/* ===========================================================================
   Tushar Madan — site design system
   Palette + layout borrowed from concord-architecture; mono typography (Chivo
   Mono) borrowed from iii.dev.
   =========================================================================== */

:root {
  --paper: #F4F7FB;
  --paper-2: #E8EFF6;
  --panel: #FBFCFE;
  --panel-2: #EEF3F9;
  --ink: #11212B;
  --ink-soft: #2A3A44;
  --muted: #566571;
  --muted-2: #8496A3;
  --line: #D9E2EC;
  --line-strong: #C0CDDA;
  --teal: #15A39C;
  --teal-deep: #0D7C77;
  --teal-soft: #BCE4E1;
  --teal-bg: #E2F3F1;
  --sage: #4E8C84;
  --plum: #4F6D7A;
  --code-bg: #EEF3F8;
  --inline-code: #E6EDF6;

  --sans: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  --serif: 'Source Serif 4', Georgia, 'Times New Roman', serif;
  --mono: 'Chivo Mono', ui-monospace, 'JetBrains Mono', monospace;
  --code: 'JetBrains Mono', ui-monospace, 'Chivo Mono', monospace;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.7;
  color: var(--ink);
  background: var(--paper);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
}

a { color: var(--teal-deep); text-decoration: none; }
a:hover { color: var(--teal); }

/* ---------------------------------------------------------------- layout --- */

.layout {
  display: grid;
  grid-template-columns: 280px minmax(0, 1fr);
  max-width: 1280px;
  margin: 0 auto;
  gap: 0;
}

/* post view adds a right rail */
.layout.with-rail {
  grid-template-columns: 260px minmax(0, 1fr) 260px;
  max-width: 1440px;
}

/* ----------------------------------------------------------------- sidebar - */

.sidebar {
  position: sticky;
  top: 0;
  align-self: start;
  height: 100vh;
  overflow-y: auto;
  padding: 56px 32px 56px 40px;
  border-right: 1px solid var(--line);
}
.sidebar::-webkit-scrollbar { width: 4px; }
.sidebar::-webkit-scrollbar-thumb { background: var(--line-strong); border-radius: 2px; }

.brand {
  font-family: var(--serif);
  font-size: 24px;
  font-weight: 500;
  letter-spacing: -0.02em;
  color: var(--ink);
  margin: 0 0 4px;
  display: inline-block;
}
.brand:hover { color: var(--ink); }
.brand-mark {
  display: inline-block;
  width: 7px; height: 7px;
  background: var(--teal);
  border-radius: 50%;
  margin-right: 10px;
  vertical-align: middle;
  transform: translateY(-2px);
}
.brand-sub {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--muted);
  margin: 0 0 36px;
  letter-spacing: 0.02em;
}

.nav-label {
  font-family: var(--mono);
  font-size: 10px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.14em;
  color: var(--muted-2);
  margin: 28px 0 12px;
}
.nav { display: flex; flex-direction: column; }
.nav a {
  display: block;
  padding: 5px 0 5px 12px;
  font-size: 13.5px;
  color: var(--muted);
  border-left: 1px solid var(--line);
  transition: color 0.15s ease, border-color 0.15s ease;
}
.nav a:hover { color: var(--ink); border-left-color: var(--teal); }
.nav a.active { color: var(--ink); border-left-color: var(--teal); font-weight: 500; }
.nav a .tag { font-family: var(--mono); font-size: 10px; color: var(--muted-2); }

.sidebar-foot {
  margin-top: 36px;
  padding-top: 20px;
  border-top: 1px solid var(--line);
  font-family: var(--mono);
  font-size: 11px;
  color: var(--muted-2);
  line-height: 1.9;
}
.sidebar-foot a { color: var(--muted); }
.sidebar-foot a:hover { color: var(--teal); }

/* -------------------------------------------------------------------- main - */

main {
  padding: clamp(48px, 7vw, 80px) clamp(20px, 6vw, 72px) 120px;
  min-width: 0;
}

