:root{
  --paper:#faf8f2; --surface:#ffffff; --surface-2:#f4f1e8;
  --ink:#22262c; --ink-soft:#565c66; --ink-faint:#8a8f99;
  --navy:#123a63; --navy-deep:#0e2b4a; --navy-band:#143559; --navy-text:#123a63;
  --maroon:#8e2130;
  --gold:#c0972f; --cream:#f8f0d6; --cream-bar:#efdfad;
  --mint:#e7f1e8; --mint-line:#c1d8c5;
  --blue:#e9f2fa; --blue-line:#bcd8ec;
  --rule:#ddd6c6; --rule-strong:#b7ae99;
  --soon:#9a8a5e; --soon-bg:#f2ecdb;
  --shadow:0 1px 2px rgba(20,40,70,.06),0 8px 22px rgba(20,40,70,.06);
  --shadow-h:0 4px 10px rgba(20,40,70,.10),0 16px 40px rgba(20,40,70,.12);
}
@media (prefers-color-scheme:dark){:root:not([data-theme="light"]){
  --paper:#0d151f; --surface:#152230; --surface-2:#101b26;
  --ink:#e7ebf1; --ink-soft:#aab4c0; --ink-faint:#7c8794;
  --navy:#7fb2e6; --navy-deep:#0b1928; --navy-band:#123157; --navy-text:#9cc4ee;
  --maroon:#e88a97;
  --gold:#caa64a; --cream:#241f12; --cream-bar:#33290f;
  --mint:#15271c; --mint-line:#2c4633;
  --blue:#122534; --blue-line:#274763;
  --rule:#28323f; --rule-strong:#3a4759;
  --soon:#9a8a5e; --soon-bg:#241f12;
  --shadow:0 1px 2px rgba(0,0,0,.3),0 8px 24px rgba(0,0,0,.28);
  --shadow-h:0 6px 16px rgba(0,0,0,.4),0 20px 46px rgba(0,0,0,.4);
}}
:root[data-theme="dark"]{
  --paper:#0d151f; --surface:#152230; --surface-2:#101b26;
  --ink:#e7ebf1; --ink-soft:#aab4c0; --ink-faint:#7c8794;
  --navy:#7fb2e6; --navy-deep:#0b1928; --navy-band:#123157; --navy-text:#9cc4ee;
  --maroon:#e88a97;
  --gold:#caa64a; --cream:#241f12; --cream-bar:#33290f;
  --mint:#15271c; --mint-line:#2c4633;
  --blue:#122534; --blue-line:#274763;
  --rule:#28323f; --rule-strong:#3a4759;
  --soon:#b3a06a; --soon-bg:#241f12;
  --shadow:0 1px 2px rgba(0,0,0,.3),0 8px 24px rgba(0,0,0,.28);
  --shadow-h:0 6px 16px rgba(0,0,0,.4),0 20px 46px rgba(0,0,0,.4);
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{background:var(--paper);color:var(--ink);margin:0;
  font-family:"Source Serif 4",Georgia,"Times New Roman",serif;font-size:18px;line-height:1.6;-webkit-font-smoothing:antialiased}
@media (prefers-reduced-motion:reduce){html{scroll-behavior:auto}}

/* top bar */
.topbar{display:flex;align-items:center;justify-content:space-between;gap:12px;padding:12px 22px;
  background:var(--navy-band);color:#fff;border-bottom:3px solid var(--gold);flex-wrap:wrap}
.topbar a{color:#fff;text-decoration:none}
.topbar .brand{font-family:"IBM Plex Sans",sans-serif;font-weight:700;letter-spacing:.1em;text-transform:uppercase;font-size:15px}
.topbar .brand span{opacity:.8;font-weight:500}
.topbar nav{display:flex;gap:16px;font-family:"IBM Plex Sans",sans-serif;font-size:13.5px}
.topbar nav a{opacity:.9}.topbar nav a:hover{opacity:1;text-decoration:underline}

/* hero */
.hero{max-width:1080px;margin:0 auto;padding:52px 24px 22px;text-align:center}
.hero .eyebrow{font-family:"IBM Plex Sans",sans-serif;font-size:12.5px;letter-spacing:.16em;text-transform:uppercase;
  color:var(--maroon);font-weight:600;margin-bottom:12px}
.hero h1{font-size:clamp(38px,7.5vw,60px);font-weight:700;color:var(--navy-text);margin:0 0 12px;letter-spacing:-.01em;line-height:1.03;text-wrap:balance}
.hero p{font-size:clamp(17px,2.6vw,21px);color:var(--ink-soft);max-width:640px;margin:0 auto;line-height:1.5}

