/* ==========================================================================
   /thinking/ — 技术博客 · 主样式表
   A content-first, responsive design inspired by minimal tech blog aesthetics.
   ========================================================================== */

/* --------------------------------------------------------------------------
   1. CSS Custom Properties
   -------------------------------------------------------------------------- */
:root {
  /* Color palette — neutral, low-saturation, paper-like */
  --color-bg: #fafaf9;
  --color-bg-card: #ffffff;
  --color-bg-code: #f1f5f9;
  --color-bg-hover: #f5f5f4;
  --color-text: #1c1917;
  --color-text-secondary: #78716c;
  --color-text-muted: #a8a29e;
  --color-border: #e7e5e4;
  --color-border-light: #f0efed;
  --color-accent: #2563eb;
  --color-accent-hover: #1d4ed8;
  --color-accent-bg: #eff6ff;
  --color-tag-bg: #f1f5f9;
  --color-tag-text: #475569;

  /* Typography — optimized for Chinese + English screen reading */
  --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'PingFang SC',
    'Hiragino Sans GB', 'Microsoft YaHei', 'Noto Sans CJK SC', 'Helvetica Neue',
    Helvetica, Arial, sans-serif;
  --font-body: 'PingFang SC', 'Microsoft YaHei', 'Noto Sans CJK SC',
    'Hiragino Sans GB', -apple-system, BlinkMacSystemFont, 'Segoe UI',
    'Helvetica Neue', Arial, sans-serif;
  --font-serif: 'Noto Serif SC', 'Source Han Serif SC', 'Source Han Serif CN',
    'Songti SC', Georgia, 'Times New Roman', serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', 'Source Code Pro',
    Consolas, monospace;

  /* Spacing scale */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.25rem;
  --space-6: 1.5rem;
  --space-8: 2rem;
  --space-10: 2.5rem;
  --space-12: 3rem;
  --space-16: 4rem;
  --space-20: 5rem;

  /* Layout */
  --content-max-width: 720px;
  --sidebar-width: 260px;
  --header-height: 56px;

  /* Misc */
  --radius: 6px;
  --radius-sm: 4px;
  --radius-lg: 10px;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.04);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.06);
  --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.08);
  --transition: 0.25s ease;
  --transition-fast: 0.15s ease;
}

/* Dark theme */
[data-theme='dark'] {
  --color-bg: #0c0a09;
  --color-bg-card: #1c1917;
  --color-bg-code: #292524;
  --color-bg-hover: #292524;
  --color-text: #e7e5e4;
  --color-text-secondary: #a8a29e;
  --color-text-muted: #78716c;
  --color-border: #292524;
  --color-border-light: #1c1917;
  --color-accent: #60a5fa;
  --color-accent-hover: #93c5fd;
  --color-accent-bg: #1e293b;
  --color-tag-bg: #292524;
  --color-tag-text: #a8a29e;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.2);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.4);
}

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
}

body {
  font-family: var(--font-sans);
  font-size: 1rem;
  line-height: 1.7;
  color: var(--color-text);
  background: var(--color-bg);
  transition: background var(--transition), color var(--transition);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

a {
  color: var(--color-accent);
  text-decoration: none;
  transition: color var(--transition-fast);
}

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

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

::selection {
  background: var(--color-accent);
  color: #fff;
}

/* --------------------------------------------------------------------------
   3. Typography
   -------------------------------------------------------------------------- */
h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-sans);
  font-weight: 600;
  line-height: 1.3;
  color: var(--color-text);
  margin-top: var(--space-8);
  margin-bottom: var(--space-4);
}

h1 { font-size: 2rem; }
h2 { font-size: 1.5rem; border-bottom: 1px solid var(--color-border); padding-bottom: var(--space-3); }
h3 { font-size: 1.25rem; }
h4 { font-size: 1.1rem; }

p {
  margin-bottom: var(--space-4);
}

strong {
  font-weight: 600;
}

blockquote {
  margin: var(--space-6) 0;
  padding: var(--space-4) var(--space-6);
  border-left: 3px solid var(--color-accent);
  color: var(--color-text-secondary);
  background: var(--color-accent-bg);
  border-radius: 0 var(--radius) var(--radius) 0;
}

code {
  font-family: var(--font-mono);
  font-size: 0.875em;
  padding: 0.15em 0.4em;
  background: var(--color-bg-code);
  border-radius: var(--radius-sm);
  word-break: break-word;
}

pre {
  margin: var(--space-6) 0;
  padding: var(--space-5);
  background: var(--color-bg-code);
  border-radius: var(--radius);
  overflow-x: auto;
  font-size: 0.875rem;
  line-height: 1.6;
  border: 1px solid var(--color-border);
}

