/* Plant Physiology and Metabolism — BOT-DSM-511. Plain-CSS fallback: readable without any CDN. */
:root{--ink:#1f2937;--muted:#5b6470;--line:#e5e7eb;--paper:#fffdf8;--green:#2f5d3a;--green2:#e8f0e6;--accent:#b45309;--radius:14px}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;background:var(--paper);color:var(--ink);font-family:Georgia,serif;font-size:17px;line-height:1.75}
body,button,input{font-family:Georgia,serif}
header.site{position:sticky;top:0;z-index:20;background:#fff;border-bottom:1px solid var(--line)}
.nav{max-width:760px;margin:0 auto;padding:12px 18px;display:flex;gap:14px;align-items:center;flex-wrap:wrap}
.nav a{color:var(--ink);text-decoration:none;font-family:Arial,Helvetica,sans-serif;font-size:15px}
.nav a.brand{font-weight:700;color:var(--green);font-size:18px}
.nav a:hover{text-decoration:underline}
main{max-width:760px;margin:0 auto;padding:22px 18px 80px}
h1,h2,h3{font-family:Georgia,serif;line-height:1.25;color:#14281a}
h1{font-size:2rem} h2{font-size:1.55rem;margin-top:2.2rem;border-top:1px solid var(--line);padding-top:1.2rem} h3{font-size:1.25rem;margin-top:1.6rem}
p,li{font-family:Arial,Helvetica,sans-serif;font-size:17px;line-height:1.7}
a{color:var(--green)}
.card{border:1px solid var(--line);border-radius:var(--radius);padding:18px;background:#fff;margin:14px 0}
.def{border-left:5px solid var(--green);background:var(--green2);padding:14px 18px;border-radius:0 12px 12px 0}
.trap{background:#fef3c7;border:1px solid #fcd34d;border-radius:12px;padding:14px 18px}
.flow{display:flex;flex-direction:column;gap:0;margin:16px 0}
.flow-step{border:1px solid var(--line);background:#fff;border-radius:10px;padding:12px 14px;position:relative}
.flow-arrow{text-align:center;color:var(--green);font-weight:700;line-height:1.2}
table{width:100%;border-collapse:collapse;margin:14px 0;font-family:Arial,Helvetica,sans-serif;font-size:15px;line-height:1.5}
@media(max-width:600px){table{display:block;overflow-x:auto}}
th,td{border:1px solid var(--line);padding:9px;text-align:left;vertical-align:top}
th{background:var(--green2)}
figure{margin:20px 0} figure img,figure svg{width:100%;height:auto;border:1px solid var(--line);border-radius:12px;background:#fff}
figcaption{font-family:Arial,Helvetica,sans-serif;font-size:14px;color:var(--muted);margin-top:8px;line-height:1.5}
button,.btn{display:inline-block;border:1px solid var(--green);background:var(--green);color:#fff;padding:10px 16px;border-radius:999px;cursor:pointer;font-family:Arial,Helvetica,sans-serif;font-size:15px;text-decoration:none}
button.secondary,.btn.secondary{background:#fff;color:var(--green)}
.quiz-q,.key{border:1px solid var(--line);border-radius:12px;padding:16px;background:#fff;margin:14px 0}
.answer{display:none;margin-top:12px;padding:12px;background:var(--green2);border-radius:10px}
.answer.open{display:block}
.opt{width:100%;text-align:left;background:#fff;color:var(--ink);border:1px solid var(--line);margin:6px 0}
.opt:hover{border-color:var(--green)}
.searchbox{width:100%;padding:12px;border:1px solid var(--line);border-radius:10px;font-size:16px}
.toc{background:#fff;border:1px solid var(--line);border-radius:12px;padding:14px 18px}
.toc a{display:block;padding:3px 0}
.small{font-size:14px;color:var(--muted);font-family:Arial,Helvetica,sans-serif}
.pill{display:inline-block;background:var(--green2);color:var(--green);border-radius:999px;padding:3px 10px;font-family:Arial,Helvetica,sans-serif;font-size:13px;margin:2px}
#topBtn{position:fixed;right:16px;bottom:16px;display:none}
.checklist label{display:block;padding:6px 0;font-family:Arial,Helvetica,sans-serif}
