/* ============================================================
   Physical Science 8 — an interactive online textbook
   Shared stylesheet
   ============================================================ */

@import url('https://fonts.googleapis.com/css2?family=Poppins:wght@300;400;500;600;700;800&display=swap');

:root{
  --ink:#1b1f2a;
  --ink-soft:#4a5063;
  --paper:#ffffff;
  --paper-soft:#f6f7fb;
  --line:#e6e8f0;
  --accent:#3a5ce4;
  --accent-dark:#28409e;
  --accent-tint:#eef1fd;
  --good:#2a9d6f;
  --bad:#e0483f;
  --radius:18px;
  --radius-sm:10px;
  --shadow:0 10px 30px -12px rgba(20,25,50,.18);
  --shadow-sm:0 4px 14px -6px rgba(20,25,50,.15);
  --maxw:1100px;
  color-scheme: light;
}

/* ---- per-unit accent themes ---- */
body[data-unit="u1"]{ --accent:#e63946; --accent-dark:#b3212c; --accent-tint:#fdeceD; }
body[data-unit="u2"]{ --accent:#6a4c93; --accent-dark:#4e3570; --accent-tint:#f1ecf7; }
body[data-unit="u3"]{ --accent:#1982c4; --accent-dark:#0f5f95; --accent-tint:#e9f4fb; }
body[data-unit="u4"]{ --accent:#00a0c4; --accent-dark:#00748d; --accent-tint:#e6f7fb; }
body[data-unit="u5"]{ --accent:#f77f00; --accent-dark:#c46200; --accent-tint:#fef1e2; }
body[data-unit="u6"]{ --accent:#2a9d6f; --accent-dark:#1d7a55; --accent-tint:#e9f7f1; }

*,*::before,*::after{ box-sizing:border-box; }
html{ scroll-behavior:smooth; }
body{
  margin:0;
  font-family:'Poppins',system-ui,-apple-system,Segoe UI,Roboto,sans-serif;
  color:var(--ink);
  background:var(--paper-soft);
  line-height:1.65;
  -webkit-font-smoothing:antialiased;
}
img,svg{ max-width:100%; }
a{ color:var(--accent-dark); text-decoration:none; }
a:hover{ text-decoration:underline; }
h1,h2,h3,h4{ font-weight:700; line-height:1.25; margin:0 0 .5em; color:var(--ink); }
p{ margin:0 0 1em; }
.container{ max-width:var(--maxw); margin:0 auto; padding:0 20px; }
button{ font-family:inherit; }

/* ---------------- top bar ---------------- */
.topbar{
  position:sticky; top:0; z-index:50;
  background:rgba(255,255,255,.92);
  backdrop-filter:blur(8px);
  border-bottom:1px solid var(--line);
}
.topbar-inner{
  max-width:var(--maxw); margin:0 auto; padding:12px 20px;
  display:flex; align-items:center; gap:14px;
}
.brand{ display:flex; align-items:center; gap:10px; font-weight:700; font-size:1.05rem; color:var(--ink); white-space:nowrap;}
.brand .dot{ width:12px; height:12px; border-radius:50%; background:var(--accent); box-shadow:0 0 0 4px var(--accent-tint); flex:none; }
.brand small{ display:block; font-weight:400; font-size:.72rem; color:var(--ink-soft); }
.menu-btn{
  border:1px solid var(--line); background:#fff; border-radius:999px;
  padding:9px 16px; font-weight:600; cursor:pointer; display:flex; gap:8px; align-items:center;
  color:var(--ink); margin-left:auto;
}
.menu-btn:hover{ border-color:var(--accent); color:var(--accent-dark); }
.topbar nav.inline-links{ display:flex; gap:4px; margin-left:auto; }
.topbar nav.inline-links a{
  padding:8px 14px; border-radius:999px; color:var(--ink-soft); font-weight:600; font-size:.92rem;
}
.topbar nav.inline-links a:hover, .topbar nav.inline-links a.active{ background:var(--accent-tint); color:var(--accent-dark); text-decoration:none; }
@media (max-width:760px){ .topbar nav.inline-links{ display:none; } }

