/* ==========================================================================
   layout.css
   Page skeleton: header, sidebar, content, on-page TOC, footer + responsive.
   ========================================================================== */

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-h) + var(--sp-4));
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-sans);
  font-size: var(--fs-base);
  line-height: var(--lh-base);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

/* Accessibility: skip link */
.skip-link {
  position: absolute;
  inset-inline-start: var(--sp-4);
  top: -60px;
  z-index: 200;
  background: var(--accent);
  color: #fff;
  padding: var(--sp-2) var(--sp-4);
  border-radius: var(--radius-sm);
  transition: top 0.2s ease;
}
.skip-link:focus {
  top: var(--sp-2);
}

/* -------- Header -------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--header-h);
  display: flex;
  align-items: center;
  gap: var(--sp-4);
  padding: 0 var(--sp-5);
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: saturate(1.4) blur(8px);
  border-bottom: 1px solid var(--border);
}

.site-header__brand {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
  font-weight: 700;
  color: var(--text);
  text-decoration: none;
  white-space: nowrap;
}
.site-header__brand .logo {
  width: 30px;
  height: 30px;
  flex: none;
}
.site-header__brand small {
  display: block;
  font-weight: 500;
  font-size: var(--fs-xs);
  color: var(--text-muted);
}

.site-header__spacer {
  flex: 1;
}

.header-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--sp-2);
  height: 38px;
  min-width: 38px;
  padding: 0 var(--sp-3);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--bg-elevated);
  color: var(--text-muted);
  text-decoration: none;
  cursor: pointer;
  font: inherit;
  font-size: var(--fs-sm);
  transition: color 0.15s, border-color 0.15s, background 0.15s;
}
.header-btn:hover {
  color: var(--accent);
  border-color: var(--accent);
}

/* Hamburger only on small screens */
.menu-toggle {
  display: none;
}

/* -------- Layout grid -------- */
.layout {
  display: grid;
  grid-template-columns: var(--sidebar-w) minmax(0, 1fr) var(--toc-w);
  align-items: start;
  max-width: 1400px;
  margin: 0 auto;
}

/* -------- Sidebar (chapter list) -------- */
.sidebar {
  position: sticky;
  top: var(--header-h);
  align-self: start;
  height: calc(100vh - var(--header-h));
  overflow-y: auto;
  padding: var(--sp-5) var(--sp-4);
  border-inline-end: 1px solid var(--border);
  background: var(--bg);
}
.sidebar__title {
  font-size: var(--fs-xs);
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--text-faint);
  margin: 0 var(--sp-2) var(--sp-3);
}
.sidebar__nav {
  list-style: none;
  margin: 0;
  padding: 0;
  counter-reset: chap;
}
.sidebar__nav a {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
  padding: var(--sp-2) var(--sp-3);
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  text-decoration: none;
  font-size: var(--fs-sm);
  line-height: 1.5;
  transition: background 0.15s, color 0.15s;
}
.sidebar__nav a .num {
  flex: none;
  width: 26px;
  height: 26px;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--bg-subtle);
  border: 1px solid var(--border);
  font-size: var(--fs-xs);
  font-weight: 700;
  color: var(--text-muted);
}
.sidebar__nav a:hover {
  background: var(--bg-subtle);
  color: var(--text);
}
.sidebar__nav a.is-active {
  background: var(--accent-soft);
  color: var(--accent);
  font-weight: 600;
}
.sidebar__nav a.is-active .num {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}

/* -------- Main content -------- */
.content {
  min-width: 0;
  padding: var(--sp-6) var(--sp-8);
}
.content__inner {
  max-width: var(--content-max);
  margin: 0 auto;
}

/* -------- On-page TOC (right rail) -------- */
.toc {
  position: sticky;
  top: var(--header-h);
  align-self: start;
  max-height: calc(100vh - var(--header-h));
  overflow-y: auto;
  padding: var(--sp-6) var(--sp-4);
  font-size: var(--fs-sm);
}
.toc__title {
  font-size: var(--fs-xs);
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--text-faint);
  margin: 0 0 var(--sp-3);
}
.toc__list {
  list-style: none;
  margin: 0;
  padding: 0;
  border-inline-start: 2px solid var(--border-subtle);
}
.toc__list a {
  display: block;
  padding: var(--sp-1) var(--sp-3);
  margin-inline-start: -2px;
  border-inline-start: 2px solid transparent;
  color: var(--text-muted);
  text-decoration: none;
  line-height: 1.5;
  transition: color 0.15s, border-color 0.15s;
}
.toc__list a:hover {
  color: var(--text);
}
.toc__list a.lvl-3 {
  padding-inline-start: var(--sp-5);
  font-size: var(--fs-xs);
}
.toc__list a.is-active {
  color: var(--accent);
  border-inline-start-color: var(--accent);
  font-weight: 600;
}

