/* ============================================================
   DESIGN TOKENS
   ============================================================ */
:root {
  --color-bg:           #f6f8fa;
  --color-surface:      #ffffff;
  --color-border:       #e5e7eb;
  --color-border-strong:#d1d5db;

  --color-text:         #1f2328;
  --color-text-muted:   #59636e;
  --color-text-subtle:  #8b949e;

  --color-accent:       #1d4ed8;
  --color-accent-hover: #1e40af;
  --color-accent-bg:    #eff6ff;
  --color-accent-text:  #1e40af;

  --color-code-bg:      #0f1621;
  --color-code-fg:      #d4cfc8;
  --color-code-border:  #1e2d3d;

  --font-sans:   -apple-system, BlinkMacSystemFont, "Segoe UI", "Helvetica Neue", Arial, sans-serif;
  --font-ui:     var(--font-sans);
  --font-mono:   ui-monospace, "Cascadia Code", "Fira Code", Menlo, Consolas, monospace;

  --text-base:   1rem;
  --text-sm:     0.875rem;
  --text-xs:     0.8rem;

  --leading-body:    1.7;
  --leading-heading: 1.2;

  --space-1:  4px;
  --space-2:  8px;
  --space-3:  12px;
  --space-4:  16px;
  --space-5:  20px;
  --space-6:  24px;
  --space-8:  32px;
  --space-10: 40px;
  --space-12: 48px;

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;

  --shadow-card: 0 1px 3px rgba(26, 25, 23, 0.06),
                 0 8px 24px rgba(26, 25, 23, 0.07),
                 0 0 0 1px rgba(26, 25, 23, 0.04);

  --transition: 150ms ease;

  --sidebar-width:           260px;
  --topbar-height:           56px;
  --toc-rail-width:          220px;
  --content-max:             820px;
  --sidebar-bg:              #fafbfc;
  --sidebar-item-hover:      #eef1f4;
  --sidebar-item-active-bg:  var(--color-accent-bg);
  --sidebar-item-active-text:var(--color-accent-text);
}

/* ============================================================
   RESET & BASE
   ============================================================ */
*, *::before, *::after {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: var(--text-base);
  background: var(--color-surface);
  color: var(--color-text);
  line-height: var(--leading-body);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
}

/* ============================================================
   TOPBAR
   ============================================================ */
.topbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  height: var(--topbar-height);
  display: flex;
  align-items: center;
  padding: 0 var(--space-5);
  gap: var(--space-3);
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
}

.topbar-logo {
  font-family: var(--font-ui);
  font-size: 0.95rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--color-text);
  text-decoration: none;
}

.topbar-logo:hover {
  color: var(--color-text);
  text-decoration: none;
}

/* Hamburger — visible only on mobile */
.topbar-menu-btn {
  display: none;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  background: none;
  border: none;
  border-radius: var(--radius-sm);
  cursor: pointer;
  color: var(--color-text-muted);
  transition: background var(--transition);
  flex-shrink: 0;
}

.topbar-menu-btn:hover {
  background: var(--sidebar-item-hover);
  color: var(--color-text);
}

/* ============================================================
   PAGE SHELL
   ============================================================ */
.page-layout {
  display: flex;
  min-height: 100vh;
  padding-top: var(--topbar-height);
}

/* ============================================================
   SIDEBAR
   ============================================================ */
.sidebar {
  position: fixed;
  top: var(--topbar-height);
  left: 0;
  bottom: 0;
  width: var(--sidebar-width);
  background: var(--sidebar-bg);
  border-right: 1px solid var(--color-border);
  overflow-y: auto;
  padding: var(--space-5) 0 var(--space-10);
  scrollbar-width: thin;
  scrollbar-color: var(--color-border) transparent;
  z-index: 80;
}

.sidebar::-webkit-scrollbar { width: 4px; }
.sidebar::-webkit-scrollbar-thumb {
  background: var(--color-border);
  border-radius: 2px;
}

