/* SciSpark Sheets — periodic-table-inspired editorial design.
   Subject color coding:
     Life Science     → green  (#16a34a)
     Earth Science    → blue   (#1d4ed8)
     Physical Science → orange (#ea580c)
*/
:root{
  --ink:#0b1220;
  --ink-2:#1f2937;
  --muted:#5b6472;
  --line:#e5e7eb;
  --line-2:#eef0f3;
  --bg:#f7f7f4;          /* paper-like background */
  --paper:#ffffff;
  --grid:rgba(15,23,42,.04);
  --brand:#0f172a;
  --accent:#f59e0b;
  --life:#16a34a;        --life-50:#ecfdf5; --life-200:#bbf7d0; --life-700:#15803d;
  --earth:#1d4ed8;       --earth-50:#eff6ff; --earth-200:#bfdbfe; --earth-700:#1e40af;
  --phys:#ea580c;        --phys-50:#fff7ed; --phys-200:#fed7aa; --phys-700:#c2410c;
  --shadow:0 1px 0 rgba(15,23,42,.04), 0 8px 24px rgba(15,23,42,.06);
  --shadow-lg:0 1px 0 rgba(15,23,42,.04), 0 24px 60px rgba(15,23,42,.08);
  --r:14px; --r-sm:10px; --r-lg:22px;
  --maxw:1200px;
  --mono:"JetBrains Mono","SF Mono",ui-monospace,Menlo,Consolas,monospace;
  --sans:"Inter",ui-sans-serif,system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;
  --serif:"Source Serif Pro",ui-serif,Georgia,"Times New Roman",serif;
}
*{box-sizing:border-box}
html,body{margin:0;padding:0}
body{
  font-family:var(--sans);
  color:var(--ink);
  background:
    radial-gradient(circle at 1px 1px, var(--grid) 1px, transparent 0) 0 0/24px 24px,
    var(--bg);
  line-height:1.6;
  font-feature-settings:"ss01","ss02";
  -webkit-font-smoothing:antialiased;
}
img{max-width:100%;height:auto;display:block}
a{color:var(--earth-700);text-decoration:none}
a:hover{text-decoration:underline;text-underline-offset:3px}
.wrap{max-width:var(--maxw);margin:0 auto;padding:0 28px}
.muted{color:var(--muted)}
.small{font-size:.875rem}

/* ---------- Header ---------- */
.site-header{
  background:rgba(255,255,255,.92);
  backdrop-filter:saturate(160%) blur(8px);
  border-bottom:1px solid var(--line);
  position:sticky;top:0;z-index:20;
}
.header-row{display:flex;align-items:center;justify-content:space-between;gap:24px;padding:14px 28px}
.brand{display:inline-flex;align-items:center;gap:12px;font-weight:700;color:var(--ink);font-size:1.1rem;letter-spacing:-.01em}
.brand:hover{text-decoration:none}
.brand-mark{
  display:inline-grid;place-items:center;width:36px;height:36px;border-radius:8px;
  background:#0b1220;color:#fff;font-family:var(--mono);font-weight:700;font-size:.9rem;
  position:relative;line-height:1;
}
.brand-mark::before{
  content:"118";position:absolute;top:3px;right:5px;font-size:.5rem;color:#fcd34d;
}
.brand-name{font-weight:800}
.brand-name em{font-style:normal;color:var(--accent)}

.primary-nav{display:flex;flex-wrap:wrap;gap:4px;align-items:center;font-weight:500;font-size:.95rem}
.primary-nav a{color:var(--ink-2);padding:8px 12px;border-radius:8px;transition:background .15s}
.primary-nav a:hover{background:#f1f5f9;text-decoration:none}
.primary-nav a.life:hover{background:var(--life-50);color:var(--life-700)}
.primary-nav a.earth:hover{background:var(--earth-50);color:var(--earth-700)}
.primary-nav a.phys:hover{background:var(--phys-50);color:var(--phys-700)}

/* ---------- Breadcrumb ---------- */
.crumbs{padding:18px 28px 0}
.crumbs ol{list-style:none;padding:0;margin:0;display:flex;flex-wrap:wrap;gap:6px;font-size:.85rem;color:var(--muted);font-family:var(--mono)}
.crumbs a{color:var(--muted)}
.crumbs a:hover{color:var(--ink)}
.crumbs [aria-current]{color:var(--ink)}