/* ---------------- drawer / table of contents ---------------- */
.drawer-backdrop{
  position:fixed; inset:0; background:rgba(15,18,30,.45); z-index:80; opacity:0; pointer-events:none; transition:opacity .25s;
}
.drawer-backdrop.open{ opacity:1; pointer-events:auto; }
.drawer{
  position:fixed; top:0; right:-380px; width:340px; max-width:88vw; height:100%; background:#fff; z-index:90;
  box-shadow:-15px 0 40px rgba(0,0,0,.25); transition:right .28s ease; overflow-y:auto; padding:22px 18px 60px;
}
.drawer.open{ right:0; }
.drawer h3{ font-size:1rem; text-transform:uppercase; letter-spacing:.04em; color:var(--ink-soft); margin:22px 0 8px; }
.drawer h3:first-of-type{ margin-top:6px; }
.drawer-close{ float:right; border:none; background:var(--paper-soft); width:34px; height:34px; border-radius:50%; font-size:1.1rem; cursor:pointer; }
.drawer .unit-block{ border-left:3px solid var(--line); padding-left:12px; margin-bottom:6px; }
.drawer .unit-block.current{ border-left-color:var(--accent); }
.drawer .unit-title{ display:block; font-weight:700; font-size:.88rem; padding:8px 0 4px; color:var(--ink); }
.drawer .unit-title span{ color:var(--ink-soft); font-weight:500; }
.drawer ul{ list-style:none; margin:0 0 10px; padding:0; }
.drawer li a{
  display:flex; align-items:center; gap:8px; padding:7px 6px; border-radius:8px; color:var(--ink-soft); font-size:.9rem; font-weight:500;
}
.drawer li a:hover{ background:var(--paper-soft); text-decoration:none; }
.drawer li a.active{ background:var(--accent-tint); color:var(--accent-dark); font-weight:700; }
.check{ width:16px; height:16px; border-radius:50%; border:2px solid var(--line); flex:none; display:inline-block; }
.check.done{ background:var(--good); border-color:var(--good); position:relative; }
.check.done::after{ content:"✓"; position:absolute; inset:0; color:#fff; font-size:10px; display:flex; align-items:center; justify-content:center; }

/* ---------------- hero / banner ---------------- */
.hero{
  background:linear-gradient(150deg,var(--accent-tint), #fff 65%);
  border-bottom:1px solid var(--line);
}
.hero-inner{
  max-width:var(--maxw); margin:0 auto; padding:46px 20px 40px;
  display:grid; grid-template-columns:1fr 200px; gap:30px; align-items:center;
}
.hero.hero-page{ padding-top:8px; }
.eyebrow{
  display:inline-flex; align-items:center; gap:8px; font-weight:700; font-size:.78rem;
  text-transform:uppercase; letter-spacing:.06em; color:var(--accent-dark); background:#fff;
  border:1px solid var(--line); padding:6px 14px; border-radius:999px; margin-bottom:14px;
}
.hero h1{ font-size:clamp(1.7rem,4vw,2.5rem); margin-bottom:.35em; }
.hero .lede{ font-size:1.08rem; color:var(--ink-soft); max-width:60ch; }
.hero-icon{ justify-self:end; }
.hero-icon svg{ width:170px; height:170px; }
@media (max-width:700px){ .hero-inner{ grid-template-columns:1fr; } .hero-icon{ display:none; } }

/* ---------------- big-question / callout ---------------- */
.callout{
  background:#fff; border:1px solid var(--line); border-left:6px solid var(--accent);
  border-radius:var(--radius-sm); padding:18px 22px; margin:26px 0; box-shadow:var(--shadow-sm);
}
.callout .label{ font-weight:700; font-size:.78rem; text-transform:uppercase; letter-spacing:.05em; color:var(--accent-dark); margin-bottom:6px; }
.callout p{ margin:0; font-size:1.08rem; font-weight:500; }

/* ---------------- main layout ---------------- */
main{ padding:36px 0 70px; }
.prose{ max-width:74ch; }
.prose h2{ font-size:1.4rem; margin-top:2.2em; padding-top:.2em; border-top:1px solid var(--line); }
.prose h2:first-child{ border-top:none; margin-top:0; }
.prose p{ color:var(--ink-soft); font-size:1.02rem; }

