/* The Hydronic Authority — engineering monograph system */
:root{
  /* paper field */
  --paper:#F6F3EC;
  --paper-2:#EFEAE0;
  --panel:#FCFAF5;

  /* ink */
  --ink:#0F172A;
  --ink-2:#1E293B;
  --slate:#475569;
  --slate-light:#64748B;

  /* dark band */
  --dark:#0F172A;
  --dark-2:#1E293B;
  --line-dark:#334155;
  --dark-text:#CBD5E1;
  --dark-muted:#94A3B8;

  /* hairlines */
  --line:#CBD5E1;
  --line-soft:#DCD6C9;

  /* signature accent */
  --copper:#B87333;
  --copper-hover:#C97F3F;

  /* diagram-only thermal ramp (never UI decoration) */
  --supply:#C2410C;
  --return:#0E7490;

  --link:#9A5F27;
  --link-hover:var(--copper-hover);

  --font-display:"Fraunces",Georgia,"Times New Roman",serif;
  --font-ui:"IBM Plex Sans",-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;
  --font-body:"Source Serif 4",Georgia,"Times New Roman",serif;
  --font-mono:"IBM Plex Mono",ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;

  --maxw:1120px;
  --radius:8px;
  --radius-sm:4px;
  --shadow:0 1px 2px rgba(15,23,42,.05);
  font-size:16px;
  color-scheme:light;
}
*{box-sizing:border-box;margin:0;padding:0}
html{scroll-behavior:smooth}
body{
  font-family:var(--font-ui);
  color:var(--ink);
  background:var(--paper);
  line-height:1.72;
  -webkit-font-smoothing:antialiased;
}
.content p,.content li,.callout p,.lead{font-family:var(--font-body)}
h1,h2,h3,h4{color:var(--ink);font-family:var(--font-display);font-weight:600;line-height:1.22;letter-spacing:-.01em}
h1{font-size:clamp(2rem,4.6vw,2.9rem);font-weight:600}
h2{font-size:clamp(1.35rem,2.4vw,1.55rem);margin-top:2.4rem;margin-bottom:.9rem}
.content>h2{border-top:1px solid var(--line-soft);padding-top:1.5rem}
h3{font-size:1.12rem;margin-top:1.8rem;margin-bottom:.55rem}
p{margin-bottom:1.1rem}
ul,ol{margin:0 0 1.15rem 1.4rem}
li{margin-bottom:.5rem}
a{color:var(--link);text-decoration:underline;text-decoration-thickness:1px;text-decoration-color:color-mix(in srgb,var(--link) 40%,transparent);text-underline-offset:2px}
a:hover{color:var(--link-hover)}
strong{color:var(--ink);font-weight:700}
.wrap{max-width:var(--maxw);margin:0 auto;padding:0 24px}
img{max-width:100%;display:block}
::selection{background:color-mix(in srgb,var(--copper) 25%,var(--paper))}

/* ---- header ---- */
header.site{
  border-bottom:1px solid var(--line);
  background:var(--paper);
  position:sticky;top:0;z-index:50;
}
header.site.scrolled{box-shadow:0 1px 0 var(--line),0 8px 24px -18px rgba(15,23,42,.35)}
header.site .nav{display:flex;align-items:center;justify-content:space-between;min-height:66px;gap:16px;flex-wrap:wrap}
.brand{font-family:var(--font-display);font-weight:600;font-size:1.12rem;color:var(--ink);text-decoration:none;letter-spacing:-.01em;display:flex;align-items:center;gap:.6rem}
.brand:hover{color:var(--ink)}
.brand .mark{display:inline-flex;width:26px;height:26px;border-radius:6px;overflow:hidden;flex:0 0 auto}
.brand .mark svg{display:block;width:26px;height:26px}
.nav-links{display:flex;gap:1.3rem;flex-wrap:wrap;align-items:center}
.nav-links a{font-size:.88rem;font-weight:500;color:var(--slate);text-decoration:none;position:relative;padding:4px 0}
.nav-links a:hover{color:var(--copper)}
.nav-links a::after{content:"";position:absolute;left:0;right:100%;bottom:-2px;height:1px;background:var(--copper);transition:right .2s ease}
.nav-links a:hover::after,.nav-links a.active::after{right:0}
.nav-links a.active{color:var(--copper)}
.nav-links a.cta{
  background:var(--copper);color:#FBF7EF;padding:.45rem .95rem;border-radius:6px;
  border:1px solid var(--copper);font-weight:600;
}
.nav-links a.cta::after{display:none}
.nav-links a.cta:hover{color:#FBF7EF;background:var(--copper-hover);border-color:var(--copper-hover)}