/* controls */
.controls{max-width:1080px;margin:26px auto 0;padding:0 24px;display:flex;gap:14px;align-items:center;flex-wrap:wrap;justify-content:space-between}
.search{position:relative;flex:1;min-width:220px;max-width:360px}
.search input{width:100%;font-family:"Source Serif 4",serif;font-size:15.5px;padding:9px 14px 9px 34px;
  border:1px solid var(--rule-strong);border-radius:22px;background:var(--surface);color:var(--ink)}
.search input:focus{outline:2px solid var(--gold);outline-offset:1px;border-color:var(--navy)}
.search::before{content:"⌕";position:absolute;left:13px;top:7px;font-size:17px;color:var(--ink-faint)}
.chips{display:flex;gap:8px;flex-wrap:wrap;font-family:"IBM Plex Sans",sans-serif}
.chip{font-size:13px;padding:6px 13px;border:1px solid var(--rule-strong);border-radius:20px;background:var(--surface);
  color:var(--ink-soft);cursor:pointer;font-weight:500}
.chip:hover{border-color:var(--navy);color:var(--navy-text)}
.chip.active{background:var(--navy-band);color:#fff;border-color:var(--navy-band)}
.countline{max-width:1080px;margin:16px auto 0;padding:0 24px;font-family:"IBM Plex Sans",sans-serif;font-size:13px;color:var(--ink-faint)}

/* grid */
.grid{max-width:1080px;margin:12px auto 0;padding:8px 24px 20px;display:grid;grid-template-columns:repeat(auto-fill,minmax(300px,1fr));gap:18px}
.tcard{display:flex;flex-direction:column;border:1px solid var(--rule);border-radius:12px;background:var(--surface);
  padding:20px;box-shadow:var(--shadow);transition:transform .16s ease,box-shadow .16s ease,border-color .16s ease}
.tcard.avail:hover{transform:translateY(-3px);box-shadow:var(--shadow-h);border-color:var(--navy)}
.tcard .row{display:flex;align-items:flex-start;gap:13px}
.ticon{font-size:26px;line-height:1;width:46px;height:46px;flex:none;display:grid;place-items:center;
  background:var(--surface-2);border:1px solid var(--rule);border-radius:11px}
.tcard h3{margin:0;font-size:19px;font-weight:700;color:var(--navy-text);line-height:1.2;text-wrap:balance}
.tags{display:flex;gap:6px;flex-wrap:wrap;margin-top:8px}
.tag{font-family:"IBM Plex Sans",sans-serif;font-size:11px;font-weight:600;letter-spacing:.03em;
  padding:2px 9px;border-radius:20px;background:var(--blue);color:var(--navy-text)}
.tag.lvl{background:var(--cream);color:#7a5f18}
.tag.soon{background:var(--soon-bg);color:var(--soon)}
.tdesc{margin:14px 0 0;font-size:15px;color:var(--ink-soft);line-height:1.5;flex:1}
.tfoot{display:flex;align-items:center;justify-content:space-between;margin-top:18px;gap:10px}
.meta{font-family:"IBM Plex Sans",sans-serif;font-size:12px;color:var(--ink-faint)}
.open{font-family:"IBM Plex Sans",sans-serif;font-weight:600;font-size:14px;text-decoration:none;
  background:var(--navy-band);color:#fff;padding:8px 15px;border-radius:8px;white-space:nowrap}
.open:hover{filter:brightness(1.12)}
.tcard.soon-card{opacity:.9;border-style:dashed}
.soon-badge{font-family:"IBM Plex Sans",sans-serif;font-weight:600;font-size:13px;color:var(--soon)}
.no-results{max-width:1080px;margin:0 auto;padding:30px 24px;text-align:center;color:var(--ink-faint);font-style:italic}

/* footer */
.foot{background:var(--navy-band);color:#fff;text-align:center;padding:26px 20px;border-top:4px solid var(--gold);margin-top:36px}
.foot .b{font-family:"IBM Plex Sans",sans-serif;font-weight:700;letter-spacing:.1em;font-size:16px}
.foot .s{opacity:.85;font-size:14px;margin-top:3px}
.foot .s a{color:#e9c46a;text-decoration:none}
.tgl{background:transparent;border:1px solid rgba(255,255,255,.4);color:#fff;border-radius:20px;
  padding:5px 11px;font-family:"IBM Plex Sans",sans-serif;font-size:12.5px;cursor:pointer}
.tgl:hover{background:rgba(255,255,255,.12)}
:focus-visible{outline:2px solid var(--gold);outline-offset:2px}