/* chapter body: prose column + a margin rail reserved for vocabulary pop-outs */
.chapter-body{ display:grid; grid-template-columns:minmax(0,74ch) minmax(220px,260px); gap:40px; align-items:start; position:relative; }
.chapter-body .prose{ max-width:none; }
.margin-rail{ position:relative; }
@media (max-width:980px){
  .chapter-body{ display:block; }
  .margin-rail{ display:none; }
}

/* ---------------- clickable glossary terms ---------------- */
.gloss-term{
  border-bottom:2px dotted var(--accent); color:var(--accent-dark); font-weight:600;
  cursor:pointer; border-radius:3px; padding:0 1px;
}
.gloss-term:hover{ background:var(--accent-tint); }
.gloss-term.active{ background:var(--accent-tint); }
.term-popout{
  position:absolute; left:0; right:0; background:#fff; border:1px solid var(--line);
  border-left:5px solid var(--accent); border-radius:12px; padding:16px 18px 18px;
  box-shadow:var(--shadow); font-size:.86rem; z-index:30; animation:popIn .16s ease;
}
.term-popout .pt-term{ font-weight:800; margin-bottom:6px; color:var(--ink); font-size:.95rem; padding-right:20px; }
.term-popout .pt-def{ color:var(--ink-soft); line-height:1.55; margin:0; }
.term-popout .pt-close{
  position:absolute; top:10px; right:12px; border:none; background:none; font-size:1.15rem;
  line-height:1; cursor:pointer; color:var(--ink-soft); padding:2px 4px;
}
.term-popout .pt-close:hover{ color:var(--ink); }
@keyframes popIn{ from{ opacity:0; transform:translateY(6px); } to{ opacity:1; transform:translateY(0); } }

/* mobile: pop-out becomes a bottom sheet since there's no side margin to use */
.term-popout.mobile{
  position:fixed; left:14px; right:14px; bottom:14px; z-index:200;
  box-shadow:0 -12px 34px rgba(0,0,0,.25); animation:popUp .18s ease;
}
@keyframes popUp{ from{ opacity:0; transform:translateY(16px); } to{ opacity:1; transform:translateY(0); } }
.term-popout-backdrop{ position:fixed; inset:0; background:rgba(15,18,30,.35); z-index:190; opacity:0; pointer-events:none; transition:opacity .18s; }
.term-popout-backdrop.show{ opacity:1; pointer-events:auto; }

.section-figure{ margin:18px 0 26px; background:#fff; border:1px solid var(--line); border-radius:var(--radius-sm); padding:16px 18px; box-shadow:var(--shadow-sm); }
.section-figure figcaption{ font-size:.85rem; color:var(--ink-soft); margin-top:8px; text-align:center; }

/* ---------------- unit index cards (homepage) ---------------- */
.unit-grid{ display:grid; grid-template-columns:repeat(auto-fit,minmax(280px,1fr)); gap:20px; margin:26px 0 10px; }
.unit-card{
  background:#fff; border:1px solid var(--line); border-radius:var(--radius); padding:22px; box-shadow:var(--shadow-sm);
  display:flex; flex-direction:column; gap:10px; border-top:6px solid var(--card-accent,var(--accent));
  transition:transform .15s, box-shadow .15s;
}
.unit-card:hover{ transform:translateY(-3px); box-shadow:var(--shadow); text-decoration:none; }
.unit-card .num{ font-weight:800; font-size:.78rem; letter-spacing:.06em; text-transform:uppercase; color:var(--card-accent,var(--accent)); }
.unit-card h3{ margin:0; font-size:1.15rem; color:var(--ink); }
.unit-card p{ color:var(--ink-soft); font-size:.92rem; margin:0; flex:1; }
.unit-card .icon{ width:52px; height:52px; }
.unit-card .icon svg{ width:100%; height:100%; color:var(--card-accent,var(--accent)); }
.unit-card .meta{ font-size:.82rem; color:var(--ink-soft); font-weight:600; }

.topic-list{ list-style:none; margin:18px 0; padding:0; display:grid; gap:10px; }
.topic-list li a{
  display:flex; align-items:center; gap:14px; background:#fff; border:1px solid var(--line);
  border-radius:var(--radius-sm); padding:14px 16px; color:var(--ink); font-weight:600; box-shadow:var(--shadow-sm);
}
.topic-list li a:hover{ border-color:var(--accent); text-decoration:none; }
.topic-list .tnum{
  width:34px; height:34px; border-radius:50%; background:var(--accent-tint); color:var(--accent-dark);
  display:flex; align-items:center; justify-content:center; font-weight:800; font-size:.85rem; flex:none;
}
.topic-list .ticon{ width:26px; height:26px; flex:none; }
.topic-list .ticon svg{ width:100%; height:100%; color:var(--accent); }
.topic-list .tq{ font-weight:400; color:var(--ink-soft); font-size:.85rem; display:block; margin-top:2px; }