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

ul, ol {
  margin: var(--space-4) 0;
  padding-left: var(--space-6);
}

li {
  margin-bottom: var(--space-2);
}

hr {
  border: none;
  border-top: 1px solid var(--color-border);
  margin: var(--space-10) 0;
}

/* --------------------------------------------------------------------------
   4. Layout — Header
   -------------------------------------------------------------------------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--header-height);
  background: var(--color-bg);
  border-bottom: 1px solid var(--color-border);
  backdrop-filter: blur(12px);
  background: rgba(250, 250, 249, 0.85);
  transition: background var(--transition), border-color var(--transition);
}

[data-theme='dark'] .site-header {
  background: rgba(12, 10, 9, 0.85);
}

.header-inner {
  max-width: 1040px;
  margin: 0 auto;
  padding: 0 var(--space-6);
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.site-title {
  font-size: 1.125rem;
  font-weight: 700;
  color: var(--color-text);
  letter-spacing: -0.02em;
}

.site-title a {
  color: inherit;
}

.site-title a:hover {
  text-decoration: none;
  opacity: 0.8;
}

.site-title .accent {
  color: var(--color-accent);
}

.main-nav {
  display: flex;
  align-items: center;
  gap: var(--space-1);
}

.main-nav a {
  display: inline-flex;
  align-items: center;
  padding: var(--space-2) var(--space-3);
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  border-radius: var(--radius);
  transition: color var(--transition-fast), background var(--transition-fast);
}

.main-nav a:hover,
.main-nav a.active {
  color: var(--color-text);
  background: var(--color-bg-hover);
  text-decoration: none;
}

.main-nav a.active {
  color: var(--color-accent);
  font-weight: 500;
}

/* Theme toggle */
.theme-toggle {
  background: none;
  border: none;
  cursor: pointer;
  padding: var(--space-2);
  border-radius: var(--radius);
  color: var(--color-text-secondary);
  display: flex;
  align-items: center;
  justify-content: center;
  transition: color var(--transition-fast), background var(--transition-fast);
  font-size: 1.1rem;
  line-height: 1;
}

.theme-toggle:hover {
  color: var(--color-text);
  background: var(--color-bg-hover);
}

.theme-toggle .icon-sun,
.theme-toggle .icon-moon {
  display: none;
}

[data-theme='dark'] .theme-toggle .icon-moon {
  display: block;
}

[data-theme='light'] .theme-toggle .icon-sun,
:root:not([data-theme]) .theme-toggle .icon-sun {
  display: block;
}

/* Mobile nav toggle */
.nav-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: var(--space-2);
  color: var(--color-text);
  font-size: 1.25rem;
}

/* --------------------------------------------------------------------------
   5. Layout — Main Content
   -------------------------------------------------------------------------- */
.main-content {
  flex: 1;
  width: 100%;
  max-width: 1040px;
  margin: 0 auto;
  padding: var(--space-12) var(--space-6) var(--space-20);
}

.page-wrapper {
  display: grid;
  grid-template-columns: 1fr var(--sidebar-width);
  gap: var(--space-12);
  align-items: start;
}

.page-wrapper.single-column {
  grid-template-columns: minmax(0, var(--content-max-width));
  justify-content: center;
}

/* --------------------------------------------------------------------------
   6. Sidebar
   -------------------------------------------------------------------------- */
.sidebar {
  position: sticky;
  top: calc(var(--header-height) + var(--space-8));
}

.sidebar-section {
  margin-bottom: var(--space-8);
}

.sidebar-section h3 {
  font-size: 0.8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-text-muted);
  margin: 0 0 var(--space-4) 0;
  border: none;
  padding: 0;
}

.sidebar-about {
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  line-height: 1.6;
}