/* home: single-screen landing, hero centred in the viewport */
.home {
  display: flex;
  flex-direction: column;
  justify-content: center;
  min-height: 100vh;
  padding-block: 0;
}
.home .hero { margin: 0; padding: 0; border-bottom: none; }

/* ----------------------------------------------------------------- hero --- */

.hero {
  margin-bottom: 72px;
  padding-bottom: 48px;
  border-bottom: 1px solid var(--line);
}
.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-family: var(--mono);
  font-size: 11px;
  font-weight: 500;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--teal);
  margin-bottom: 26px;
}
.eyebrow::before {
  content: '';
  width: 24px; height: 1px;
  background: var(--teal);
}
.hero h1 {
  font-family: var(--serif);
  font-size: clamp(44px, 10vw, 84px);
  font-weight: 400;
  line-height: 1;
  letter-spacing: -0.035em;
  margin: 0 0 24px;
  color: var(--ink);
}
.hero-tagline {
  font-family: var(--serif);
  font-size: clamp(18px, 3.6vw, 23px);
  line-height: 1.45;
  font-weight: 300;
  color: var(--ink-soft);
  margin: 0 0 36px;
  max-width: 640px;
  letter-spacing: -0.01em;
}
.hero-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 32px;
  font-size: 13px;
  color: var(--muted);
}
.meta-item strong {
  display: block;
  font-family: var(--mono);
  font-size: 10px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--muted-2);
  margin-bottom: 4px;
}
.meta-item span { color: var(--ink); font-weight: 500; font-size: 14px; }
.meta-item a { font-weight: 500; font-size: 14px; }

/* page title (blog / sub pages) */
.page-head { margin-bottom: 56px; padding-bottom: 36px; border-bottom: 1px solid var(--line); }
.page-head h1 {
  font-family: var(--serif);
  font-size: clamp(34px, 8vw, 56px);
  font-weight: 400;
  line-height: 1.05;
  letter-spacing: -0.03em;
  margin: 12px 0 16px;
}
.page-head p { font-family: var(--serif); font-size: 19px; font-weight: 300; color: var(--ink-soft); max-width: 60ch; margin: 0; }

/* ------------------------------------------------------- collapsible -------- */

details.section { border-bottom: 1px solid var(--line); }
details.section:last-of-type { border-bottom: none; }
details.section[open] { padding-bottom: 32px; }

summary.section-head {
  list-style: none;
  cursor: pointer;
  padding: 32px 56px 32px 0;
  position: relative;
  user-select: none;
}
summary.section-head::-webkit-details-marker { display: none; }
summary.section-head .section-title {
  display: block;
  font-family: var(--serif);
  font-size: 30px;
  font-weight: 400;
  line-height: 1.15;
  letter-spacing: -0.02em;
  color: var(--ink);
  transition: color 0.15s ease;
}
details.section[open] summary.section-head { padding-bottom: 8px; }
summary.section-head:hover .section-title { color: var(--teal-deep); }
summary.section-head .chevron {
  position: absolute;
  top: 44px; right: 10px;
  width: 9px; height: 9px;
  border-right: 1.5px solid var(--muted-2);
  border-bottom: 1.5px solid var(--muted-2);
  transform: rotate(45deg);
  transition: transform 0.25s ease, border-color 0.15s ease;
}
details.section[open] summary.section-head .chevron { transform: rotate(-135deg); top: 48px; }
summary.section-head:hover .chevron { border-color: var(--teal); }

.section-body > :where(p, ul, ol, blockquote) { max-width: 68ch; }

/* --------------------------------------------------------------- cards ----- */

.section-group { margin-bottom: 64px; }
.section-group > .group-label {
  font-family: var(--mono);
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.14em;
  color: var(--teal);
  margin: 0 0 16px;
}