.sidebar-section {
  margin: var(--space-5) 0 var(--space-1);
}

.sidebar-section-label {
  display: block;
  font-family: var(--font-ui);
  font-size: 0.7rem;
  font-weight: 600;
  letter-spacing: 0.07em;
  text-transform: uppercase;
  color: var(--color-text-muted);
  padding: 0 var(--space-4) var(--space-1);
}

.sidebar-nav {
  list-style: none;
  margin: 0;
  padding: 0 var(--space-3);
}

.sidebar-nav li {
  margin-bottom: 1px;
}

.sidebar-nav a {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius-sm);
  font-family: var(--font-ui);
  font-size: var(--text-sm);
  font-weight: 450;
  color: var(--color-text-muted);
  text-decoration: none;
  transition: background var(--transition), color var(--transition);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.sidebar-nav a:hover {
  background: var(--sidebar-item-hover);
  color: var(--color-text);
  text-decoration: none;
}

.sidebar-nav a.active {
  background: var(--sidebar-item-active-bg);
  color: var(--sidebar-item-active-text);
  font-weight: 550;
}

/* Sub-items */
.sidebar-nav .subnav {
  list-style: none;
  padding: var(--space-1) 0 var(--space-1) var(--space-5);
  margin: 0;
}

.sidebar-nav .subnav li { margin-bottom: 0; }

.sidebar-nav .subnav a {
  font-size: 0.82rem;
  padding: 4px var(--space-3);
  color: var(--color-text-muted);
}

.sidebar-nav .subnav a:hover { color: var(--color-text); }

.sidebar-nav .subnav a.active {
  color: var(--sidebar-item-active-text);
  background: var(--sidebar-item-active-bg);
  font-weight: 550;
}

.sidebar-nav .nav-group {
  display: block;
  padding: var(--space-2) var(--space-3) 0;
  font-family: var(--font-ui);
  font-size: var(--text-sm);
  font-weight: 450;
  color: var(--color-text-muted);
}

/* ============================================================
   MAIN CONTENT
   ============================================================ */
.main-content {
  flex: 1;
  margin-left: var(--sidebar-width);
  min-width: 0;
}

.container {
  max-width: var(--content-max);
  margin: 0 auto;
  padding: var(--space-10) var(--space-12) var(--space-12);
}

/* ============================================================
   MOBILE
   ============================================================ */
@media (max-width: 860px) {
  .topbar-menu-btn { display: flex; }

  .sidebar {
    transform: translateX(-100%);
    transition: transform 200ms ease, box-shadow 200ms ease;
    z-index: 90;
  }

  .sidebar.open {
    transform: translateX(0);
    box-shadow: 4px 0 24px rgba(26, 25, 23, 0.1);
  }

  .main-content { margin-left: 0; }

  .container {
    padding: var(--space-8) var(--space-6) var(--space-10);
  }

  .sidebar-overlay {
    display: none;
    position: fixed;
    inset: var(--topbar-height) 0 0 0;
    background: rgba(26, 25, 23, 0.3);
    z-index: 89;
    backdrop-filter: blur(2px);
  }

  .sidebar-overlay.open { display: block; }
}

@media (max-width: 480px) {
  .container {
    padding: var(--space-6) var(--space-4) var(--space-8);
  }
}

/* ============================================================
   TYPOGRAPHY
   ============================================================ */
h1, h2, h3, h4 {
  font-family: var(--font-ui);
  line-height: var(--leading-heading);
  font-weight: 600;
  letter-spacing: -0.025em;
  color: var(--color-text);
}

h1 {
  font-size: clamp(1.75rem, 4vw, 2.4rem);
  margin: 0 0 var(--space-2);
  letter-spacing: -0.035em;
}

h2 {
  font-size: 1.3rem;
  margin: var(--space-12) 0 var(--space-4);
  padding-bottom: var(--space-3);
  border-bottom: 1px solid var(--color-border);
  font-weight: 600;
}

