:root{
  --paper:#eef3f3;
  --surface:#ffffff;
  --surface-2:#e4ecec;
  --ink:#16232a;
  --ink-soft:#425058;
  --border:#c7d6d6;
  --accent:#0f7a82;
  --accent-ink:#075a60;
  --accent-tint:#dcefef;
  --amber:#a8631f;
  --amber-tint:#f6e9d8;
  --mono-bg:#0f2a2c;
  --mono-ink:#d7ecec;
  --shadow: 0 1px 2px rgba(15,40,42,.08), 0 6px 20px -8px rgba(15,40,42,.18);
}
@media (prefers-color-scheme: dark){
  :root:not([data-theme="light"]){
    --paper:#0c1416;
    --surface:#121c1f;
    --surface-2:#182427;
    --ink:#dfeaea;
    --ink-soft:#a9bcbe;
    --border:#28393c;
    --accent:#3fc4cc;
    --accent-ink:#8fe1e6;
    --accent-tint:#122d2f;
    --amber:#e0954a;
    --amber-tint:#2c2115;
    --mono-bg:#08191a;
    --mono-ink:#bfe3e3;
    --shadow: 0 1px 2px rgba(0,0,0,.4), 0 10px 30px -12px rgba(0,0,0,.6);
  }
}
:root[data-theme="dark"]{
  --paper:#0c1416;
  --surface:#121c1f;
  --surface-2:#182427;
  --ink:#dfeaea;
  --ink-soft:#a9bcbe;
  --border:#28393c;
  --accent:#3fc4cc;
  --accent-ink:#8fe1e6;
  --accent-tint:#122d2f;
  --amber:#e0954a;
  --amber-tint:#2c2115;
  --mono-bg:#08191a;
  --mono-ink:#bfe3e3;
  --shadow: 0 1px 2px rgba(0,0,0,.4), 0 10px 30px -12px rgba(0,0,0,.6);
}

*{box-sizing:border-box;}
html{-webkit-text-size-adjust:100%;}
body{
  margin:0;
  background:var(--paper);
  color:var(--ink);
  font-family:"IBM Plex Sans","Helvetica Neue",Arial,sans-serif;
  line-height:1.55;
  font-size:16px;
}
h1,h2,h3,h4{
  font-family:"IBM Plex Sans Condensed","IBM Plex Sans",sans-serif;
  font-weight:700;
  color:var(--ink);
  text-wrap:balance;
  line-height:1.15;
}
code, .mono, .num, th, td.numcell, .badge, .glossterm{
  font-family:"IBM Plex Mono",ui-monospace,Menlo,Consolas,monospace;
  font-variant-numeric: tabular-nums;
}
a{color:var(--accent-ink);}
::selection{background:var(--accent-tint);}

/* ---------- Title block ---------- */
.titleblock{
  border-bottom:3px solid var(--ink);
  background:var(--surface);
}
.titleblock-inner{
  max-width:1180px;
  margin:0 auto;
  display:grid;
  grid-template-columns: 1fr auto;
  gap:0;
}
.tb-main{
  padding:28px 24px 20px;
  border-right:1px solid var(--border);
}
.tb-eyebrow{
  font-family:"IBM Plex Mono",monospace;
  font-size:12px;
  letter-spacing:.14em;
  text-transform:uppercase;
  color:var(--accent-ink);
  margin:0 0 8px;
}
.back-link{
  display:inline-flex;
  align-items:center;
  gap:6px;
  font-family:"IBM Plex Mono",monospace;
  font-size:12px;
  color:var(--ink-soft);
  text-decoration:none;
  margin:0 0 14px;
}
.back-link:hover{color:var(--accent-ink);}
.tb-title{
  font-size:clamp(28px,4vw,42px);
  margin:0 0 6px;
}
.tb-question{
  margin:10px 0 0;
  color:var(--ink-soft);
  font-size:16px;
  max-width:60ch;
}
.tb-stamp{
  display:grid;
  grid-template-columns:repeat(2,minmax(90px,1fr));
  font-family:"IBM Plex Mono",monospace;
  font-size:12px;
}
.tb-cell{
  padding:10px 16px;
  border-bottom:1px solid var(--border);
  border-left:1px solid var(--border);
}
.tb-cell:nth-child(odd){border-left:none;}
.tb-cell .k{display:block;color:var(--ink-soft);letter-spacing:.06em;text-transform:uppercase;font-size:10px;margin-bottom:4px;}
.tb-cell .v{color:var(--ink);font-weight:600;}

