78rem;
  color: var(--color-text-2);
  transition: all var(--transition);
}

.link-card:hover {
  border-color: var(--color-accent);
  color: var(--color-accent);
  background: var(--color-accent-dim);
  transform: translateY(-1px);
}

.link-card .link-icon {
  width: 28px;
  height: 28px;
  background: var(--color-border);
  border-radius: 4px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--color-text-muted);
  font-size: 0.68rem;
  font-family: var(--font-mono);
  flex-shrink: 0;
  letter-spacing: 0;
}

.link-card:hover .link-icon {
  background: var(--color-accent-dim);
  color: var(--color-accent);
}

/* Contact form */
.contact-form {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  margin-top: 1rem;
}

.form-group {
  display: flex;
  flex-direction: column;
  gap: 0.3rem;
}

.form-group label {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.1em;
}

.form-group input,
.form-group textarea {
  padding: 0.65rem 0.9rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  font-family: var(--font-body);
  font-size: 0.9rem;
  background: var(--color-surface-2);
  color: var(--color-text);
  outline: none;
  transition: border-color var(--transition), box-shadow var(--transition);
}

.form-group input:focus,
.form-group textarea:focus {
  border-color: var(--color-accent);
  box-shadow: 0 0 0 3px var(--color-accent-dim);
}

.form-group textarea {
  min-height: 120px;
  resize: vertical;
}

.btn-submit {
  align-self: flex-start;
  background: transparent;
  color: var(--color-accent);
  border: 1px solid var(--color-accent);
  padding: 0.6rem 1.5rem;
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: 0.78rem;
  cursor: pointer;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  transition: all var(--transition);
}

.btn-submit:hover {
  background: var(--color-accent);
  color: #000;
  box-shadow: 0 0 18px var(--color-accent-glow);
}

/* ---------------------------------------------------------
   11. Blog Index
   --------------------------------------------------------- */
.page-heading { margin-bottom: 1.75rem; }

.page-heading h1 {
  font-size: clamp(1.6rem, 3vw, 2.1rem);
  margin-bottom: 0.3rem;
}

.page-heading p {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  color: var(--color-text-muted);
  letter-spacing: 0.04em;
}

.filter-bar {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin-bottom: 1.5rem;
  align-items: center;
}

.filter-label {
  font-family: var(--font-mono);
  font-size: 0.68rem;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-right: 0.2rem;
}

.filter-btn {
  padding: 0.25rem 0.75rem;
  border: 1px solid var(--color-border);
  border-radius: 3px;
  background: var(--color-surface);
  font-family: var(--font-mono);
  font-size: 0.7rem;
  cursor: pointer;
  transition: all var(--transition);
  color: var(--color-text-muted);
  letter-spacing: 0.06em;
}

.filter-btn:hover,
.filter-btn.active {
  background: var(--color-accent-dim);
  border-color: var(--color-accent);
  color: var(--color-accent);
}

/* ---------------------------------------------------------
   12. Single Post Page
   --------------------------------------------------------- */
.post-layout {
  display: grid;
  grid-template-columns: 1fr var(--sidebar-width);
  gap: var(--gap);
  align-items: start;
  padding: 2.5rem 0 5rem;
}

.post-article {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 2.25rem 2.5rem;
  position: relative;
  overflow: hidden;
}

.post-article::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--color-accent), var(--color-violet));
}

.post-article-header {
  margin-bottom: 2rem;
  padding-bottom: 1.5rem;
  border-bottom: 1px solid var(--color-border);
}

.post-article-header h1 {
  font-size: clamp(1.5rem, 3vw, 2rem);
  line-height: 1.2;
  margin-bottom: 0.85rem;
  letter-spacing: -0.025em;
}

.post-article-tags { display: flex; flex-wrap: wrap; gap: 0.4rem; margin-top: 0.75rem; }

.back-link {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--color-text-muted);
  letter-spacing: 0.06em;
  text-transform: uppercase;
  margin-bottom: 1.25rem;
  transition: color var(--transition);
}