.sidebar-tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
}

.tag {
  display: inline-flex;
  align-items: center;
  font-size: 0.8rem;
  padding: 0.2em 0.7em;
  background: var(--color-tag-bg);
  color: var(--color-tag-text);
  border-radius: 20px;
  transition: all var(--transition-fast);
}

.tag:hover {
  background: var(--color-accent);
  color: #fff;
  text-decoration: none;
}

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

.sidebar-links li {
  margin-bottom: var(--space-2);
}

.sidebar-links a {
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  display: flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-1) 0;
}

.sidebar-links a:hover {
  color: var(--color-accent);
  text-decoration: none;
}

/* --------------------------------------------------------------------------
   7. Home Page — Post List
   -------------------------------------------------------------------------- */
.post-list {
  list-style: none;
  padding: 0;
  margin: 0;
}

.post-item {
  padding: var(--space-6) 0;
  border-bottom: 1px solid var(--color-border-light);
  transition: opacity var(--transition);
}

.post-item:first-child {
  padding-top: 0;
}

.post-item:last-child {
  border-bottom: none;
}

.post-meta {
  font-size: 0.85rem;
  color: var(--color-text-muted);
  margin-bottom: var(--space-2);
  display: flex;
  align-items: center;
  gap: var(--space-3);
  flex-wrap: wrap;
}

.post-meta .date {
  font-feature-settings: 'tnum';
}

.post-meta .dot {
  color: var(--color-border);
}

.post-title {
  font-size: 1.35rem;
  font-weight: 600;
  margin: 0 0 var(--space-2) 0;
  line-height: 1.35;
}

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

.post-title a:hover {
  color: var(--color-accent);
  text-decoration: none;
}

.post-excerpt {
  font-size: 0.95rem;
  color: var(--color-text-secondary);
  line-height: 1.7;
  margin-bottom: var(--space-3);
}

.post-tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin-top: var(--space-3);
}

.post-item .tag {
  font-size: 0.75rem;
}

/* --------------------------------------------------------------------------
   8. Archive Page
   -------------------------------------------------------------------------- */
.archive-header {
  margin-bottom: var(--space-10);
}

.archive-header h1 {
  margin-top: 0;
}

.archive-year {
  margin-bottom: var(--space-8);
}

.archive-year-title {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--color-text);
  margin-bottom: var(--space-4);
  padding-bottom: var(--space-2);
  border-bottom: 2px solid var(--color-accent);
  display: inline-block;
}

.archive-month {
  margin-bottom: var(--space-6);
}

.archive-month-title {
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--color-text-secondary);
  margin-bottom: var(--space-3);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.archive-list {
  list-style: none;
  padding: 0;
  margin: 0;
}

.archive-list li {
  display: flex;
  align-items: baseline;
  gap: var(--space-4);
  padding: var(--space-2) 0;
  border-bottom: 1px dashed var(--color-border-light);
  margin: 0;
}

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

.archive-list .date {
  font-size: 0.85rem;
  color: var(--color-text-muted);
  font-feature-settings: 'tnum';
  min-width: 3.2em;
  flex-shrink: 0;
}

.archive-list a {
  font-size: 0.95rem;
  color: var(--color-text);
  flex: 1;
}

.archive-list a:hover {
  color: var(--color-accent);
  text-decoration: none;
}

.archive-count {
  font-size: 0.9rem;
  color: var(--color-text-muted);
  margin-bottom: var(--space-8);
}

/* Archive filter */
.archive-filter {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin-bottom: var(--space-8);
  padding-bottom: var(--space-6);
  border-bottom: 1px solid var(--color-border);
}

.filter-btn {
  font-size: 0.85rem;
  padding: var(--space-1) var(--space-3);
  border: 1px solid var(--color-border);
  border-radius: 20px;
  background: transparent;
  color: var(--color-text-secondary);
  cursor: pointer;
  transition: all var(--transition-fast);
}

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

/* --------------------------------------------------------------------------
   9. Article / Post Page
   -------------------------------------------------------------------------- */
.article {
  max-width: var(--content-max-width);
  margin: 0 auto;
}

.article-header {
  margin-bottom: var(--space-10);
}

.article-header .post-meta {
  font-size: 0.9rem;
  margin-bottom: var(--space-3);
}

.article-header h1 {
  font-size: 2rem;
  font-weight: 700;
  margin: 0 0 var(--space-4) 0;
  line-height: 1.3;
  border: none;
  padding: 0;
}