/* ---------- Layout ---------- */
.layout{
  max-width:1180px;
  margin:0 auto;
  display:grid;
  grid-template-columns: 230px minmax(0,1fr);
  gap:40px;
  padding:32px 24px 80px;
  align-items:start;
}
nav.toc{
  position:sticky;
  top:20px;
  border:1px solid var(--border);
  background:var(--surface);
  border-radius:10px;
  padding:16px;
  box-shadow:var(--shadow);
}
nav.toc h2{
  font-size:11px;
  letter-spacing:.1em;
  text-transform:uppercase;
  color:var(--ink-soft);
  margin:0 0 10px;
}
nav.toc ol{list-style:none;margin:0;padding:0;display:flex;flex-direction:column;gap:2px;}
nav.toc li a{
  display:block;
  padding:6px 8px;
  border-radius:6px;
  color:var(--ink-soft);
  text-decoration:none;
  font-size:13.5px;
}
nav.toc li a .n{color:var(--accent-ink);font-family:"IBM Plex Mono",monospace;margin-right:6px;}
nav.toc li a:hover{background:var(--surface-2);color:var(--ink);}
nav.toc li.sep{height:1px;background:var(--border);margin:8px 2px;}

main{min-width:0;}

/* ---------- Content blocks ---------- */
section.topic{margin-bottom:56px;scroll-margin-top:20px;}
.topic-head{
  display:flex;
  align-items:baseline;
  gap:14px;
  border-bottom:2px solid var(--ink);
  padding-bottom:10px;
  margin-bottom:18px;
}
.topic-head .code{
  font-family:"IBM Plex Mono",monospace;
  font-size:14px;
  color:var(--surface);
  background:var(--accent-ink);
  padding:3px 9px;
  border-radius:4px;
  white-space:nowrap;
}
.topic-head h2{font-size:24px;margin:0;}

.definition{
  background:var(--surface);
  border:1px solid var(--border);
  border-left:4px solid var(--accent);
  border-radius:8px;
  padding:16px 18px;
  margin:0 0 16px;
  box-shadow:var(--shadow);
}
.definition .label{
  font-size:11px;
  letter-spacing:.08em;
  text-transform:uppercase;
  color:var(--accent-ink);
  margin:0 0 6px;
  font-weight:700;
}
.definition p{margin:0;}
.definition + .definition{margin-top:-8px;}

.objective{
  font-size:14.5px;
  color:var(--ink-soft);
  border-left:3px solid var(--border);
  padding-left:12px;
  margin:0 0 22px;
}
.objective b{color:var(--ink);}

h3.sub{font-size:17px;margin:26px 0 10px;}
p{margin:0 0 14px;max-width:72ch;}
ul,ol.list{margin:0 0 14px;padding-left:22px;max-width:72ch;}
li{margin-bottom:6px;}

.examples{
  background:var(--surface);
  border:1px solid var(--border);
  border-radius:8px;
  padding:14px 18px;
  margin:16px 0;
}
.examples .label{font-size:11px;letter-spacing:.08em;text-transform:uppercase;color:var(--ink-soft);font-weight:700;margin-bottom:8px;}
.examples ul{margin:0;padding-left:20px;}

.term-row{
  display:grid;
  grid-template-columns:200px 1fr;
  gap:14px;
  padding:12px 0;
  border-bottom:1px solid var(--border);
}
.term-row:last-child{border-bottom:none;}
.term-row .glossterm{color:var(--accent-ink);font-weight:600;font-size:14px;}
.term-row p{margin:0;font-size:14.5px;max-width:60ch;}