h3 {
  font-size: 1.05rem;
  margin: var(--space-8) 0 var(--space-2);
  color: var(--color-text);
  font-weight: 600;
}

h4 {
  margin: var(--space-6) 0 var(--space-2);
  color: var(--color-text-muted);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  font-size: 0.78rem;
}

p {
  margin: 0 0 var(--space-4);
  max-width: 65ch;
}

/* ============================================================
   LINKS
   ============================================================ */
a {
  color: var(--color-accent);
  text-decoration: underline;
  text-underline-offset: 2px;
  text-decoration-thickness: 1px;
  text-decoration-color: color-mix(in srgb, var(--color-accent) 40%, transparent);
  transition: color var(--transition), text-decoration-color var(--transition);
}

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

/* ============================================================
   LISTS
   ============================================================ */
ul, ol {
  padding-left: var(--space-5);
  margin: 0 0 var(--space-4);
}

li { margin-bottom: var(--space-1); }
li::marker { color: var(--color-text-subtle); }

/* ============================================================
   CODE
   ============================================================ */
code {
  font-family: var(--font-mono);
  font-size: 0.88em;
}

:not(pre) > code {
  background: #f0ede8;
  color: #b45309;
  padding: 1px 5px;
  border-radius: var(--radius-sm);
  border: 1px solid #e5ddd3;
}

.code-block {
  position: relative;
  margin: var(--space-4) 0 var(--space-6);
  border-radius: var(--radius-md);
  overflow: hidden;
  border: 1px solid var(--color-code-border);
  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.2), 0 1px 3px rgba(0, 0, 0, 0.15);
}

.code-block[data-lang]::before {
  content: attr(data-lang);
  display: block;
  background: #1a2540;
  color: #5b7db5;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  font-weight: 500;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  padding: var(--space-2) var(--space-4);
  border-bottom: 1px solid var(--color-code-border);
}

pre {
  margin: 0;
  padding: var(--space-5);
  background: var(--color-code-bg);
  color: var(--color-code-fg);
  overflow-x: auto;
  font-size: var(--text-sm);
  line-height: 1.65;
  tab-size: 2;
}

pre::-webkit-scrollbar { height: 6px; }
pre::-webkit-scrollbar-track { background: transparent; }
pre::-webkit-scrollbar-thumb { background: #2d3f55; border-radius: 3px; }

/* ============================================================
   COPY BUTTON
   ============================================================ */
.copy-btn {
  position: absolute;
  top: var(--space-3);
  right: var(--space-3);
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  font-family: var(--font-ui);
  font-size: 0.72rem;
  font-weight: 500;
  letter-spacing: 0.02em;
  padding: var(--space-1) var(--space-3);
  border-radius: var(--radius-sm);
  border: 1px solid #2d3f55;
  background: rgba(255, 255, 255, 0.06);
  color: #8fa8c8;
  cursor: pointer;
  opacity: 0;
  transition: opacity var(--transition), background var(--transition), color var(--transition);
}

.code-block:hover .copy-btn { opacity: 1; }

.copy-btn:hover {
  background: rgba(255, 255, 255, 0.12);
  color: #c8d8e8;
  border-color: #3d5575;
}

.copy-btn:active { transform: scale(0.96); }

/* ============================================================
   HEADER METADATA & BADGE
   ============================================================ */
.header-meta {
  font-family: var(--font-ui);
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  margin-bottom: var(--space-6);
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-3);
  line-height: 1.4;
}

.badge-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  margin: var(--space-3) 0 var(--space-6);
  padding: var(--space-2) var(--space-4);
  background: var(--color-accent-bg);
  color: var(--color-accent-text);
  border: 1px solid color-mix(in srgb, var(--color-accent) 20%, transparent);
  border-radius: 100px;
  font-family: var(--font-ui);
  font-size: var(--text-sm);
  font-weight: 500;
  text-decoration: none;
  transition: background var(--transition), border-color var(--transition), box-shadow var(--transition);
}