/* -------- Footer -------- */
.site-footer {
  border-top: 1px solid var(--border);
  background: var(--bg-subtle);
  color: var(--text-muted);
  font-size: var(--fs-sm);
}
.site-footer__inner {
  max-width: 1400px;
  margin: 0 auto;
  padding: var(--sp-6) var(--sp-8);
  display: flex;
  flex-wrap: wrap;
  gap: var(--sp-4);
  justify-content: space-between;
  align-items: center;
}
.site-footer a {
  color: var(--link);
  text-decoration: none;
}
.site-footer a:hover {
  text-decoration: underline;
}

/* -------- Sidebar overlay (mobile) -------- */
.sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  z-index: 90;
  background: rgba(0, 0, 0, 0.45);
}

/* ==========================================================================
   Responsive
   ========================================================================== */

/* Hide right-rail TOC on narrower viewports */
@media (max-width: 1180px) {
  .layout {
    grid-template-columns: var(--sidebar-w) minmax(0, 1fr);
  }
  .toc {
    display: none;
  }
}

/* Tablet / mobile: sidebar becomes an off-canvas drawer */
@media (max-width: 900px) {
  .layout {
    grid-template-columns: minmax(0, 1fr);
  }
  .menu-toggle {
    display: inline-flex;
  }
  .sidebar {
    position: fixed;
    top: var(--header-h);
    /* Logical start = right in RTL, left in LTR. Pin the drawer there. */
    inset-inline-start: 0;
    inset-inline-end: auto;
    z-index: 95;
    height: calc(100vh - var(--header-h));
    width: min(86vw, var(--sidebar-w));
    /* Hidden off the start edge. Transforms aren't logical, so flip per dir. */
    --drawer-hidden: -110%; /* LTR: hide off the left */
    transform: translateX(var(--drawer-hidden));
    transition: transform 0.25s ease;
    box-shadow: var(--shadow-lg);
  }
  html[dir="rtl"] .sidebar {
    --drawer-hidden: 110%; /* RTL: hide off the right */
  }
  body.sidebar-open .sidebar {
    transform: translateX(0);
  }
  body.sidebar-open .sidebar-overlay {
    display: block;
  }
  .content {
    padding: var(--sp-5) var(--sp-4);
  }
}

@media (max-width: 560px) {
  .site-header {
    padding: 0 var(--sp-3);
    gap: var(--sp-2);
  }
  .site-header__brand small {
    display: none;
  }
  .header-btn__label {
    display: none;
  }
  .content {
    padding: var(--sp-4) var(--sp-3);
  }
  .site-footer__inner {
    padding: var(--sp-5) var(--sp-4);
  }
}

/* ==========================================================================
   Mobile overflow hardening
   --------------------------------------------------------------------------
   Keep off-canvas UI and long LTR technical strings from widening the page.
   Code blocks, tables, and diagrams retain their own horizontal scroll.
   ========================================================================== */
html,
body {
  max-width: 100%;
  overflow-x: clip;
}

.site-header,
.site-header__brand,
.site-header__brand > span,
.content__inner,
.card,
.chapter-nav a {
  min-width: 0;
}

.site-header__brand > span {
  overflow: hidden;
  text-overflow: ellipsis;
}

img,
svg,
video {
  max-width: 100%;
}

.table-wrap,
.diagram,
.cheatsheet,
.code-block {
  max-width: 100%;
}

:not(pre) > code,
.sidebar__nav a,
.chapter-nav strong {
  overflow-wrap: anywhere;
}

@media (max-width: 560px) {
  .site-header__brand {
    flex: 1 1 auto;
  }

  .site-header__brand > span {
    display: block;
  }

  .card-grid,
  .highlights,
  .chapter-grid {
    grid-template-columns: minmax(0, 1fr);
  }

  .summary-box,
  .callout {
    padding: var(--sp-4);
  }
}

@media (max-width: 420px) {
  .site-header a[href^="https://github.com"] {
    display: none;
  }
}