/* ---------------- vocabulary ---------------- */
.vocab-grid{ display:grid; grid-template-columns:repeat(auto-fill,minmax(230px,1fr)); gap:14px; margin:18px 0 10px; }
.vcard{
  perspective:1200px; height:130px; cursor:pointer;
}
.vcard-inner{
  position:relative; width:100%; height:100%; transition:transform .5s; transform-style:preserve-3d;
}
.vcard.flipped .vcard-inner{ transform:rotateY(180deg); }
.vface{
  position:absolute; inset:0; backface-visibility:hidden; border-radius:var(--radius-sm);
  padding:14px 16px; display:flex; align-items:center; justify-content:center; text-align:center;
  box-shadow:var(--shadow-sm); border:1px solid var(--line);
}
.vface.front{ background:#fff; font-weight:700; font-size:1.02rem; }
.vface.back{ background:var(--accent); color:#fff; transform:rotateY(180deg); font-size:.87rem; font-weight:500; }
.vcard .hint{ position:absolute; bottom:6px; right:10px; font-size:.68rem; color:var(--ink-soft); font-weight:600; opacity:.7; }
.vface.back .hint{ display:none; }

/* ---------------- real-world examples + meet-the-scientist ---------------- */
.examples-grid{ display:grid; grid-template-columns:repeat(auto-fit,minmax(240px,1fr)); gap:16px; margin:18px 0 14px; }
.example-card{
  background:#fff; border:1px solid var(--line); border-radius:var(--radius-sm); padding:16px 18px;
  box-shadow:var(--shadow-sm); border-top:4px solid var(--accent);
}
.example-card h4{ margin:0 0 6px; font-size:1rem; }
.example-card p{ margin:0; color:var(--ink-soft); font-size:.92rem; }
.connection-note{
  display:flex; gap:10px; align-items:flex-start; background:var(--accent-tint); border-radius:var(--radius-sm);
  padding:14px 18px; margin:4px 0 8px; font-size:.92rem; color:var(--ink);
}
.connection-note .tag{ flex:none; font-weight:800; font-size:.72rem; text-transform:uppercase; letter-spacing:.05em; color:var(--accent-dark); }
.scientist-card{
  display:flex; gap:18px; align-items:flex-start; background:#fff; border:1px solid var(--line);
  border-radius:var(--radius); padding:20px 22px; margin:18px 0 8px; box-shadow:var(--shadow-sm);
}
.scientist-card .savatar{
  flex:none; width:56px; height:56px; border-radius:50%; background:var(--accent); color:#fff;
  display:flex; align-items:center; justify-content:center; font-size:1.5rem; font-weight:800;
}
.scientist-card h4{ margin:0 0 6px; font-size:1.08rem; }
.scientist-card p{ margin:0; color:var(--ink-soft); font-size:.94rem; }

/* ---------------- resource cards ---------------- */
.resource-grid{ display:grid; grid-template-columns:repeat(auto-fit,minmax(260px,1fr)); gap:16px; margin:18px 0; }
.rcard{ background:#fff; border:1px solid var(--line); border-radius:var(--radius-sm); overflow:hidden; box-shadow:var(--shadow-sm); display:flex; flex-direction:column; }
.rcard .rtag{
  font-size:.7rem; font-weight:800; text-transform:uppercase; letter-spacing:.06em; padding:8px 14px;
  background:var(--accent-tint); color:var(--accent-dark);
}
.rcard .rbody{ padding:14px 16px 16px; display:flex; flex-direction:column; gap:6px; flex:1; }
.rcard h4{ margin:0; font-size:1rem; }
.rcard .rsource{ font-size:.8rem; color:var(--ink-soft); }
.rcard .rlink{ margin-top:auto; font-weight:700; font-size:.9rem; display:inline-flex; align-items:center; gap:6px; }
.video-embed{ position:relative; width:100%; padding-top:56.25%; background:#000; }
.video-embed iframe{ position:absolute; inset:0; width:100%; height:100%; border:0; }