.badge-link:hover {
  background: color-mix(in srgb, var(--color-accent) 10%, white);
  border-color: color-mix(in srgb, var(--color-accent) 35%, transparent);
  box-shadow: 0 2px 8px rgba(29, 78, 216, 0.12);
  text-decoration: none;
}

/* ============================================================
   FOOTER
   ============================================================ */
footer {
  font-family: var(--font-ui);
  font-size: var(--text-sm);
  color: var(--color-text-subtle);
  margin-top: var(--space-12);
  padding-top: var(--space-6);
  border-top: 1px solid var(--color-border);
}

/* ============================================================
   LARGE SCREENS
   ============================================================ */
/* Right-hand "On this page" outline (built by main.js from h2 headings) */
.toc-rail {
  display: none;
}

@media (min-width: 1280px) {
  .main-content { padding-right: calc(var(--toc-rail-width) + var(--space-8)); }
  .toc-rail {
    display: block;
    position: fixed;
    top: calc(var(--topbar-height) + var(--space-10));
    right: var(--space-6);
    width: var(--toc-rail-width);
    max-height: calc(100vh - var(--topbar-height) - var(--space-12));
    overflow-y: auto;
    font-family: var(--font-ui);
    font-size: var(--text-xs);
    border-left: 1px solid var(--color-border);
    padding-left: var(--space-4);
  }
  .toc-rail-title {
    margin: 0 0 var(--space-2);
    font-size: 0.7rem;
    font-weight: 600;
    letter-spacing: 0.07em;
    text-transform: uppercase;
    color: var(--color-text-muted);
  }
  .toc-rail ol {
    list-style: none;
    margin: 0;
    padding: 0;
  }
  .toc-rail li { margin: 0; }
  .toc-rail a {
    display: block;
    padding: 3px 0;
    color: var(--color-text-muted);
    text-decoration: none;
    line-height: 1.4;
  }
  .toc-rail a:hover { color: var(--color-text); }
  .toc-rail a.active {
    color: var(--color-accent);
    font-weight: 600;
  }
  /* The rail replaces the inline "On this page" box on wide screens */
  .container .toc { display: none; }
}

/* ============================================================
   USABILITY AND ACCESSIBILITY
   ============================================================ */
html { scroll-behavior: smooth; }
h2[id], h3[id] { scroll-margin-top: calc(var(--topbar-height) + var(--space-4)); }

/* Visible keyboard focus */
a:focus-visible,
button:focus-visible,
summary:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 2px;
  border-radius: var(--radius-sm);
}

/* Copy button: always visible on touch screens and when focused */
.code-block:focus-within .copy-btn { opacity: 1; }
@media (hover: none) {
  .copy-btn { opacity: 1; }
}

/* Subtitle under the page title */
.page-subtitle {
  font-family: var(--font-ui);
  font-size: 1.1rem;
  color: var(--color-text-muted);
  margin: var(--space-2) 0 var(--space-6);
  max-width: none;
}

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

.embed-frame {
  display: block;
  width: 100%;
  height: 600px;
  margin-top: var(--space-4);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
}

/* Note boxes */
.callout {
  background: var(--color-accent-bg);
  border-left: 4px solid var(--color-accent);
  padding: var(--space-4);
  margin: var(--space-6) 0;
  border-radius: var(--radius-sm);
}
.callout > :last-child { margin-bottom: 0; }

/* "On this page" list */
.toc {
  font-family: var(--font-ui);
  font-size: var(--text-sm);
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-3) var(--space-4);
  margin: 0 0 var(--space-8);
}
.toc summary {
  cursor: pointer;
  font-weight: 600;
  color: var(--color-text);
}
.toc ol { margin: var(--space-2) 0 0; padding-left: var(--space-5); }
.toc li { margin-bottom: 2px; }
.toc a { text-decoration: none; }
.toc a:hover { text-decoration: underline; }