.article-body {
  font-family: var(--font-body);
  font-size: 1.1rem;
  line-height: 1.9;
  color: var(--color-text);
}

.article-body h2 {
  font-family: var(--font-sans);
  margin-top: var(--space-12);
}

.article-body h3 {
  font-family: var(--font-sans);
  margin-top: var(--space-10);
}

/* --------------------------------------------------------------------------
   Table of Contents
   -------------------------------------------------------------------------- */
.toc-wrapper {
  margin: var(--space-6) 0 var(--space-10);
}

.toc {
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  background: var(--color-bg-card);
  padding: var(--space-3) var(--space-5);
}

.toc[open] {
  padding-bottom: var(--space-4);
}

.toc-title {
  font-family: var(--font-sans);
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-accent);
  cursor: pointer;
  user-select: none;
  padding: var(--space-1) 0;
}

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

.toc-body {
  margin-top: var(--space-3);
  font-size: 0.9rem;
  line-height: 1.8;
}

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

.toc-body nav ul li {
  margin: 0;
  padding: 0;
}

.toc-body nav ul li a {
  display: block;
  padding: var(--space-1) var(--space-2);
  color: var(--color-text-secondary);
  border-left: 2px solid transparent;
  transition: all var(--transition-fast);
  text-decoration: none;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}

.toc-body nav ul li a:hover {
  color: var(--color-accent);
  border-left-color: var(--color-accent);
  background: var(--color-accent-bg);
  text-decoration: none;
}

.toc-body nav ul li a.active {
  color: var(--color-accent);
  border-left-color: var(--color-accent);
  font-weight: 500;
}

/* Second-level indentation */
.toc-body nav ul ul {
  padding-left: var(--space-4);
  font-size: 0.85rem;
}

/* --------------------------------------------------------------------------
   Article body
   -------------------------------------------------------------------------- */

.article-body a {
  text-decoration: underline;
  text-underline-offset: 3px;
  text-decoration-thickness: 1px;
}

.article-body a:hover {
  text-decoration-thickness: 2px;
}

.article-body ul,
.article-body ol {
  margin: var(--space-4) 0;
  padding-left: var(--space-6);
}

.article-body li {
  margin-bottom: var(--space-2);
}

.article-body img {
  margin: var(--space-8) auto;
  border-radius: var(--radius);
  box-shadow: var(--shadow-md);
}

.article-body table {
  width: 100%;
  border-collapse: collapse;
  margin: var(--space-6) 0;
  font-size: 0.9rem;
  font-family: var(--font-sans);
}

.article-body th,
.article-body td {
  padding: var(--space-3) var(--space-4);
  border: 1px solid var(--color-border);
  text-align: left;
}

.article-body th {
  background: var(--color-bg-code);
  font-weight: 600;
}

/* Reading progress bar */
.reading-progress {
  position: fixed;
  top: var(--header-height);
  left: 0;
  width: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--color-accent), #8b5cf6);
  z-index: 99;
  transition: width 0.1s linear;
}

/* Article navigation (prev/next) */
.article-nav {
  display: flex;
  justify-content: space-between;
  gap: var(--space-6);
  margin-top: var(--space-16);
  padding-top: var(--space-8);
  border-top: 1px solid var(--color-border);
}

.article-nav a {
  flex: 1;
  max-width: 50%;
  padding: var(--space-4);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  transition: all var(--transition-fast);
}

.article-nav a:hover {
  border-color: var(--color-accent);
  background: var(--color-accent-bg);
  text-decoration: none;
}

.article-nav .nav-label {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: var(--space-1);
}

.article-nav .nav-title {
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--color-text);
}

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

/* --------------------------------------------------------------------------
   10. About Page
   -------------------------------------------------------------------------- */
.about-content {
  max-width: var(--content-max-width);
  margin: 0 auto;
}

.about-header {
  text-align: center;
  margin-bottom: var(--space-12);
}

.about-avatar {
  width: 96px;
  height: 96px;
  border-radius: 50%;
  background: var(--color-accent-bg);
  margin: 0 auto var(--space-6);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 2.5rem;
  color: var(--color-accent);
  border: 3px solid var(--color-border);
}