/* ---------------- quiz ---------------- */
.quiz{ background:#fff; border:1px solid var(--line); border-radius:var(--radius); padding:24px 26px 26px; box-shadow:var(--shadow-sm); margin-top:14px; }
.quiz-q{ margin-bottom:22px; padding-bottom:20px; border-bottom:1px dashed var(--line); }
.quiz-q:last-of-type{ border-bottom:none; margin-bottom:6px; }
.quiz-q p.qtext{ font-weight:600; margin-bottom:10px; color:var(--ink); }
.quiz-choices{ display:grid; gap:8px; }
.qchoice{
  display:flex; align-items:center; gap:10px; border:1.5px solid var(--line); border-radius:var(--radius-sm);
  padding:10px 14px; cursor:pointer; font-size:.94rem; background:var(--paper-soft); transition:.15s;
}
.qchoice:hover{ border-color:var(--accent); }
.qchoice input{ accent-color:var(--accent); width:16px; height:16px; flex:none; }
.qchoice.correct{ background:#e8f8f0; border-color:var(--good); }
.qchoice.incorrect{ background:#fdecec; border-color:var(--bad); }
.qfeedback{ font-size:.86rem; margin-top:8px; padding:8px 12px; border-radius:8px; display:none; }
.qfeedback.show{ display:block; }
.qfeedback.right{ background:#e8f8f0; color:#1c6b4b; }
.qfeedback.wrong{ background:#fdecec; color:#a3352d; }
.quiz-actions{ display:flex; align-items:center; gap:14px; flex-wrap:wrap; margin-top:6px; }
.btn{
  border:none; background:var(--accent); color:#fff; font-weight:700; padding:12px 22px; border-radius:999px;
  cursor:pointer; font-size:.95rem; box-shadow:var(--shadow-sm);
}
.btn:hover{ background:var(--accent-dark); }
.btn.secondary{ background:#fff; color:var(--ink); border:1.5px solid var(--line); box-shadow:none; }
.btn.secondary:hover{ border-color:var(--accent); color:var(--accent-dark); }
.quiz-score{ font-weight:700; }
.quiz-score.good{ color:var(--good); }
.quiz-score.bad{ color:var(--bad); }

/* ---------------- prev/next + footer ---------------- */
.chapter-nav{ display:flex; justify-content:space-between; gap:16px; margin-top:50px; flex-wrap:wrap; }
.chapter-nav a{
  flex:1; min-width:220px; background:#fff; border:1px solid var(--line); border-radius:var(--radius-sm);
  padding:16px 18px; box-shadow:var(--shadow-sm); color:var(--ink);
}
.chapter-nav a:hover{ border-color:var(--accent); text-decoration:none; }
.chapter-nav .dir{ font-size:.72rem; text-transform:uppercase; letter-spacing:.05em; color:var(--ink-soft); font-weight:700; display:block; margin-bottom:4px;}
.chapter-nav .next{ text-align:right; }

footer{ border-top:1px solid var(--line); padding:30px 0; color:var(--ink-soft); font-size:.85rem; text-align:center; }

/* glossary */
.glossary-search{ width:100%; max-width:420px; padding:12px 16px; border-radius:999px; border:1.5px solid var(--line); font-size:1rem; margin:8px 0 24px; font-family:inherit; }
.glossary-letter{ font-weight:800; font-size:1.3rem; margin:28px 0 10px; color:var(--accent-dark); }
.gterm{ background:#fff; border:1px solid var(--line); border-radius:var(--radius-sm); padding:14px 18px; margin-bottom:10px; box-shadow:var(--shadow-sm); }
.gterm b{ display:block; margin-bottom:2px; }
.gterm .gunit{ font-size:.76rem; color:var(--accent-dark); font-weight:700; text-transform:uppercase; }

.badge{ display:inline-block; background:var(--accent-tint); color:var(--accent-dark); font-weight:700; font-size:.72rem; padding:4px 10px; border-radius:999px; text-transform:uppercase; letter-spacing:.04em; }

@media (max-width:700px){
  .hero-inner{ padding-top:30px; }
  .prose{ max-width:none; }
}