.guide-promo {
  padding: 8px 20px;
  background: #ffd400;
  color: #091a32;
  font: 700 13px/1.25 Arial, sans-serif;
  text-align: center;
}

.guide-promo a { color: #091a32; }

.guide-site-header {
  background: #073665;
  color: #fff;
  border-bottom: 1px solid rgba(255, 255, 255, .45);
}

.guide-site-header__inner {
  max-width: 1280px;
  margin: 0 auto;
  padding: 14px 22px;
  display: flex;
  align-items: center;
  gap: 26px;
}

.guide-site-header__brand {
  flex: 0 0 auto;
  color: #fff;
  font: 700 16px/1.2 Arial, sans-serif;
  text-decoration: none;
  white-space: nowrap;
}

.guide-site-header__brand span { color: #ffd400; }

.guide-site-header__nav {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  flex-wrap: wrap;
  gap: 2px;
  margin-left: auto;
}

.guide-site-header__nav a,
.guide-site-header__nav .tgl {
  color: #fff;
  padding: 8px 9px;
  border-radius: 5px;
  font: 600 12px/1.2 Arial, sans-serif;
  text-decoration: none;
  white-space: nowrap;
}

.guide-site-header__nav a:hover,
.guide-site-header__nav a:focus-visible,
.guide-site-header__nav a.active {
  background: rgba(255, 212, 0, .16);
  color: #ffd400;
}

.guide-site-header__nav .tgl {
  margin-left: 5px;
  border: 1px solid rgba(255,255,255,.5);
  background: transparent;
  cursor: pointer;
}

.guide-site-footer {
  margin-top: 42px;
  padding: 28px 22px;
  background: #073665;
  color: #d8e7f6;
  border-top: 4px solid #ffd400;
  font-family: Arial, sans-serif;
}

.guide-site-footer__inner { max-width: 1280px; margin: 0 auto; }
.guide-site-footer__brand { color: #fff; font-size: 17px; font-weight: 700; }
.guide-site-footer__tagline { margin: 5px 0 16px; font-size: 13px; }
.guide-site-footer__links { display: flex; flex-wrap: wrap; gap: 8px 16px; }
.guide-site-footer__links a { color: #fff; font-size: 12.5px; text-decoration: none; }
.guide-site-footer__links a:hover,
.guide-site-footer__links a:focus-visible { color: #ffd400; text-decoration: underline; }

@media (max-width: 900px) {
  .guide-site-header__inner { align-items: flex-start; flex-direction: column; gap: 10px; }
  .guide-site-header__nav { justify-content: flex-start; margin-left: 0; }
}

@media (max-width: 560px) {
  .guide-site-header__inner { padding: 12px 14px; }
  .guide-site-header__nav { display: grid; grid-template-columns: 1fr 1fr; width: 100%; }
  .guide-site-header__nav a { white-space: normal; }
  .guide-site-header__nav .tgl { grid-column: 1 / -1; margin-left: 0; }
}

@media print {
  .guide-promo,
  .guide-site-header,
  .guide-site-footer { display: none !important; }
}

.learning-guides-nav {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.85rem;
  padding: 0.55rem 1rem;
  background: #f4ead2;
  border-bottom: 1px solid #d7bd7a;
  color: #173b63;
  font: 600 0.88rem/1.35 Arial, sans-serif;
  text-align: center;
}

.learning-guides-nav span {
  color: #6b5430;
  letter-spacing: 0.02em;
}

.learning-guides-nav a {
  color: #174f86;
  text-decoration: none;
}

.learning-guides-nav a:hover,
.learning-guides-nav a:focus-visible {
  color: #0d3154;
  text-decoration: underline;
}

@media (max-width: 640px) {
  .learning-guides-nav {
    flex-wrap: wrap;
    gap: 0.35rem 0.75rem;
  }