.about-header h1 {
  margin: 0 0 var(--space-2) 0;
  border: none;
}

.about-header .subtitle {
  color: var(--color-text-secondary);
  font-size: 1rem;
}

.about-section {
  margin-bottom: var(--space-10);
}

.about-section h2 {
  border: none;
  margin-top: 0;
  margin-bottom: var(--space-4);
}

.skill-list {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
  margin: var(--space-4) 0;
}

.skill-item {
  padding: var(--space-2) var(--space-4);
  background: var(--color-bg-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  font-size: 0.9rem;
  transition: all var(--transition-fast);
}

.skill-item:hover {
  border-color: var(--color-accent);
  background: var(--color-accent-bg);
}

/* Social links */
.social-links {
  display: flex;
  gap: var(--space-4);
  justify-content: center;
  margin-top: var(--space-6);
}

.social-links a {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-4);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  font-size: 0.9rem;
  color: var(--color-text-secondary);
  transition: all var(--transition-fast);
}

.social-links a:hover {
  color: var(--color-accent);
  border-color: var(--color-accent);
  text-decoration: none;
}

/* --------------------------------------------------------------------------
   11. Footer
   -------------------------------------------------------------------------- */
.site-footer {
  border-top: 1px solid var(--color-border);
  padding: var(--space-8) var(--space-6);
  text-align: center;
  font-size: 0.85rem;
  color: var(--color-text-muted);
}

.site-footer a {
  color: var(--color-text-secondary);
}

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

/* --------------------------------------------------------------------------
   12. Search Bar
   -------------------------------------------------------------------------- */
.search-box {
  position: relative;
  margin-bottom: var(--space-6);
}

.search-box input {
  width: 100%;
  padding: var(--space-3) var(--space-4) var(--space-3) var(--space-10);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  background: var(--color-bg-card);
  color: var(--color-text);
  font-size: 0.9rem;
  font-family: var(--font-sans);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
  outline: none;
}

.search-box input:focus {
  border-color: var(--color-accent);
  box-shadow: 0 0 0 3px var(--color-accent-bg);
}

.search-box .search-icon {
  position: absolute;
  left: var(--space-3);
  top: 50%;
  transform: translateY(-50%);
  color: var(--color-text-muted);
  pointer-events: none;
  font-size: 1rem;
}

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

/* Search results count */
.search-info {
  font-size: 0.85rem;
  color: var(--color-text-muted);
  margin-bottom: var(--space-4);
}

/* --------------------------------------------------------------------------
   13. Pagination
   -------------------------------------------------------------------------- */
.pagination {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-4);
  margin-top: var(--space-8);
  padding-top: var(--space-6);
  border-top: 1px solid var(--color-border-light);
}

.pagination a {
  font-size: 0.9rem;
  padding: var(--space-2) var(--space-4);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  color: var(--color-text-secondary);
  transition: all var(--transition-fast);
}

.pagination a:hover {
  border-color: var(--color-accent);
  color: var(--color-accent);
  background: var(--color-accent-bg);
  text-decoration: none;
}

.pagination-info {
  font-size: 0.85rem;
  color: var(--color-text-muted);
}

/* --------------------------------------------------------------------------
   14. Animations — Scroll Reveal
   -------------------------------------------------------------------------- */
.reveal {
  opacity: 0;
  transform: translateY(20px);
  transition: opacity 0.5s ease, transform 0.5s ease;
}

.reveal.visible {
  opacity: 1;
  transform: translateY(0);
}

/* Staggered delay helpers */
.reveal-delay-1 { transition-delay: 0.05s; }
.reveal-delay-2 { transition-delay: 0.1s; }
.reveal-delay-3 { transition-delay: 0.15s; }
.reveal-delay-4 { transition-delay: 0.2s; }

/* --------------------------------------------------------------------------
   15. Page Header
   -------------------------------------------------------------------------- */
.page-header {
  margin-bottom: var(--space-10);
}

.page-header h1 {
  margin-top: 0;
  font-size: 2rem;
}

.page-header p {
  color: var(--color-text-secondary);
  font-size: 1rem;
  margin-top: var(--space-2);
}

/* --------------------------------------------------------------------------
   16. 404 Page
   -------------------------------------------------------------------------- */
.error-page {
  text-align: center;
  padding: var(--space-20) 0;
}