/* ---------- Main ---------- */
.site-main{padding:28px 28px 64px}
h1,h2,h3,h4{line-height:1.15;color:var(--ink);margin:0 0 .5em;letter-spacing:-.015em}
h1{font-size:clamp(2rem, 1.4rem + 2.4vw, 3rem);font-weight:800}
h2{font-size:1.65rem;margin-top:1.6em;font-weight:700}
h3{font-size:1.15rem;font-weight:700}
h4{font-size:.95rem;font-weight:700;text-transform:uppercase;letter-spacing:.06em;color:var(--muted)}
p{margin:0 0 1em}

/* ---------- Hero ---------- */
.hero{
  display:grid;grid-template-columns:1.1fr .9fr;gap:36px;align-items:center;
  background:linear-gradient(180deg,#ffffff,#fbfaf2);
  border:1px solid var(--line);border-radius:var(--r-lg);
  padding:48px;box-shadow:var(--shadow-lg);
  margin-bottom:36px;position:relative;overflow:hidden;
}
.hero::before{
  content:"";position:absolute;inset:auto -80px -80px auto;width:300px;height:300px;
  background:radial-gradient(closest-side,rgba(245,158,11,.18),transparent);
  pointer-events:none;
}
.hero .eyebrow{
  display:inline-flex;align-items:center;gap:8px;
  font-family:var(--mono);font-size:.78rem;text-transform:uppercase;letter-spacing:.12em;
  color:var(--earth-700);background:var(--earth-50);
  padding:6px 10px;border-radius:999px;border:1px solid var(--earth-200);
  margin-bottom:14px;
}
.hero .eyebrow .dot{width:6px;height:6px;border-radius:50%;background:var(--life)}
.hero h1{font-size:clamp(2.2rem, 1.4rem + 2.8vw, 3.4rem);margin-bottom:.4em}
.hero h1 mark{background:linear-gradient(180deg,transparent 60%,#fde68a 60%);color:inherit;padding:0 .1em}
.hero p.lede{font-size:1.15rem;color:var(--ink-2);max-width:54ch}
.hero .cta{display:inline-flex;flex-wrap:wrap;gap:10px;margin-top:18px}
.btn{display:inline-flex;align-items:center;gap:8px;padding:12px 18px;border-radius:10px;font-weight:600;font-size:.95rem;border:1px solid transparent;transition:transform .12s, box-shadow .12s, background .12s}
.btn:hover{text-decoration:none;transform:translateY(-1px)}
.btn-primary{background:var(--ink);color:#fff;box-shadow:0 8px 24px rgba(15,23,42,.18)}
.btn-primary:hover{background:#000}
.btn-ghost{background:#fff;border-color:var(--line);color:var(--ink)}
.btn-ghost:hover{background:#f8fafc}
.hero-img{
  border-radius:18px;overflow:hidden;border:1px solid var(--line);background:#fff;
  box-shadow:var(--shadow);position:relative;
}
@media (max-width:880px){.hero{grid-template-columns:1fr;padding:32px}.hero h1{font-size:2.1rem}}

/* ---------- KPI strip ---------- */
.kpi-row{display:flex;flex-wrap:wrap;gap:10px;margin:18px 0 6px}
.kpi{
  background:#fff;border:1px solid var(--line);border-radius:10px;padding:8px 12px;
  font-family:var(--mono);font-size:.82rem;color:var(--muted);
}
.kpi b{color:var(--ink);font-weight:700}

/* ---------- Subject section header ---------- */
.section-head{display:flex;align-items:end;justify-content:space-between;gap:16px;margin:48px 0 16px;border-bottom:1px solid var(--line);padding-bottom:10px}
.section-head h2{margin:0;font-size:1.3rem}
.section-head .meta{font-family:var(--mono);font-size:.78rem;color:var(--muted);text-transform:uppercase;letter-spacing:.1em}

/* ---------- Cards ---------- */
.cards{display:grid;gap:18px;grid-template-columns:repeat(auto-fill,minmax(280px,1fr))}
.card{
  background:var(--paper);border:1px solid var(--line);border-radius:var(--r);
  padding:22px;box-shadow:var(--shadow);display:flex;flex-direction:column;gap:10px;
  transition:transform .15s, box-shadow .15s, border-color .15s;
  position:relative;overflow:hidden;
}
.card:hover{transform:translateY(-2px);box-shadow:var(--shadow-lg);border-color:#cbd5e1}
.card h3{margin:0;font-size:1.1rem}
.card h3 a{color:var(--ink)}
.card .meta{font-family:var(--mono);font-size:.78rem;color:var(--muted);text-transform:uppercase;letter-spacing:.08em}
.card a.more{margin-top:auto;font-weight:600;display:inline-flex;align-items:center;gap:6px;color:var(--ink)}
.card a.more::after{content:"→";transition:transform .15s}
.card:hover a.more::after{transform:translateX(3px)}