  .learning-guides-nav span {
    flex-basis: 100%;
  }
}


.toolbar{position:static;justify-content:flex-end;max-width:1120px;margin:14px auto;padding:0 24px}.toc a{font-size:14px}.toc h4{font-size:14px} .controls-lab{display:grid;grid-template-columns:repeat(auto-fit,minmax(145px,1fr));gap:14px;margin:16px 0}label{display:block;font-family:"IBM Plex Sans",sans-serif;font-size:14px;color:var(--ink-soft)}input,select{box-sizing:border-box;max-width:100%;width:100%;padding:9px;margin-top:6px;background:var(--cream);color:var(--navy-text);border:1px solid var(--rule-strong);border-radius:5px;font:16px "IBM Plex Mono",monospace}button.action,.download{display:inline-block;background:var(--navy-band);color:white;border:0;border-radius:6px;padding:10px 16px;font:14px "IBM Plex Sans",sans-serif;cursor:pointer;text-decoration:none}.result{padding:18px;background:var(--blue);border:1px solid var(--blue-line);border-radius:6px;margin:16px 0}.result strong.big{display:block;font:600 32px "IBM Plex Mono",monospace;color:var(--navy-text)}.formula{background:var(--surface-2);padding:16px;border:1px solid var(--rule);border-radius:6px;font-family:"IBM Plex Mono",monospace;font-size:16px}.error{color:var(--maroon);font-family:"IBM Plex Sans",sans-serif}.qa{border:1px solid var(--rule);border-radius:6px;margin:12px 0;background:var(--surface)}.qa summary{padding:14px 16px;cursor:pointer;color:var(--navy-text);font-weight:600}.qa p{padding:0 16px 14px}.curve-input{min-width:90px;width:100px}.caption,.source-note{font-size:14px;color:var(--ink-soft)}.skip{position:absolute;left:-9999px}.skip:focus{left:12px;top:12px;background:var(--surface);padding:12px;z-index:999}svg text{font-family:"IBM Plex Sans",sans-serif;fill:var(--ink-soft)}.chart{width:100%;height:auto;display:block}.practice-row{margin:18px 0;padding:16px;border:1px solid var(--rule);border-radius:6px}.practice-row input{width:160px;margin-right:10px}.tcard[hidden]{display:none!important} .breadcrumbs{font:14px "IBM Plex Sans",sans-serif;color:var(--ink-soft);margin-bottom:18px}.breadcrumbs a{color:var(--navy-text)}@media print{.toolbar,.guide-site-header,.guide-site-footer,.action,.download,.skip{display:none!important}details>p{display:block!important}.controls-lab{grid-template-columns:repeat(3,1fr)}}

.category-list{max-width:1080px;margin:0 auto;padding:0 24px 50px}.category-list .tcard{padding:30px;max-width:none}.category-list .tcard h2{font-size:clamp(25px,4vw,34px);color:var(--navy-text);margin:0;line-height:1.2}.category-list .tdesc{font-size:18px;max-width:780px;line-height:1.65}.category-list .ticon{flex-shrink:0}.category-list .meta,.category-list .tag{font-size:14px}.category-list .tfoot{flex-wrap:wrap;border-top:1px solid var(--rule);padding-top:20px;gap:16px}.topic-actions{display:flex;gap:12px;flex-wrap:wrap;align-items:center}.topic-actions .open{padding:12px 18px;font-size:15px}.topic-actions .secondary{background:var(--surface);color:var(--navy-text);border:1px solid var(--navy-text)}.category-toolbar{max-width:1080px;margin:0 auto 20px;padding:0 24px;display:flex;justify-content:space-between;gap:16px;align-items:center}.category-toolbar .tgl{background:var(--navy-band)}.category-toolbar p{font:14px "IBM Plex Sans",sans-serif;color:var(--ink-soft)}.topic-coverage{font-size:16px;margin-top:18px;color:var(--ink-soft);max-width:800px;line-height:1.7}.category-breadcrumbs{max-width:1080px;margin:24px auto 0;padding:0 24px;font:14px "IBM Plex Sans",sans-serif;color:var(--ink-soft)}.category-breadcrumbs a{color:var(--navy-text)}.app-launch{display:flex;justify-content:center;margin:24px auto 0;gap:12px;flex-wrap:wrap}.app-launch a{font:600 15px "IBM Plex Sans",sans-serif;text-decoration:none;padding:12px 18px;border-radius:6px;background:var(--navy-band);color:white}.app-launch a.secondary{background:var(--surface);border:1px solid var(--rule-strong);color:var(--navy-text)}@media(max-width:600px){.category-list .tcard{padding:22px}.category-list .row{align-items:flex-start}.category-list .tfoot{align-items:flex-start}.topic-actions{width:100%}.topic-actions .open{white-space:normal}}

.category-list{display:grid;gap:24px}.topic-coverage{margin-bottom:0;padding-left:24px}.topic-coverage li+li{margin-top:8px}

.topic-coverage a{color:var(--navy-text);text-decoration:underline;text-decoration-color:var(--rule-strong);text-underline-offset:4px}.topic-coverage a:hover{color:var(--maroon);text-decoration-color:currentColor}