.callout{
  background:var(--amber-tint);
  border:1px solid var(--amber);
  border-radius:8px;
  padding:16px 18px;
  margin:18px 0;
}
.callout .label{
  font-size:11px;letter-spacing:.08em;text-transform:uppercase;
  color:var(--amber);font-weight:700;margin:0 0 8px;
  display:flex;align-items:center;gap:8px;
}
.callout ul{margin:0;padding-left:20px;}
.callout li{margin-bottom:8px;font-size:14.5px;}

/* diagrams */
.flowdiagram{
  display:flex;
  flex-wrap:wrap;
  align-items:stretch;
  gap:8px 0;
  margin:20px 0;
}
.flowbox{
  flex:1 1 130px;
  background:var(--surface);
  border:1.5px solid var(--ink);
  border-radius:6px;
  padding:14px 12px;
  font-size:13px;
  text-align:center;
  display:flex;
  align-items:center;
  justify-content:center;
  min-height:64px;
}
.flowarrow{
  flex:0 0 30px;
  display:flex;
  align-items:center;
  justify-content:center;
  color:var(--accent-ink);
  font-size:20px;
}
@media (max-width:640px){
  .flowdiagram{flex-direction:column;gap:0;}
  .flowbox{flex:1 1 auto;width:100%;}
  .flowarrow{flex:0 0 auto;width:100%;transform:rotate(90deg);padding:2px 0;}
}
.flowdiagram + .flowdiagram{margin-top:10px;}
.diagram-caption{font-size:12.5px;color:var(--ink-soft);margin-top:-8px;margin-bottom:20px;}

.chart-wrap{
  background:var(--surface);
  border:1px solid var(--border);
  border-radius:10px;
  padding:18px;
  margin:20px 0;
  box-shadow:var(--shadow);
}
.chart-wrap svg{width:100%;height:auto;display:block;}
.chart-title{font-size:13px;font-weight:700;margin:0 0 4px;}
.chart-note{font-size:12.5px;color:var(--ink-soft);margin:8px 0 0;}

/* glossary table */
table.glossary{width:100%;border-collapse:collapse;margin:10px 0 8px;}
table.glossary th{
  text-align:left;font-size:11px;text-transform:uppercase;letter-spacing:.06em;
  color:var(--ink-soft);border-bottom:2px solid var(--ink);padding:8px 10px 8px 0;
}
table.glossary td{padding:12px 10px 12px 0;border-bottom:1px solid var(--border);vertical-align:top;font-size:14px;}
table.glossary td:first-child{white-space:nowrap;color:var(--accent-ink);font-weight:600;}
.table-scroll{overflow-x:auto;}

/* practice questions */
.qcard{
  background:var(--surface);
  border:1px solid var(--border);
  border-radius:8px;
  padding:16px 18px;
  margin-bottom:14px;
}
.qcard .qn{font-family:"IBM Plex Mono",monospace;color:var(--accent-ink);font-size:13px;margin-right:8px;}
.qcard p.q{margin:0 0 8px;font-weight:600;}
.qcard ul.opts{margin:0 0 10px;padding-left:20px;font-size:14.5px;}
.qcard details{margin-top:6px;}
.qcard summary{
  cursor:pointer;font-size:13px;color:var(--accent-ink);font-weight:600;
  list-style:none;display:inline-flex;align-items:center;gap:6px;
}
.qcard summary::-webkit-details-marker{display:none;}
.qcard summary::before{content:"▸";transition:transform .15s;}
.qcard details[open] summary::before{transform:rotate(90deg);}
.qcard .answer{
  margin-top:10px;padding:10px 12px;background:var(--accent-tint);border-radius:6px;font-size:14px;
}

.linkq{
  display:grid;grid-template-columns:auto 1fr;gap:10px 14px;margin:0;padding:0;list-style:none;
}
.linkq li{display:contents;}
.linkq .tag{
  font-family:"IBM Plex Mono",monospace;font-size:12px;background:var(--surface-2);color:var(--ink-soft);
  padding:3px 8px;border-radius:5px;height:fit-content;white-space:nowrap;
}
.linkq .qtext{font-size:14.5px;padding-bottom:10px;border-bottom:1px solid var(--border);}

footer.sources{
  border-top:2px solid var(--ink);
  padding-top:18px;
  margin-top:50px;
  font-size:13px;
  color:var(--ink-soft);
}
footer.sources b{color:var(--ink);}