.post-list { display: flex; flex-direction: column; }
.post-row {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 24px;
  padding: 14px 0;
  border-top: 1px solid var(--line);
  transition: border-color 0.15s ease;
}
.post-row:last-child { border-bottom: 1px solid var(--line); }
.post-row:hover { border-top-color: var(--teal); }
.post-row .post-name {
  font-family: var(--serif);
  font-size: 20px;
  font-weight: 400;
  letter-spacing: -0.01em;
  color: var(--ink);
  line-height: 1.3;
  transition: color 0.15s ease;
}
.post-row:hover .post-name { color: var(--teal-deep); }
.post-row .post-date {
  flex: none;
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.04em;
  color: var(--muted-2);
}
.tag-pill {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.04em;
  color: var(--muted);
  background: var(--panel-2);
  border: 1px solid var(--line);
  border-radius: 100px;
  padding: 2px 10px;
}

.empty-note { font-family: var(--mono); font-size: 12px; color: var(--muted-2); padding: 20px 0; border-top: 1px solid var(--line); }

/* --------------------------------------------------------------- article --- */

.article { max-width: 72ch; }
.article-eyebrow {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--teal);
  margin-bottom: 18px;
}
.article-title {
  font-family: var(--serif);
  font-size: clamp(32px, 8vw, 52px);
  font-weight: 400;
  line-height: 1.06;
  letter-spacing: -0.03em;
  margin: 0 0 20px;
}
.article-sub {
  font-family: var(--serif);
  font-size: 19px;
  font-weight: 300;
  color: var(--ink-soft);
  margin: 0 0 28px;
}
.article-meta {
  display: flex;
  gap: 20px;
  flex-wrap: wrap;
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.04em;
  color: var(--muted-2);
  padding-bottom: 36px;
  margin-bottom: 44px;
  border-bottom: 1px solid var(--line);
}

/* prose */
.prose { font-size: 16.5px; line-height: 1.78; color: var(--ink-soft); }
.prose h2 {
  font-family: var(--serif);
  font-size: 32px;
  font-weight: 400;
  letter-spacing: -0.02em;
  line-height: 1.2;
  margin: 56px 0 18px;
  color: var(--ink);
  scroll-margin-top: 24px;
}
.prose h3 {
  font-family: var(--serif);
  font-size: 23px;
  font-weight: 500;
  letter-spacing: -0.01em;
  margin: 40px 0 14px;
  color: var(--ink);
  scroll-margin-top: 24px;
}
.prose h4 {
  font-family: var(--mono);
  font-size: 12px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--muted);
  margin: 32px 0 10px;
}
.prose p { margin: 0 0 20px; }
.prose ul, .prose ol { margin: 0 0 20px; padding-left: 24px; }
.prose li { margin: 6px 0; }
.prose a { border-bottom: 1px solid var(--teal-soft); }
.prose a:hover { border-bottom-color: var(--teal); }
.prose img { max-width: 100%; border-radius: 6px; border: 1px solid var(--line); }
.prose hr { border: none; border-top: 1px solid var(--line); margin: 48px 0; }

.prose blockquote {
  margin: 28px 0;
  padding: 4px 0 4px 24px;
  border-left: 2px solid var(--teal);
  font-family: var(--serif);
  font-style: italic;
  font-size: 19px;
  color: var(--ink-soft);
}

/* code */
.prose code {
  font-family: var(--code);
  font-size: 0.88em;
  background: var(--inline-code);
  border: 1px solid var(--line);
  border-radius: 4px;
  padding: 1px 5px;
}
.prose pre {
  background: var(--code-bg);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 18px 20px;
  overflow-x: auto;
  margin: 24px 0;
  font-size: 13.5px;
  line-height: 1.6;
}
.prose pre code {
  font-family: var(--code);
  background: none;
  border: none;
  padding: 0;
  font-size: inherit;
}

/* tables */
.prose table { width: 100%; border-collapse: collapse; margin: 24px 0; font-size: 14.5px; }
.prose th, .prose td { text-align: left; padding: 10px 14px; border-bottom: 1px solid var(--line); }
.prose th { font-family: var(--mono); font-size: 11px; text-transform: uppercase; letter-spacing: 0.06em; color: var(--muted); }