.error-page h1 {
  font-size: 4rem;
  color: var(--color-text-muted);
  margin: 0;
  border: none;
}

.error-page p {
  color: var(--color-text-secondary);
  margin: var(--space-4) 0 var(--space-8);
}

/* --------------------------------------------------------------------------
   16. Back to Top
   -------------------------------------------------------------------------- */
.back-to-top {
  position: fixed;
  bottom: var(--space-8);
  right: var(--space-8);
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: var(--color-bg-card);
  border: 1px solid var(--color-border);
  color: var(--color-text-secondary);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.2rem;
  opacity: 0;
  visibility: hidden;
  transition: all var(--transition);
  box-shadow: var(--shadow-md);
  z-index: 50;
}

.back-to-top.visible {
  opacity: 1;
  visibility: visible;
}

.back-to-top:hover {
  background: var(--color-accent);
  color: #fff;
  border-color: var(--color-accent);
}

/* --------------------------------------------------------------------------
   17. Responsive — Tablet
   -------------------------------------------------------------------------- */
@media (max-width: 820px) {
  .page-wrapper {
    grid-template-columns: 1fr;
    gap: var(--space-8);
  }

  .sidebar {
    position: static;
    order: -1;
  }

  .sidebar-section h3 {
    font-size: 0.75rem;
  }

  .article-header h1 {
    font-size: 1.7rem;
  }

  .article-body {
    font-size: 1.05rem;
  }

  .error-page h1 {
    font-size: 3rem;
  }
}

/* --------------------------------------------------------------------------
   18. Responsive — Mobile
   -------------------------------------------------------------------------- */
@media (max-width: 640px) {
  :root {
    --header-height: 52px;
  }

  .header-inner {
    padding: 0 var(--space-4);
  }

  .nav-toggle {
    display: flex;
    align-items: center;
    justify-content: center;
  }

  .main-nav {
    display: none;
    position: absolute;
    top: var(--header-height);
    left: 0;
    right: 0;
    background: var(--color-bg-card);
    border-bottom: 1px solid var(--color-border);
    flex-direction: column;
    padding: var(--space-3);
    gap: var(--space-1);
    box-shadow: var(--shadow-md);
  }

  .main-nav.open {
    display: flex;
  }

  .main-nav a {
    width: 100%;
    padding: var(--space-3) var(--space-4);
  }

  .main-content {
    padding: var(--space-8) var(--space-4) var(--space-16);
  }

  .post-title {
    font-size: 1.15rem;
  }

  .post-excerpt {
    font-size: 0.9rem;
  }

  .post-meta {
    font-size: 0.8rem;
  }

  .archive-list li {
    flex-direction: column;
    gap: var(--space-1);
    padding: var(--space-3) 0;
  }

  .archive-list .date {
    min-width: auto;
  }

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

  .article-body {
    font-size: 1rem;
    line-height: 1.85;
  }

  blockquote {
    padding: var(--space-3) var(--space-4);
    margin: var(--space-4) 0;
  }

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

  .article-nav a {
    max-width: 100%;
  }

  .article-nav .nav-next {
    text-align: left;
  }

  .social-links {
    flex-wrap: wrap;
  }

  .about-avatar {
    width: 72px;
    height: 72px;
    font-size: 2rem;
  }

  .back-to-top {
    bottom: var(--space-4);
    right: var(--space-4);
    width: 36px;
    height: 36px;
    font-size: 1rem;
  }

  .reading-progress {
    top: var(--header-height);
  }
}

/* --------------------------------------------------------------------------
   19. Print
   -------------------------------------------------------------------------- */
@media print {
  .site-header,
  .sidebar,
  .back-to-top,
  .reading-progress,
  .article-nav {
    display: none;
  }

  body {
    background: #fff;
    color: #000;
  }

  .main-content {
    padding: 0;
    max-width: 100%;
  }

  a {
    color: inherit;
  }
}

/* --------------------------------------------------------------------------
   20. 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-width: 0;
}

.fade-in {
  animation: fadeIn 0.5s ease forwards;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(10px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* Smooth scrollbar for code blocks */
pre::-webkit-scrollbar {
  height: 6px;
}

pre::-webkit-scrollbar-track {
  background: transparent;
}

pre::-webkit-scrollbar-thumb {
  background: var(--color-border);
  border-radius: 3px;
}