.back-link:hover { color: var(--color-accent); }

/* Post body content */
.post-content {
  font-size: 0.975rem;
  line-height: 1.88;
  color: var(--color-text-2);
}

.post-content h2 {
  font-size: 1.3rem;
  margin: 2.25rem 0 0.65rem;
  color: var(--color-text);
  padding-bottom: 0.4rem;
  border-bottom: 1px solid var(--color-border);
}

.post-content h3 {
  font-size: 1.05rem;
  margin: 1.75rem 0 0.5rem;
  color: var(--color-text);
}

.post-content p { margin-bottom: 1.1rem; }
.post-content a {
  color: var(--color-accent);
  text-underline-offset: 3px;
  text-decoration: underline;
  text-decoration-color: var(--color-accent-dim);
}
.post-content a:hover {
  color: #fff;
  text-decoration-color: var(--color-accent);
}

.post-content ul, .post-content ol { margin-bottom: 1.1rem; }
.post-content li { margin-bottom: 0.4rem; }

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

/* ── Conjecture / highlight box ── */
.conjecture-box {
  border-left: 3px solid var(--color-accent);
  border-right: 1px solid var(--color-border);
  border-top: 1px solid var(--color-border);
  border-bottom: 1px solid var(--color-border);
  border-radius: 0 var(--radius) var(--radius) 0;
  background: color-mix(in srgb, var(--color-accent) 6%, var(--color-bg-card));
  padding: 1.1rem 1.4rem;
  margin: 1.6rem 0;
}
.conjecture-box p {
  margin: 0 0 0.75rem;
  line-height: 1.75;
  font-style: italic;
  color: var(--color-text);
}
.conjecture-box p:last-child {
  margin-bottom: 0;
}

/* ── References list ── */
/* ── Updates list ── */
.updates-list {
  list-style: none;
  padding: 0;
  margin: 0.5rem 0 1.5rem;
}
.updates-list li {
  display: flex;
  gap: 0.75rem;
  align-items: baseline;
  padding: 0.55rem 0;
  border-bottom: 1px solid var(--color-border);
  font-size: 0.9rem;
  line-height: 1.65;
}
.updates-list li:last-child { border-bottom: none; }
.update-date {
  flex-shrink: 0;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  color: var(--color-accent);
  font-weight: 600;
  min-width: 5.5rem;
}

.references-list {
  font-size: 0.86rem;
  line-height: 1.85;
  color: var(--color-text-2);
  padding-left: 1.5rem;
}
.references-list li {
  margin-bottom: 0.55rem;
}
.references-list a {
  color: var(--color-accent);
  word-break: break-all;
}

/* ── Figure / image ── */
.post-figure {
  margin: 2rem 0 1.6rem;
  text-align: center;
}
.post-figure img {
  width: 100%;
  max-width: 720px;
  border-radius: var(--radius);
  border: 1px solid var(--color-border);
  background: var(--color-bg-card);
  min-height: 40px;
}
.post-figure.is-small img { max-width: 50%; margin-left: auto; margin-right: auto; }
/* Graceful placeholder when an image hasn't been uploaded yet */
.post-figure img[src=""], .post-figure img:not([src]) {
  min-height: 120px;
}
.post-figure figcaption {
  margin-top: 0.65rem;
  font-size: 0.82rem;
  color: var(--color-text-muted);
  line-height: 1.55;
  max-width: 620px;
  margin-left: auto;
  margin-right: auto;
  font-style: italic;
}
.post-figure figcaption strong {
  font-style: normal;
  color: var(--color-accent);
}

/* Two figures side by side; stacks on narrow screens */
.post-figure-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
  align-items: start;
  margin: 2rem 0 1.6rem;
}
.post-figure-row.cols-3 { grid-template-columns: repeat(3, 1fr); }
.post-figure-row .post-figure { margin: 0; }
@media (max-width: 640px) {
  .post-figure-row, .post-figure-row.cols-3 { grid-template-columns: 1fr; gap: 1.6rem; }
  .post-figure.is-small img { max-width: 100%; }
}