/* ---- page head (dark hero band, 2% blueprint grid) ---- */
.page-head{
  background-color:var(--dark);
  background-image:
    linear-gradient(color-mix(in srgb,var(--dark-text) 5%,transparent) 1px,transparent 1px),
    linear-gradient(90deg,color-mix(in srgb,var(--dark-text) 5%,transparent) 1px,transparent 1px);
  background-size:34px 34px;
  border-bottom:1px solid var(--line-dark);
  padding:64px 0;position:relative;
}
.page-head h1{color:#F4EFE6;max-width:22ch}
.page-head .kicker{
  font-family:var(--font-mono);font-size:.74rem;font-weight:500;letter-spacing:.16em;text-transform:uppercase;
  color:var(--copper-hover);margin-bottom:.8rem;display:block;
}
.page-head p.lead{font-size:1.12rem;color:var(--dark-text);max-width:64ch;margin-top:1rem}
.page-head a{color:var(--copper-hover)}
.page-head a.btn{color:#FBF7EF;text-decoration:none}

/* ---- homepage hero layout ---- */
.hero{display:grid;grid-template-columns:1.05fr 1fr;gap:44px;align-items:center}
.hero-art{position:relative}
.hero-art svg{width:100%;height:auto;display:block;border:1px solid var(--line-dark);border-radius:var(--radius);background:var(--dark-2)}
.hero-art figcaption,.figcap{
  margin-top:10px;font-family:var(--font-mono);font-size:.76rem;letter-spacing:.02em;
  color:var(--dark-muted);
}
@media(max-width:880px){.hero{grid-template-columns:1fr;gap:28px}.hero-art{order:2}}

/* ---- content ---- */
main{padding:52px 0 68px}
.content{max-width:74ch}
.content.wide{max-width:var(--maxw)}
.content p{color:var(--ink-2)}

/* ---- editorial index (homepage) ---- */
.idx-intro{max-width:74ch}
.tool-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(272px,1fr));gap:16px;margin:1.6rem 0 2.4rem}
.tool{
  border:1px solid var(--line);border-radius:var(--radius);padding:22px 24px;background:var(--panel);
  text-decoration:none;display:block;transition:border-color .18s,box-shadow .18s;
}
.tool:hover{border-color:var(--copper);box-shadow:var(--shadow)}
.tool .t-tag{font-family:var(--font-mono);font-size:.68rem;font-weight:500;letter-spacing:.14em;text-transform:uppercase;color:var(--copper);display:block;margin-bottom:10px}
.tool h3{margin:0 0 6px;font-size:1.06rem;color:var(--ink)}
.tool p{font-size:.92rem;color:var(--slate);margin-bottom:0;font-family:var(--font-body)}
.tool .t-go{font-family:var(--font-mono);font-size:.76rem;color:var(--copper);display:block;margin-top:12px}

.idx-group{margin:2.2rem 0}
.idx-group-h{
  font-family:var(--font-mono);font-size:.74rem;font-weight:500;letter-spacing:.14em;text-transform:uppercase;
  color:var(--copper);border-bottom:1px solid var(--line);padding-bottom:.5rem;margin-bottom:.2rem;
  display:flex;justify-content:space-between;align-items:baseline;gap:1rem;
}
.idx-group-h .count{color:var(--slate-light);letter-spacing:.04em;text-transform:none}
a.guide-row{
  display:grid;grid-template-columns:2.6rem minmax(160px,240px) 1fr;gap:6px 20px;align-items:baseline;
  padding:11px 0;border-bottom:1px solid var(--line-soft);text-decoration:none;
}
a.guide-row:hover{background:color-mix(in srgb,var(--copper) 5%,transparent)}
a.guide-row .n{font-family:var(--font-mono);font-size:.78rem;color:var(--slate-light)}
a.guide-row .t{font-family:var(--font-ui);font-weight:600;font-size:.95rem;color:var(--ink)}
a.guide-row:hover .t{color:var(--copper)}
a.guide-row .d{font-family:var(--font-body);font-size:.9rem;color:var(--slate)}
@media(max-width:640px){
  a.guide-row{grid-template-columns:2rem 1fr}
  a.guide-row .d{grid-column:2}
}