/* mobile */
@media (max-width:900px){
  .layout{grid-template-columns:1fr;padding:20px 16px 60px;gap:20px;}
  nav.toc{position:static;}
    .titleblock-inner{grid-template-columns:1fr;}
  .tb-main{border-right:none;border-bottom:1px solid var(--border);}
  .tb-stamp{grid-template-columns:repeat(2,1fr);}
  .term-row{grid-template-columns:1fr;gap:4px;}
  .linkq{grid-template-columns:1fr;}
  .linkq .tag{width:fit-content;}
}
@media (prefers-reduced-motion:reduce){*{transition:none!important;animation:none!important;}}

.stamp-print{display:none;}

@media print{
  nav.toc{display:none!important;}
  .layout{grid-template-columns:1fr!important;padding:0!important;gap:0!important;max-width:100%!important;}
  body{background:#fff;font-size:12.5px;}
  .titleblock{border-bottom-color:#000;}
  a{color:inherit;text-decoration:none;}
  .chart-wrap,.definition,.examples,.callout,.qcard,table.glossary{box-shadow:none!important;}
  section.topic{margin-bottom:26px;break-inside:avoid-page;}
  .term-row,.qcard,.chart-wrap,.definition{break-inside:avoid-page;}
  .qcard details{display:block!important;}
  .qcard summary{display:none!important;}
  .qcard .answer{background:#f1f1f1!important;-webkit-print-color-adjust:exact;print-color-adjust:exact;}
  .callout{-webkit-print-color-adjust:exact;print-color-adjust:exact;}
  nav.toc{display:none!important;}
  .hide-print{display:none!important;}
  .stamp-screen{display:none!important;}
  .stamp-print{display:grid!important;}
  .stamp-print a{text-decoration:underline;color:inherit;}
}

/* ---------- flashcards ---------- */
.flash-open-btn{
  display:flex;align-items:center;justify-content:center;gap:6px;
  width:100%;margin-bottom:14px;padding:10px 12px;
  border:1px solid var(--accent);border-radius:8px;
  background:var(--accent-tint);color:var(--accent-ink);
  font:inherit;font-weight:600;font-size:13.5px;cursor:pointer;
}
.flash-open-btn:hover{background:var(--accent);color:#fff;}
.flash-open-btn .flash-count{font-weight:400;opacity:.8;font-size:12px;}

.flash-modal{
  position:fixed;inset:0;z-index:100;
  display:flex;align-items:center;justify-content:center;
  background:rgba(12,20,22,.55);padding:20px;
}
.flash-modal[hidden]{display:none;}
.flash-panel{
  width:100%;max-width:640px;max-height:90vh;
  display:flex;flex-direction:column;
  background:var(--surface);border:1px solid var(--border);border-radius:14px;
  box-shadow:var(--shadow);overflow:hidden;
}
.flash-head{
  display:flex;align-items:center;gap:10px;flex-wrap:wrap;
  padding:14px 18px;border-bottom:1px solid var(--border);
}
.flash-head h2{margin:0;font-size:16px;flex:1 0 auto;}
.flash-head select{
  font:inherit;font-size:13px;padding:6px 8px;border-radius:6px;
  border:1px solid var(--border);background:var(--surface);color:var(--ink);
}
.flash-icon-btn{
  font:inherit;font-size:13px;padding:6px 10px;border-radius:6px;
  border:1px solid var(--border);background:var(--surface-2);color:var(--ink);cursor:pointer;
}
.flash-close{
  width:30px;height:30px;border-radius:50%;border:1px solid var(--border);
  background:var(--surface-2);color:var(--ink);cursor:pointer;font-size:14px;line-height:1;
}
.flash-meta{
  display:flex;justify-content:space-between;gap:10px;
  padding:10px 18px 0;font-size:12.5px;color:var(--ink-soft);
}
.flash-progress-track{
  margin:8px 18px 0;height:5px;border-radius:3px;background:var(--surface-2);overflow:hidden;
}
.flash-progress-fill{height:100%;width:0;background:var(--accent);transition:width .2s;}
.flash-body{padding:18px;overflow-y:auto;flex:1 1 auto;}