/* Subject color stripe on cards */
.card.subject-life{border-top:3px solid var(--life)}
.card.subject-earth{border-top:3px solid var(--earth)}
.card.subject-phys{border-top:3px solid var(--phys)}

/* Periodic-table-style chip used as subject icon */
.chip{
  width:56px;height:56px;border-radius:10px;
  display:grid;grid-template-rows:auto 1fr;
  padding:6px 8px;font-family:var(--mono);color:#fff;
  position:relative;line-height:1;
}
.chip .num{font-size:.7rem;opacity:.85;text-align:left}
.chip .sym{font-size:1.6rem;font-weight:700;align-self:end;text-align:center;letter-spacing:-.02em}
.chip.life {background:linear-gradient(160deg,#16a34a,#0e7c3a)}
.chip.earth{background:linear-gradient(160deg,#1d4ed8,#1e40af)}
.chip.phys {background:linear-gradient(160deg,#ea580c,#c2410c)}
.chip.k2   {background:linear-gradient(160deg,#7c3aed,#5b21b6)}
.chip.g35  {background:linear-gradient(160deg,#0891b2,#0e7490)}
.chip.g68  {background:linear-gradient(160deg,#be185d,#9d174d)}

/* ---------- Worksheet grid (rows) ---------- */
.list{display:grid;gap:8px}
.list .row{
  display:grid;grid-template-columns:48px 1fr auto;gap:14px;align-items:center;
  padding:14px 16px;background:#fff;border:1px solid var(--line);border-radius:var(--r-sm);
  transition:border-color .12s, transform .12s;
}
.list .row:hover{border-color:#94a3b8;transform:translateX(2px)}
.list .row .num{font-family:var(--mono);font-size:.8rem;color:var(--muted);background:#f1f5f9;border-radius:8px;padding:6px;text-align:center}
.list .row .name{font-weight:600;color:var(--ink)}
.list .row .meta{color:var(--muted);font-size:.88rem}
.list .row .arrow{font-family:var(--mono);color:var(--muted)}
.list .row:hover .arrow{color:var(--ink)}

/* ---------- Tags ---------- */
.tag{
  display:inline-block;padding:3px 10px;border-radius:999px;
  font-family:var(--mono);font-size:.72rem;letter-spacing:.06em;text-transform:uppercase;font-weight:600;
  background:#f1f5f9;color:#334155;border:1px solid var(--line);
}
.tag.grade{background:#fef9c3;color:#854d0e;border-color:#fde68a}
.tag.std{background:#fce7f3;color:#9d174d;border-color:#fbcfe8}
.tag.life{background:var(--life-50);color:var(--life-700);border-color:var(--life-200)}
.tag.earth{background:var(--earth-50);color:var(--earth-700);border-color:var(--earth-200)}
.tag.phys{background:var(--phys-50);color:var(--phys-700);border-color:var(--phys-200)}

/* ---------- Two-column with sidebar ---------- */
.with-sidebar{display:grid;grid-template-columns:minmax(0,1fr) 320px;gap:36px}
@media (max-width:1020px){.with-sidebar{grid-template-columns:1fr}}
.sidebar{display:flex;flex-direction:column;gap:18px}
.box{background:#fff;border:1px solid var(--line);border-radius:var(--r);padding:18px;box-shadow:var(--shadow)}
.box h4{margin-top:0}
.box ul{list-style:none;padding:0;margin:0;display:flex;flex-direction:column;gap:8px}
.box ul li a{color:var(--ink);display:flex;justify-content:space-between;gap:8px}
.box ul li a:hover{color:var(--earth-700)}

/* ---------- AdSense placeholder ---------- */
.adslot{
  min-height:90px;border:1px dashed #d1d5db;background:repeating-linear-gradient(45deg,#fafafa 0 8px,#f3f4f6 8px 16px);
  border-radius:10px;display:grid;place-items:center;color:#9ca3af;font-family:var(--mono);font-size:.72rem;letter-spacing:.1em;text-transform:uppercase;margin:24px 0;
}

/* ---------- Editorial recommendation block ---------- */
.recs{background:#fff;border:1px solid var(--line);border-radius:var(--r);padding:22px;box-shadow:var(--shadow)}
.recs h4{margin:0 0 4px}
.recs .recs-sub{font-size:.85rem;color:var(--muted);margin:0 0 14px}
.recs ol{list-style:none;padding:0;margin:0;display:grid;gap:10px}
.recs ol li{padding:12px 14px;border-left:3px solid var(--earth);background:var(--earth-50);border-radius:8px}
.recs ol li:nth-child(2){border-color:var(--life);background:var(--life-50)}
.recs ol li:nth-child(3){border-color:var(--phys);background:var(--phys-50)}
.recs ol li:nth-child(4){border-color:#7c3aed;background:#f5f3ff}
.recs ol li:nth-child(5){border-color:#0891b2;background:#ecfeff}
.recs ol li:nth-child(6){border-color:#be185d;background:#fdf2f8}
.recs a,.recs .rec-title{color:var(--ink);font-weight:600;display:block}
.recs .rec-blurb{font-size:.85rem;color:var(--muted);margin:2px 0 0}