/* ---- cards (legacy grid, retained for any page still using it) ---- */
.card-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(258px,1fr));gap:16px;margin:1.8rem 0 2.2rem}
.card{
  border:1px solid var(--line);border-radius:var(--radius);padding:22px;background:var(--panel);
  text-decoration:none;display:block;transition:border-color .18s,box-shadow .18s;
}
.card:hover{border-color:var(--copper);box-shadow:var(--shadow)}
.card .ico{width:38px;height:38px;border-radius:6px;border:1px solid var(--line);display:flex;align-items:center;justify-content:center;margin-bottom:12px}
.card .ico svg{width:22px;height:22px;stroke:var(--copper);fill:none;stroke-width:1.8}
.card h3{margin-top:0;font-size:1.05rem;color:var(--ink)}
.card p{font-size:.92rem;color:var(--slate);margin-bottom:0}
.card .tag{display:inline-block;font-family:var(--font-mono);font-size:.66rem;font-weight:500;letter-spacing:.12em;text-transform:uppercase;color:var(--copper);margin-bottom:8px}

/* ---- callout boxes ---- */
.callout{background:var(--paper-2);border:1px solid var(--line-soft);border-left:3px solid var(--copper);border-radius:var(--radius-sm);padding:20px 24px;margin:1.8rem 0}
.callout h4{margin:0 0 .4rem;font-size:1rem;color:var(--ink)}
.callout p{margin-bottom:0;font-size:.96rem;color:var(--slate)}
.callout.installer{border-left-color:var(--copper)}

/* ---- pull quotes ---- */
.pullquote{
  font-family:var(--font-display);font-style:italic;font-size:1.25rem;line-height:1.5;color:var(--ink);
  border-left:3px solid var(--copper);padding:6px 0 6px 22px;margin:2rem 0;
}

/* ---- figures / SVG diagrams ---- */
.figure{margin:2rem 0;padding:26px;background:var(--panel);border:1px solid var(--line);border-radius:var(--radius)}
.figure svg{width:100%;height:auto;display:block}
.figure figcaption{
  margin-top:14px;padding-top:12px;border-top:1px solid var(--line-soft);
  font-family:var(--font-mono);font-size:.78rem;color:var(--slate-light);text-align:left;letter-spacing:.01em;
}
.diagram text{font-family:var(--font-mono)}

/* ---- tables (spec tables — mono data) ---- */
table{
  width:100%;border-collapse:collapse;margin:1.6rem 0;font-size:.88rem;
  background:var(--panel);border:1px solid var(--line);
  font-family:var(--font-mono);
}
caption{caption-side:top;text-align:left;font-family:var(--font-mono);font-size:.76rem;color:var(--slate-light);padding-bottom:8px;letter-spacing:.02em}
th,td{padding:11px 14px;text-align:left;vertical-align:top;border-bottom:1px solid var(--line-soft)}
tr:last-child td{border-bottom:none}
th{
  background:var(--paper-2);font-family:var(--font-ui);font-weight:600;color:var(--ink);
  font-size:.78rem;letter-spacing:.04em;border-bottom:1px solid var(--line);
}
td:first-child{font-family:var(--font-ui);font-weight:600;color:var(--ink);font-size:.86rem}
tbody tr:hover td,table tr:hover td{background:color-mix(in srgb,var(--copper) 5%,transparent)}