/* Callout boxes */
.box-theorem,
.box-definition,
.box-remark {
  border-radius: var(--radius);
  padding: 1.1rem 1.35rem;
  margin: 1.5rem 0;
  border-left: 3px solid;
  border-top: 1px solid;
  border-right: 1px solid;
  border-bottom: 1px solid;
}

.box-theorem {
  background: var(--color-accent-dim);
  border-left-color: var(--color-accent);
  border-color: rgba(0,212,255,.2);
  border-left-color: var(--color-accent);
}

.box-definition {
  background: var(--color-green-dim);
  border-color: rgba(0,229,160,.2);
  border-left-color: var(--color-green);
}

.box-remark {
  background: var(--color-orange-dim);
  border-color: rgba(255,158,61,.2);
  border-left-color: var(--color-orange);
}

.box-label {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.4rem;
  display: block;
}

.box-theorem .box-label { color: var(--color-accent); }
.box-definition .box-label { color: var(--color-green); }
.box-remark .box-label { color: var(--color-orange); }

/* Post navigation */
.post-nav {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
  margin-top: 2.5rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--color-border);
}

.post-nav-link {
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
  padding: 0.85rem 1rem;
  background: var(--color-surface-2);
  border-radius: var(--radius-sm);
  border: 1px solid var(--color-border);
  transition: all var(--transition);
}

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

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

.post-nav-direction {
  font-family: var(--font-mono);
  font-size: 0.68rem;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

.post-nav-title {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-text-2);
  line-height: 1.35;
}

.post-nav-link:hover .post-nav-title { color: var(--color-accent); }
.post-nav-link:hover .post-nav-direction { color: var(--color-text-muted); }

/* Reading progress bar */
#reading-progress {
  background: linear-gradient(90deg, var(--color-accent), var(--color-violet)) !important;
}

/* ---------------------------------------------------------
   13. Footer
   --------------------------------------------------------- */
.site-footer {
  background: var(--color-bg-2);
  border-top: 1px solid var(--color-border);
  padding: 2rem 0;
}

.site-footer .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 1rem;
}

.footer-text {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--color-text-muted);
  letter-spacing: 0.04em;
  margin: 0;
}

.footer-nav { display: flex; gap: 1.5rem; flex-wrap: wrap; }

.footer-nav a {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--color-text-muted);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  transition: color var(--transition);
}

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

/* ---------------------------------------------------------
   14. Responsive
   --------------------------------------------------------- */
@media (max-width: 1024px) {
  :root { --sidebar-width: 260px; }
}

@media (max-width: 860px) {
  .content-layout,
  .post-layout {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: static;
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 1rem;
  }

  .widget-about { grid-column: 1 / -1; }
}

@media (max-width: 640px) {
  .nav-toggle { display: flex; }

  .nav-menu {
    display: none;
    flex-direction: column;
    align-items: stretch;
    background: var(--color-bg-2);
    border-bottom: 1px solid var(--color-border);
    position: absolute;
    top: 100%; left: 0; right: 0;
    z-index: 200;
    padding: 0.5rem 0;
  }

  .nav-menu.is-open { display: flex; }

  .nav-menu li a {
    padding: 0.7rem 1.5rem;
    font-size: 0.82rem;
  }

  .nav-menu li a::after { display: none; }

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

  .post-card { padding: 1.3rem 1.25rem; }
  .post-article { padding: 1.5rem 1.25rem; }
  .about-card { padding: 1.5rem 1.25rem; }
  .about-header { flex-direction: column; gap: 1rem; }

  .post-nav { grid-template-columns: 1fr; }
  .post-nav-link.next { text-align: left; }

  .site-footer .container { flex-direction: column; text-align: center; }
  .footer-nav { justify-content: center; }
  .content-layout { padding: 1.5rem 0 3rem; }
}

@media (max-width: 400px) {
  .container { padding: 0 1rem; }
  .site-header { padding: 1.5rem 0 1.25rem; }
}

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

/* Scrollbar styling (webkit) */
::-webkit-scrollbar { width: 8px; height: 8px; }
::-webkit-scrollbar-track { background: var(--color-bg); }
::-webkit-scrollbar-thumb { background: var(--color-border-hi); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: var(--color-accent); }