.flash-card{perspective:1400px;min-height:220px;margin-bottom:18px;cursor:pointer;}
.flash-card-inner{
  position:relative;width:100%;height:220px;
  transform-style:preserve-3d;transition:transform .45s;
}
.flash-card.flipped .flash-card-inner{transform:rotateY(180deg);}
.flash-face{
  position:absolute;inset:0;backface-visibility:hidden;
  display:flex;flex-direction:column;align-items:center;justify-content:center;
  gap:10px;text-align:center;padding:22px;
  border:1px solid var(--border);border-radius:12px;
  background:var(--surface-2);
}
.flash-face.flash-back{transform:rotateY(180deg);background:var(--accent-tint);}
.flash-kind{
  font-size:10.5px;letter-spacing:.08em;text-transform:uppercase;
  color:var(--accent-ink);font-weight:700;
}
.flash-text{margin:0;font-size:15.5px;line-height:1.5;white-space:pre-line;}
.flash-hint{font-size:11.5px;color:var(--ink-soft);}

.flash-controls{display:flex;gap:8px;flex-wrap:wrap;}
.flash-btn{
  flex:1 1 0;min-width:90px;font:inherit;font-size:13.5px;font-weight:600;
  padding:10px 10px;border-radius:8px;border:1px solid var(--border);
  background:var(--surface-2);color:var(--ink);cursor:pointer;
}
.flash-btn.flash-nav{flex-grow:0.7;font-weight:500;}
.flash-btn.flash-no{background:var(--amber-tint);border-color:var(--amber);color:var(--amber);}
.flash-btn.flash-yes{background:var(--accent);border-color:var(--accent);color:#fff;}

.flash-foot{
  display:flex;align-items:center;justify-content:space-between;gap:10px;flex-wrap:wrap;
  padding:10px 18px;border-top:1px solid var(--border);
  font-size:11.5px;color:var(--ink-soft);
}
.flash-foot button{
  font:inherit;font-size:12px;padding:6px 10px;border-radius:6px;
  border:1px solid var(--border);background:transparent;color:var(--ink-soft);cursor:pointer;
}
.flash-done{text-align:center;padding:30px 10px;}
.flash-done h3{margin:0 0 8px;}
.flash-done .flash-btn{display:inline-flex;margin-top:12px;min-width:160px;flex:none;}

@media (max-width:640px){
  .flash-panel{max-height:94vh;}
  .flash-card-inner{height:260px;}
  .flash-head h2{flex:1 1 100%;}
}
@media print{
  .flash-open-btn,.flash-modal{display:none!important;}
}

/* ---------- modo estudio ---------- */
.study-open-btn{
  display:flex;align-items:center;justify-content:center;gap:6px;
  width:100%;margin-bottom:14px;padding:10px 12px;
  border:1px solid var(--amber);border-radius:8px;
  background:var(--amber-tint);color:var(--amber);
  font:inherit;font-weight:600;font-size:13.5px;cursor:pointer;
}
.study-open-btn:hover{background:var(--amber);color:#fff;}
.study-open-btn[aria-pressed="true"]{background:var(--amber);color:#fff;}

.study-banner{
  margin:0 0 18px;padding:10px 14px;
  border:1px solid var(--amber);border-radius:8px;
  background:var(--amber-tint);color:var(--ink);
  font-size:13.5px;line-height:1.5;
}
.study-topic{padding:14px 0;}
.study-topic .topic-head{margin-bottom:8px;}
.study-topic .definition{padding:8px 12px;margin-bottom:8px;}
.study-list{margin:0;padding-left:20px;}
.study-list li{margin-bottom:7px;line-height:1.48;font-size:14.5px;}
.study-list li:last-child{margin-bottom:0;}

@media print{
  .study-open-btn{display:none!important;}
}