/* ---- comparison bars ---- */
.compare{margin:2rem 0;display:grid;gap:16px}
.cmp-row{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius);padding:18px 20px}
.cmp-row h4{font-size:.95rem;margin:0 0 4px}
.cmp-row .metric-note{font-family:var(--font-mono);font-size:.74rem;color:var(--slate-light);margin-bottom:14px}
.cmp-bar{display:grid;grid-template-columns:130px 1fr;gap:12px;align-items:center;margin-bottom:10px}
.cmp-bar:last-child{margin-bottom:0}
.cmp-bar .lbl{font-size:.85rem;font-weight:600;color:var(--slate)}
.cmp-bar .track{background:var(--paper-2);border:1px solid var(--line-soft);border-radius:var(--radius-sm);height:24px;position:relative;overflow:hidden}
.cmp-bar .fill{
  height:100%;width:0;transition:width 1.1s cubic-bezier(.2,.8,.2,1);
  display:flex;align-items:center;justify-content:flex-end;padding-right:10px;
  font-family:var(--font-mono);font-size:.74rem;font-weight:500;color:#FBF7EF;
}
.cmp-bar .fill.boiler{background:var(--ink-2)}
.cmp-bar .fill.hp{background:var(--copper)}
.reveal .cmp-bar .fill[data-w]{width:var(--w)}
.cmp-legend{display:flex;gap:18px;flex-wrap:wrap;font-size:.84rem;font-weight:500;color:var(--slate);margin:.4rem 0 1.4rem}
.cmp-legend span{display:inline-flex;align-items:center;gap:.45rem}
.cmp-legend i{width:12px;height:12px;border-radius:3px;display:inline-block}
.cmp-legend i.boiler{background:var(--ink-2)}
.cmp-legend i.hp{background:var(--copper)}

/* ---- faq ---- */
.faq details{border:1px solid var(--line);border-radius:var(--radius-sm);padding:6px 20px;margin-bottom:10px;background:var(--panel);transition:border-color .18s}
.faq details[open]{border-color:var(--copper)}
.faq summary{font-weight:600;cursor:pointer;color:var(--ink);padding:12px 0;list-style:none;display:flex;justify-content:space-between;align-items:center;gap:1rem}
.faq summary::-webkit-details-marker{display:none}
.faq summary::after{content:"+";font-family:var(--font-mono);font-size:1.2rem;color:var(--copper);transition:transform .2s;line-height:1}
.faq details[open] summary::after{transform:rotate(45deg)}
.faq details p{margin-top:.2rem;margin-bottom:.9rem;color:var(--slate)}

/* ---- glossary ---- */
dl.glossary dt{font-weight:600;color:var(--ink);margin-top:1.5rem;font-size:1.04rem;font-family:var(--font-display)}
dl.glossary dt::before{content:"";display:inline-block;width:8px;height:8px;border-radius:2px;background:var(--copper);margin-right:.55rem;vertical-align:middle}
dl.glossary dd{margin-left:0;color:var(--slate);margin-bottom:.3rem}

/* ---- table of contents ---- */
.toc{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius-sm);padding:16px 20px;margin:1.6rem 0;font-size:.9rem}
.toc h4{margin:0 0 .5rem;font-family:var(--font-mono);font-size:.72rem;font-weight:500;letter-spacing:.14em;text-transform:uppercase;color:var(--copper)}
.toc ul{margin:0;list-style:none}
.toc li{margin-bottom:.3rem}
.toc a{color:var(--slate);text-decoration:none}
.toc a:hover{color:var(--copper)}
/* long guide pages: sticky rail TOC beside the article */
.has-toc{display:grid;grid-template-columns:220px minmax(0,1fr);gap:44px;max-width:var(--maxw)}
.has-toc .toc{align-self:start;position:sticky;top:96px;margin:0}
.has-toc .article{max-width:74ch;min-width:0}
@media(max-width:880px){
  .has-toc{display:block}
  .has-toc .toc{position:static;margin:1.6rem 0}
}

