:root{
  --bg:#F5F7F7; --surface:#FFFFFF; --ink:#1C2427; --muted:#5C696C; --line:#DDE3E4;
  --accent:#146C6A; --accent-ink:#FFFFFF; --accent-soft:#E2EFEE; --warn:#9A5B00;
  --side:236px; --top:56px;
}
@media (prefers-color-scheme: dark){
  :root{ --bg:#121819; --surface:#1A2224; --ink:#E6ECEC; --muted:#9AA8AA; --line:#2C3739;
    --accent:#5FBDB8; --accent-ink:#0E1415; --accent-soft:#1F3534; --warn:#F2B25C; }
}
*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%;height:100%}
body{margin:0;min-height:100%;background:var(--bg);color:var(--ink);
  font-family:"IBM Plex Sans",system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;font-size:1rem;line-height:1.55;
  padding-bottom:env(safe-area-inset-bottom,0px)}
a{color:var(--accent)}
:focus-visible{outline:2px solid var(--accent);outline-offset:2px}
h1{font-size:1.6rem;line-height:1.2;margin:0 0 .35rem;font-weight:600;letter-spacing:-.01em}
h2{font-size:1.1rem;margin:1.8rem 0 .4rem;font-weight:600}
p{margin:.4rem 0}

/* top bar */
.topbar{position:sticky;top:0;z-index:20;background:var(--surface);border-bottom:1px solid var(--line);
  padding-top:env(safe-area-inset-top,0px)}
.topbar-in{height:var(--top);display:flex;align-items:center;justify-content:space-between;gap:1rem;padding:0 1rem}
.brand{font-weight:600;font-size:1.1rem;color:var(--ink);text-decoration:none;display:flex;align-items:center;gap:.5rem}
.brand svg{width:22px;height:22px;flex:none}

/* layout */
.shell{display:grid;grid-template-columns:var(--side) minmax(0,1fr);min-height:calc(100vh - var(--top))}
.sidebar{border-right:1px solid var(--line);background:var(--surface);padding:1rem .75rem 2rem;
  position:sticky;top:calc(var(--top) + env(safe-area-inset-top,0px));height:calc(100vh - var(--top) - env(safe-area-inset-top,0px));overflow-y:auto}
.sidebar h3{font-size:.8rem;font-weight:600;color:var(--muted);margin:1rem .6rem .35rem}
.sidebar h3:first-child{margin-top:0}
.sidebar ul{list-style:none;margin:0;padding:0}
.sidebar a{display:block;padding:.45rem .6rem;border-radius:6px;color:var(--ink);text-decoration:none;font-size:.95rem}
.sidebar a:hover{background:var(--bg)}
.sidebar a[aria-current="page"]{background:var(--accent-soft);color:var(--accent);font-weight:600}
.sidebar .meta{margin-top:1.5rem;padding:0 .6rem;font-size:.85rem}
.sidebar .meta a{display:inline-block;white-space:nowrap;padding:0;color:var(--muted);margin-right:.75rem}
.content{padding:1.75rem 2rem 3rem;max-width:880px;width:100%}
.lede{color:var(--muted);max-width:62ch;margin-bottom:1.25rem}

/* calculator area */
.calc{background:var(--surface);border:1px solid var(--line);border-radius:10px;display:grid;grid-template-columns:minmax(0,1fr) minmax(0,.85fr)}
.fields{padding:1.25rem;display:grid;gap:.9rem;align-content:start}
.row{display:grid;grid-template-columns:1fr 1fr;gap:.75rem}
label{display:block;font-size:.88rem;font-weight:600;margin-bottom:.3rem}
input,select{width:100%;font:inherit;padding:.55rem .65rem;border:1px solid var(--line);border-radius:6px;background:var(--surface);color:var(--ink)}
input:focus,select:focus{border-color:var(--accent)}
.hint{font-size:.82rem;color:var(--muted);margin:.3rem 0 0}
.seg{display:flex;border:1px solid var(--line);border-radius:6px;overflow:hidden;background:var(--surface)}
.seg button{flex:1;font:inherit;font-size:.9rem;padding:.45rem .5rem;border:0;background:transparent;color:var(--muted);cursor:pointer}
.seg button+button{border-left:1px solid var(--line)}
.seg button[aria-pressed="true"]{background:var(--accent);color:var(--accent-ink);font-weight:600}
.seg.sys button{flex:none;padding:.35rem .8rem}
.btn{font:inherit;font-weight:600;padding:.55rem 1rem;border:0;border-radius:6px;background:var(--accent);color:var(--accent-ink);cursor:pointer;justify-self:start}