/* ---------- Prose ---------- */
.prose p{font-size:1.04rem;color:var(--ink-2)}
.prose ul{padding-left:1.2em}
.prose ul li{margin:.25em 0}
.prose .qa{counter-reset:q;list-style:none;padding:0;margin:0}
.prose .qa li{
  padding:14px 18px;background:#fff;border:1px solid var(--line);border-radius:var(--r-sm);
  margin-bottom:10px;display:grid;grid-template-columns:auto 1fr;gap:12px;align-items:baseline;
}
.prose .qa li::before{counter-increment:q;content:"Q" counter(q);font-family:var(--mono);font-weight:700;color:var(--earth-700);background:var(--earth-50);padding:4px 8px;border-radius:6px;font-size:.78rem}
.answer-key{counter-reset:q}
.answer-key li{background:var(--life-50);border-color:var(--life-200)}
.answer-key li::before{content:"A" counter(q);color:var(--life-700);background:#fff}

/* Reveal-on-click answer key */
details.answers{
  background:#fff;border:1px solid var(--line);border-radius:var(--r);padding:0;overflow:hidden;
  box-shadow:var(--shadow);margin:8px 0 24px;
}
details.answers > summary{
  list-style:none;cursor:pointer;padding:14px 18px;background:linear-gradient(180deg,#fff,#f8fafc);
  display:flex;align-items:center;justify-content:space-between;gap:12px;
  font-weight:700;color:var(--ink);
}
details.answers > summary::-webkit-details-marker{display:none}
details.answers > summary .hint{font-family:var(--mono);font-size:.78rem;color:var(--muted);font-weight:500;text-transform:uppercase;letter-spacing:.08em}
details.answers > summary .chev{transition:transform .15s;font-family:var(--mono)}
details.answers[open] > summary .chev{transform:rotate(90deg)}
details.answers > div.answers-body{padding:8px 18px 18px;border-top:1px dashed var(--line);background:linear-gradient(180deg,var(--life-50), #ffffff)}

.vocab-grid{display:grid;grid-template-columns:170px 1fr;gap:10px 16px;background:#fff;border:1px solid var(--line);border-radius:var(--r);padding:18px}
.vocab-grid dt{font-weight:700;font-family:var(--mono);font-size:.9rem;color:var(--ink)}
.vocab-grid dd{margin:0;color:var(--ink-2)}

/* ---------- Footer ---------- */
.site-footer{background:#0b1220;color:#cbd5e1;margin-top:64px;padding:48px 0 24px}
.site-footer .brand{color:#fff}
.site-footer h4{color:#fff;font-size:.85rem;text-transform:uppercase;letter-spacing:.08em;margin-bottom:12px}
.site-footer ul{list-style:none;padding:0;margin:0;display:flex;flex-direction:column;gap:8px}
.site-footer a{color:#cbd5e1}
.site-footer a:hover{color:#fff}
.footer-grid{display:grid;grid-template-columns:1.6fr 1fr 1fr 1fr;gap:32px;padding-bottom:32px}
.footer-recs{margin-top:24px;padding-top:24px;border-top:1px solid #1f2937}
.footer-recs h4{color:#fff}
.footer-recs ul{display:grid;grid-template-columns:repeat(auto-fill,minmax(220px,1fr));gap:10px}
.footer-recs ul li a,.footer-recs ul li .rec-title{color:#e2e8f0;border-left:2px solid #334155;padding-left:10px;display:block}
.footer-recs ul li a:hover{border-color:var(--accent);color:#fff}
.footer-bottom{border-top:1px solid #1f2937;padding-top:18px;font-family:var(--mono);font-size:.8rem;color:#94a3b8}
@media (max-width:860px){.footer-grid{grid-template-columns:1fr 1fr}}

/* ---------- Topic header strip ---------- */
.page-head{
  display:flex;align-items:center;gap:18px;margin-bottom:8px;
}
.page-head .chip{width:64px;height:64px;border-radius:12px}
.page-head .chip .sym{font-size:1.8rem}
.page-head .meta{font-family:var(--mono);font-size:.8rem;color:var(--muted)}

/* tag row */
.tag-row{display:flex;flex-wrap:wrap;gap:6px;margin:10px 0 18px}