/* ---- buttons ---- */
.btn{
  display:inline-flex;align-items:center;gap:.5rem;background:var(--copper);color:#FBF7EF;
  padding:.7rem 1.35rem;border-radius:6px;font-weight:600;font-size:.92rem;font-family:var(--font-ui);
  text-decoration:none;border:1px solid var(--copper);cursor:pointer;transition:background .15s,border-color .15s;
}
.btn:hover{color:#FBF7EF;background:var(--copper-hover);border-color:var(--copper-hover)}
.btn.outline{background:transparent;color:var(--copper-hover);border:1px solid var(--line-dark)}
.page-head .btn.outline{color:#E8DFD2;border-color:var(--line-dark)}
.btn.outline:hover{background:transparent;border-color:var(--copper-hover);color:var(--copper-hover)}
.content .btn.outline{color:var(--copper);border-color:var(--copper)}
.content .btn.outline:hover{color:var(--copper-hover);border-color:var(--copper-hover)}
.btn-row{display:flex;flex-wrap:wrap;align-items:center;gap:14px;margin-top:1.4rem}
@media(max-width:480px){.btn-row{gap:12px}.btn-row .btn{width:100%;justify-content:center}}

/* ---- calculator ---- */
.calc{display:grid;grid-template-columns:.95fr 1.1fr;gap:24px;margin:2rem 0;align-items:start}
@media(max-width:820px){.calc{grid-template-columns:1fr}}
.calc-panel{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius);padding:26px}
.calc-panel h3{margin-top:0}
.field{margin-bottom:18px}
.field label{display:block;font-size:.86rem;font-weight:600;color:var(--ink);margin-bottom:7px}
.field .val{float:right;color:var(--copper);font-family:var(--font-mono);font-weight:500;font-size:.84rem}
.field input[type=range]{width:100%;accent-color:var(--copper);height:6px}
.field select{width:100%;padding:11px 12px;border:1px solid var(--line);border-radius:var(--radius-sm);background:var(--paper);color:var(--ink);font-size:.92rem;font-family:var(--font-ui)}
.field select:focus{outline:2px solid var(--copper);outline-offset:1px}
.result h3{margin-top:0}
.stat{display:flex;align-items:baseline;gap:.6rem;background:var(--paper-2);border:1px solid var(--line-soft);border-radius:var(--radius-sm);padding:18px 22px;margin-bottom:20px}
.stat .num{font-family:var(--font-mono);font-size:2.3rem;font-weight:600;letter-spacing:-.02em;color:var(--copper)}
.stat .unit{font-family:var(--font-mono);font-weight:500;font-size:.9rem;color:var(--slate)}
.cost-bar{margin-bottom:14px}
.cost-bar .top{display:flex;justify-content:space-between;font-size:.86rem;font-weight:600;margin-bottom:6px}
.cost-bar .top span:last-child{font-family:var(--font-mono);font-weight:500}
.cost-bar .track{background:var(--paper-2);border:1px solid var(--line-soft);border-radius:var(--radius-sm);height:28px;overflow:hidden}
.cost-bar .fill{
  height:100%;transition:width .7s cubic-bezier(.2,.8,.2,1);
  display:flex;align-items:center;justify-content:flex-end;padding-right:12px;
  color:#FBF7EF;font-family:var(--font-mono);font-weight:500;font-size:.76rem;white-space:nowrap;
}
.cost-bar .fill.radiant{background:var(--copper)}
.cost-bar .fill.forced{background:var(--slate-light)}
.assump{font-size:.8rem;color:var(--slate-light);margin-top:20px;border-top:1px dashed var(--line);padding-top:14px;font-family:var(--font-mono)}
.assump strong{color:var(--slate)}

/* ---- savings callout (calculator) ---- */
.savings-hero{margin-top:1.4rem;padding:1.2rem 1.4rem;border-radius:var(--radius-sm);text-align:center;background:var(--paper-2);border:1px solid var(--line-soft);border-top:3px solid var(--copper)}
.savings-hero .save-label{display:block;font-family:var(--font-mono);font-size:.72rem;letter-spacing:.12em;text-transform:uppercase;color:var(--slate)}
.savings-hero .save-num{display:block;font-family:var(--font-mono);font-size:2.4rem;font-weight:600;line-height:1.1;margin:.2rem 0;color:var(--copper)}
.savings-hero .save-sub{display:block;font-size:.88rem;color:var(--slate);font-family:var(--font-body)}