/* KaTeX */
.prose .katex-display { margin: 28px 0; overflow-x: auto; overflow-y: hidden; padding: 4px 0; }
.prose .katex { font-size: 1.05em; }

/* mermaid */
.prose .mermaid { margin: 28px 0; text-align: center; }

/* embedded interactive simulations (iframes) */
.prose .embed { margin: 36px 0; }
.prose .embed-frame {
  display: block;
  width: 100%;
  border: none;
  height: 640px; /* fallback before postMessage auto-resize fires */
  overflow: hidden;
}

/* ------------------------------------------------------------- right rail -- */

.rail {
  position: sticky;
  top: 0;
  align-self: start;
  height: 100vh;
  overflow-y: auto;
  padding: 88px 32px 56px 36px;
  border-left: 1px solid var(--line);
}
.rail::-webkit-scrollbar { width: 4px; }
.rail::-webkit-scrollbar-thumb { background: var(--line-strong); border-radius: 2px; }
.rail-label {
  font-family: var(--mono);
  font-size: 10px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.14em;
  color: var(--muted-2);
  margin: 0 0 14px;
}
.toc { display: flex; flex-direction: column; margin-bottom: 36px; }
.toc a {
  display: block;
  padding: 4px 0 4px 12px;
  font-size: 12.5px;
  color: var(--muted);
  border-left: 1px solid var(--line);
  line-height: 1.4;
  transition: color 0.15s ease, border-color 0.15s ease;
}
.toc a.lvl-3 { padding-left: 24px; font-size: 12px; }
.toc a:hover { color: var(--ink); border-left-color: var(--teal); }
.toc a.active { color: var(--teal-deep); border-left-color: var(--teal); font-weight: 500; }

.rail-meta { border-top: 1px solid var(--line); padding-top: 20px; font-family: var(--mono); font-size: 11px; color: var(--muted); line-height: 2; }
.rail-meta .k { color: var(--muted-2); text-transform: uppercase; letter-spacing: 0.06em; font-size: 10px; }
.rail-back { display: inline-block; margin-top: 24px; font-family: var(--mono); font-size: 11px; letter-spacing: 0.04em; color: var(--muted); }
.rail-back:hover { color: var(--teal); }

/* --------------------------------------------------------------- states ---- */

.loading, .error { font-family: var(--mono); font-size: 13px; color: var(--muted-2); padding: 40px 0; }
.error { color: var(--teal-deep); }

/* ------------------------------------------------------------- responsive -- */

@media (max-width: 1100px) {
  .layout.with-rail { grid-template-columns: 240px minmax(0, 1fr); }
  .layout.with-rail .rail { display: none; }
}
@media (max-width: 820px) {
  .layout, .layout.with-rail { grid-template-columns: 1fr; }

  /* sidebar collapses into a slim sticky top bar */
  .sidebar {
    position: sticky;
    top: 0;
    z-index: 20;
    height: auto;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 16px;
    padding: 12px 20px;
    background: var(--paper);
    border-right: none;
    border-bottom: 1px solid var(--line);
  }
  .brand { font-size: 18px; margin: 0; }
  .brand-mark { width: 6px; height: 6px; margin-right: 7px; transform: translateY(-1px); }
  .brand-sub,
  .nav-label,
  .sidebar-foot,
  .sidebar nav:nth-of-type(2) { display: none; }

  .sidebar nav:first-of-type { flex-direction: row; gap: 20px; margin: 0; }
  .sidebar nav:first-of-type a {
    border-left: none;
    padding: 0;
    font-size: 14px;
  }
  .sidebar nav:first-of-type a.active { border-left: none; color: var(--teal-deep); }

  /* keep anchored headings clear of the sticky bar */
  .prose h2, .prose h3 { scroll-margin-top: 68px; }

  /* home: let the hero sit naturally rather than force full height under the bar */
  .home { min-height: auto; justify-content: flex-start; padding-block: clamp(48px, 14vw, 96px); }
}