/* Previous / next links at the end of a page */
.page-nav {
  display: flex;
  justify-content: space-between;
  gap: var(--space-4);
  margin-top: var(--space-12);
  padding-top: var(--space-6);
  border-top: 1px solid var(--color-border);
  font-family: var(--font-ui);
  font-size: var(--text-sm);
}
.page-nav a {
  display: flex;
  flex-direction: column;
  gap: 2px;
  padding: var(--space-3) var(--space-4);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  text-decoration: none;
  max-width: 48%;
}
.page-nav a:hover { border-color: var(--color-accent); }
.page-nav .page-nav-next { margin-left: auto; text-align: right; }
.page-nav span { color: var(--color-text-muted); font-size: var(--text-xs); }

/* Back to top */
.back-to-top {
  position: fixed;
  right: var(--space-5);
  bottom: var(--space-5);
  z-index: 70;
  font-family: var(--font-ui);
  font-size: var(--text-sm);
  padding: var(--space-2) var(--space-4);
  border-radius: 100px;
  border: 1px solid var(--color-border-strong);
  background: var(--color-surface);
  color: var(--color-text);
  box-shadow: var(--shadow-card);
  cursor: pointer;
  opacity: 0;
  pointer-events: none;
  transition: opacity var(--transition);
}
.back-to-top.visible { opacity: 1; pointer-events: auto; }

/* ============================================================
   DARK MODE (light by default, dark by manual choice)
   ============================================================ */
/* Manual dark mode via data-theme attribute */
:root[data-theme="dark"] {
  --color-bg:            #16181c;
  --color-surface:       #1e2126;
  --color-border:        #2e333a;
  --color-border-strong: #4a5059;
  --color-text:          #e7e4df;
  --color-text-muted:    #a8a29b;
  --color-text-subtle:   #8a847d;
  --color-accent:        #7aa2ff;
  --color-accent-hover:  #a3bfff;
  --color-accent-bg:     #1c2740;
  --color-accent-text:   #a3bfff;
  --sidebar-bg:          #1a1d21;
  --sidebar-item-hover:  #262a30;
  --shadow-card: 0 0 0 1px rgba(255, 255, 255, 0.04);
}
:root[data-theme="dark"] :not(pre) > code {
  background: #2a2e35;
  color: #f0b36a;
  border-color: #3a3f47;
}
:root[data-theme="dark"] .badge-link:hover { background: #22304f; }
:root[data-theme="dark"] .sidebar-overlay { background: rgba(0, 0, 0, 0.5); }

/* ============================================================
   THEME TOGGLE BUTTON
   ============================================================ */
.theme-toggle {
  margin-left: auto;
  flex-shrink: 0;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  padding: 0;
  border-radius: 50%;
  border: 1px solid var(--color-border-strong);
  background: var(--color-surface);
  color: var(--color-text);
  cursor: pointer;
  transition: background var(--transition);
}

.theme-toggle:hover {
  background: var(--sidebar-item-hover);
}

.theme-toggle svg { width: 18px; height: 18px; display: block; }

/* Moon (switch to dark) in light mode, sun (switch to light) in dark mode.
   Chosen in CSS so the right icon shows before the script runs. */
.theme-toggle .icon-sun { display: none; }
:root[data-theme="dark"] .theme-toggle .icon-sun { display: block; }
:root[data-theme="dark"] .theme-toggle .icon-moon { display: none; }

/* ============================================================
   PRINT
   ============================================================ */
@media print {
  .topbar, .sidebar, .sidebar-overlay, .copy-btn, .back-to-top, .page-nav, .toc, .theme-toggle { display: none !important; }
  .page-layout { padding-top: 0; }
  .main-content { margin-left: 0; }
  .container { box-shadow: none; border: none; margin: 0; padding: 0; max-width: none; }
  body { background: #fff; color: #000; }
  pre { background: #f5f5f5; color: #000; border: 1px solid #ccc; white-space: pre-wrap; word-break: break-all; }
  .code-block { box-shadow: none; border: none; }
  a { color: #000; }
  h2, h3 { break-after: avoid; }
  pre, .callout { break-inside: avoid; }
}