.result{border-left:1px solid var(--line);background:var(--bg);padding:1.25rem;border-radius:0 10px 10px 0;display:flex;flex-direction:column;gap:.35rem}
.result .label{font-size:.82rem;font-weight:600;color:var(--muted)}
.big{font-size:2.2rem;font-weight:600;line-height:1.1;font-variant-numeric:tabular-nums}
.sub{font-weight:600}
.notes{font-size:.9rem;color:var(--muted)}
.meter{height:6px;border-radius:3px;background:var(--line);overflow:hidden;margin:.4rem 0 .2rem}
.meter .water{height:100%;width:0;background:var(--accent);transition:width .3s ease}
@media (prefers-reduced-motion:reduce){.meter .water{transition:none}}
.warn{color:var(--warn);font-weight:600}
.stock{list-style:none;padding:0;margin:0;display:grid;gap:.35rem}
.stock li{display:flex;justify-content:space-between;align-items:center;gap:.5rem;padding:.4rem .6rem;border:1px solid var(--line);border-radius:6px;font-size:.92rem}
.stock button{font:inherit;font-size:.85rem;border:0;background:transparent;color:var(--muted);cursor:pointer;text-decoration:underline}

.guide{max-width:68ch;margin-top:.5rem}
.faq dt{font-weight:600;margin-top:1rem}
.faq dd{margin:.2rem 0 0;color:var(--ink)}
.ad-slot{margin:2rem 0}

/* home */
.home-group{margin-top:1.5rem}
.home-group h2{font-size:.95rem;color:var(--muted);margin:0 0 .5rem}
.tiles{list-style:none;padding:0;margin:0;display:grid;grid-template-columns:repeat(auto-fill,minmax(230px,1fr));gap:.6rem}
.tiles a{display:block;height:100%;padding:.85rem 1rem;background:var(--surface);border:1px solid var(--line);border-radius:8px;text-decoration:none;color:var(--ink)}
.tiles a:hover{border-color:var(--accent)}
.tiles strong{display:block;font-weight:600}
.tiles span{display:block;font-size:.88rem;color:var(--muted);margin-top:.15rem}

footer{border-top:1px solid var(--line);margin-top:2.5rem;padding-top:1rem;font-size:.85rem;color:var(--muted)}
footer a{color:var(--muted);margin-right:1rem}

/* phones and small tablets: sidebar becomes a scrollable tool strip */
@media (max-width:820px){
  .shell{display:block}
  .sidebar{position:sticky;top:calc(var(--top) + env(safe-area-inset-top,0px));z-index:15;height:auto;border-right:0;border-bottom:1px solid var(--line);
    padding:.5rem .75rem;overflow-x:auto;overflow-y:hidden;white-space:nowrap;-webkit-overflow-scrolling:touch}
  .sidebar h3,.sidebar .meta{display:none}
  .sidebar nav{display:flex;gap:.25rem}
  .sidebar ul{display:flex;gap:.25rem}
  .sidebar a{padding:.4rem .75rem;border:1px solid var(--line);border-radius:999px;font-size:.9rem}
  .sidebar a[aria-current="page"]{border-color:var(--accent)}
  .content{padding:1.25rem 1rem 2.5rem}
  .calc{grid-template-columns:1fr}
  .result{border-left:0;border-top:1px solid var(--line);border-radius:0 0 10px 10px}
}
@media (max-width:420px){.seg.sys button{padding:.3rem .55rem;font-size:.85rem}}
.table-wrap{overflow-x:auto;margin:.5rem 0}
table.facts{width:100%;border-collapse:separate;border-spacing:0;background:var(--surface);border:1px solid var(--line);border-radius:10px;overflow:hidden;font-variant-numeric:tabular-nums}
.facts th,.facts td{text-align:left;padding:.6rem .85rem;border-bottom:1px solid var(--line);vertical-align:top}
.facts tr:last-child th,.facts tr:last-child td{border-bottom:0}
.facts th[scope="row"]{font-weight:600;width:52%}
.facts thead th{font-size:.85rem;color:var(--muted);background:var(--bg)}
.facts td span{color:var(--muted);font-size:.9rem}
.chart th[scope="row"]{width:auto}
.related-links{padding-left:1.1rem}
.related-links li{margin:.25rem 0}
.chips{list-style:none;padding:0;display:flex;flex-wrap:wrap;gap:.4rem}
.chips a{display:inline-block;padding:.35rem .75rem;border:1px solid var(--line);border-radius:999px;text-decoration:none;color:var(--ink);background:var(--surface);font-size:.9rem}
.chips a[aria-current="page"]{border-color:var(--accent);color:var(--accent);font-weight:600}