/* ---- geo-aware installer banner ---- */
.geo-banner{margin-top:1.4rem;padding:.9rem 1.15rem;border-radius:var(--radius-sm);font-size:.95rem;line-height:1.5}
.geo-banner.is-utah{background:var(--paper-2);border:1px solid var(--copper);color:var(--ink-2)}
.geo-banner.is-other{background:var(--paper-2);border:1px solid var(--line-soft);color:var(--slate)}
.geo-note{margin:.25rem 0 1rem;font-size:.9rem;color:var(--slate-light);font-style:italic}
.callout.installer.deemphasized{opacity:.65}

/* ---- keep-reading row (JS-injected) ---- */
.related{margin-top:2.6rem;border-top:1px solid var(--line);padding-top:1.2rem}
.related .kicker{font-family:var(--font-mono);font-size:.72rem;font-weight:500;letter-spacing:.14em;text-transform:uppercase;color:var(--copper);display:block;margin-bottom:.7rem}
.related-grid{display:flex;flex-wrap:wrap;gap:8px 26px}
.related-grid a{font-size:.9rem;font-weight:500;color:var(--slate);text-decoration:none;border-bottom:1px solid var(--line)}
.related-grid a:hover{color:var(--copper);border-bottom-color:var(--copper)}

/* ---- footer ---- */
footer.site{background:var(--dark);color:var(--dark-muted);padding:52px 0 30px;margin-top:52px;border-top:1px solid var(--line-dark)}
footer.site .wrap{display:flex;flex-direction:column;gap:14px}
footer.site a{color:var(--dark-text);text-decoration:none}
footer.site a:hover{color:#fff}
footer.site .foot-links{display:flex;gap:1.4rem;flex-wrap:wrap;font-size:.9rem;font-weight:500}
footer.site .tagline{font-size:.9rem;color:var(--dark-muted);max-width:60ch}
footer.site .copyright{font-size:.8rem;color:#64748B;font-family:var(--font-mono)}
.foot-brand .fb-mark{display:flex;align-items:center;gap:.6rem;font-family:var(--font-display);font-weight:600;font-size:1.05rem;color:#F4EFE6;margin-bottom:8px}
.foot-brand .mark{display:inline-flex;width:24px;height:24px;border-radius:6px;overflow:hidden}
.foot-brand .mark svg{display:block;width:24px;height:24px}
.foot-h{font-family:var(--font-mono);font-size:.7rem;font-weight:500;letter-spacing:.14em;text-transform:uppercase;color:var(--copper-hover);margin-bottom:6px}

/* ---- scroll reveal ---- */
.reveal{opacity:0;transform:translateY(16px);transition:opacity .6s ease,transform .6s cubic-bezier(.2,.7,.2,1)}
.reveal.in{opacity:1;transform:none}

@media(max-width:720px){
  .nav-links{gap:1rem;font-size:.84rem;width:100%;justify-content:flex-start;order:3}
  .nav-links a{padding:2px 0}
  header.site .nav{padding:12px 0}
  .page-head{padding:44px 0}
}
@media(prefers-reduced-motion:reduce){
  *{scroll-behavior:auto!important}
  .reveal{opacity:1!important;transform:none!important;transition:none!important}
  .cmp-bar .fill,.cost-bar .fill{transition:none}
}

/* ---- diagram flow animation (per-path direction; motion-safe only) ---- */
@media (prefers-reduced-motion: no-preference){
  @keyframes flowFwd{to{stroke-dashoffset:-96}}
  @keyframes flowRev{to{stroke-dashoffset:96}}
  .flow-path{stroke-dasharray:2 10;stroke-linecap:round;animation:flowFwd 2.6s linear infinite}
  .flow-path.rev{animation-name:flowRev}
}

/* ---- article metadata byline ---- */
.byline{
  font-family:var(--font-mono);
  font-size:.76rem;
  color:var(--dark-muted);
  margin-top:1.1rem;
  padding-top:.75rem;
  border-top:1px solid var(--line-dark);
  display:flex;
  flex-wrap:wrap;
  gap:6px 16px;
  align-items:center;
}
.byline span{display:inline-flex;align-items:center}