.article-shell{max-width:1160px;margin:0 auto;padding:32px 24px}.series-nav{font:15px/1.6 "IBM Plex Sans",Arial,sans-serif;display:flex;gap:14px;flex-wrap:wrap;margin:12px 0 28px}.series-nav a,.article-shell a{color:var(--navy-text)}.article-layout{display:grid;grid-template-columns:240px minmax(0,1fr);gap:42px}.article-layout aside{font:15px/1.5 "IBM Plex Sans",Arial,sans-serif;align-self:start;position:sticky;top:16px;max-height:90vh;overflow:auto}.article-layout aside ol{padding-left:22px}.article-layout aside li{margin:12px 0}.article-layout aside a[aria-current=page]{font-weight:700;color:var(--maroon)}.article-content{min-width:0}.article-content section{margin:0 0 42px;scroll-margin-top:20px}.article-content h2{font-size:30px;line-height:1.25;color:var(--navy-text);margin:0 0 16px}.article-content h3{font-size:23px;color:var(--navy-text)}.article-content p,.article-content li{font-size:20px;line-height:1.75}.formula{overflow-x:auto;line-height:1.8;margin:18px 0;font-size:17px}.table-wrap{overflow:auto;margin:20px 0}table{border-collapse:collapse;width:100%;font-size:17px}th,td{text-align:left;padding:14px 16px;border-bottom:1px solid var(--rule);vertical-align:top}th{background:var(--navy-band);color:white;font-family:"IBM Plex Sans",Arial,sans-serif}tr:nth-child(even){background:var(--surface-2)}.qa div{padding:0 18px 18px}.qa div p{margin-bottom:0}.article-content code{overflow-wrap:anywhere;font-size:16px}.series-hero{max-width:1160px;margin:auto;padding:44px 24px 20px}.series-hero h1{font-size:clamp(34px,5vw,56px);color:var(--navy-text);line-height:1.12;max-width:950px;margin:10px 0 20px}.series-hero>p{font-size:22px;max-width:850px;color:var(--ink-soft)}.eyebrow{font:600 13px "IBM Plex Sans",Arial,sans-serif;text-transform:uppercase;letter-spacing:.12em;color:var(--maroon)}.lesson-list{list-style:none;padding:0;counter-reset:lesson}.lesson-list li{border-bottom:1px solid var(--rule);padding:24px 0}.lesson-list h2{margin:0 0 8px}.lesson-list p{margin:0}.lab{padding:24px;border:1px solid var(--rule-strong);background:var(--surface);border-top:4px solid var(--gold)}.lab form{display:flex;flex-wrap:wrap;align-items:end;gap:14px}.lab label{min-width:130px;flex:1}.lab input,.lab select{font-size:16px;background:var(--paper);width:100%}.lab-result{font:600 20px/1.6 "IBM Plex Sans",Arial,sans-serif;color:var(--navy-text);margin:20px 0}.lab-error{color:var(--maroon)}.lab svg{width:100%;height:auto;display:block}.lab .caption{font-size:15px}.nav-end{display:flex;justify-content:space-between;gap:20px;flex-wrap:wrap;border-top:2px solid var(--gold);padding:24px 0}.sources li{font-size:16px}.print-button{border:1px solid var(--rule-strong);padding:8px 12px;background:var(--surface);color:var(--navy-text);font:15px Arial;cursor:pointer}.reading-note{font-size:15px;color:var(--ink-soft)}@media(max-width:850px){.article-layout{grid-template-columns:1fr;gap:25px}.article-layout aside{position:static;max-height:none}.article-layout aside ol{columns:2}.article-content h2{font-size:27px}}@media(max-width:520px){.article-layout aside ol{columns:1}.article-shell{padding:20px 16px}.series-hero{padding:30px 16px 10px}.article-content p,.article-content li{font-size:18px}th,td{padding:11px;font-size:15px}.lab{padding:14px}.lab label{min-width:110px}}@media print{.series-nav,.article-layout aside,.nav-end,.print-button,.lab form,.series-actions{display:none!important}.article-layout{display:block}.article-shell,.series-hero{max-width:none;padding:0}body{background:white!important;color:black!important}.article-content section{break-inside:auto}h2,h3{break-after:avoid}table{font-size:12px}th,td{color:black!important;background:white!important}.formula{white-space:normal;overflow-wrap:anywhere}details>div{display:block!important}.lab{break-inside:avoid}.guide-site-header,.guide-site-footer{display:none!important}}