@media(min-width:900px){main{max-width:780px} h1{font-size:2.4rem} body{font-size:18px}}
@media print{header.site,#topBtn,.searchbox{display:none} main{max-width:100%}}

/* --- Rebuild: mobile-first responsive, header/footer, progress --- */
html,body{overflow-x:hidden}
img,svg,video{max-width:100%;height:auto}
figure svg text{font-family:Arial,Helvetica,sans-serif}
table{display:block;overflow-x:auto;width:100%}
table table{display:table}
.nav{row-gap:8px}
.nav a{padding:6px 4px}
.header-progress{margin-left:auto;font-family:Arial,Helvetica,sans-serif;font-size:13px;background:var(--green2);color:var(--green);border-radius:999px;padding:4px 10px;white-space:nowrap}
footer.site{border-top:1px solid var(--line);background:#fff;margin-top:20px}
.footer-inner{max-width:780px;margin:0 auto;padding:22px 18px 40px;font-family:Arial,Helvetica,sans-serif;font-size:14px;line-height:1.6;color:var(--muted)}
.footer-inner a{margin-right:10px;display:inline-block;padding:3px 0}
.progress-bar{height:12px;background:var(--line);border-radius:999px;overflow:hidden;margin:8px 0}
.progress-bar > span{display:block;height:100%;background:var(--green);border-radius:999px}
.unit-progress{border:1px solid var(--line);border-radius:12px;padding:14px 16px;background:#fff;margin:10px 0}
.unit-progress p{margin:4px 0}
.opt{width:100%;min-height:48px}
.quiz-opt.correct{border-color:#2f5d3a;border-width:2px;background:#e8f0e6}
.quiz-opt.wrong{border-color:#b45309;border-width:2px;background:#fef3c7}
@media(max-width:600px){
  main{padding:16px 14px 60px}
  h1{font-size:1.6rem} h2{font-size:1.3rem} h3{font-size:1.15rem}
  body,p,li{font-size:17px}
  .nav{padding:10px 14px}
  .nav a.brand{width:100%}
  .header-progress{margin-left:0}
  .btn,button.btn{display:block;width:100%;text-align:center;margin:8px 0}
  .opt{font-size:16px;padding:12px 14px}
  figure{margin:16px 0}
  .footer-inner{padding:18px 14px 36px}
}
@media(min-width:900px){.footer-inner{max-width:780px}}

/* --- Final version: toggle menu, redesigned back-to-top, section polish --- */
header.site{transition:box-shadow .2s ease}
header.site.scrolled{box-shadow:0 4px 18px rgba(20,40,26,.12)}
.nav{position:relative;align-items:center}
.nav-primary{display:flex;gap:16px;align-items:center}
.nav-primary a{padding:6px 2px}
.menu-toggle{margin-left:0;display:inline-flex;align-items:center;gap:8px;background:#fff;color:var(--green);border:1px solid var(--green);padding:8px 14px;border-radius:999px;font-size:15px}
.menu-toggle[aria-expanded="true"]{background:var(--green);color:#fff}
.site-menu{position:absolute;left:18px;right:18px;top:calc(100% + 6px);background:#fff;border:1px solid var(--line);border-radius:14px;box-shadow:0 12px 30px rgba(20,40,26,.14);padding:14px 18px;z-index:30;display:grid;grid-template-columns:1fr 1fr;gap:2px 24px}
.site-menu[hidden]{display:none}
.site-menu a{display:block;padding:7px 0;color:var(--ink);text-decoration:none;font-family:Arial,Helvetica,sans-serif;font-size:15px}
.site-menu a:hover{color:var(--green);text-decoration:underline}
.menu-heading{grid-column:1 / -1;margin:10px 0 2px;font-family:Arial,Helvetica,sans-serif;font-size:13px;letter-spacing:.06em;text-transform:uppercase;color:var(--muted)}
.menu-heading:first-child{margin-top:0}
.to-top{position:fixed;right:20px;bottom:20px;z-index:40;width:56px;height:56px;border-radius:50%;border:none;background:var(--green);color:#fff;display:flex;align-items:center;justify-content:center;box-shadow:0 8px 24px rgba(20,40,26,.35);cursor:pointer;opacity:0;pointer-events:none;transform:translateY(8px);transition:opacity .25s ease,transform .25s ease,background .2s ease}
.to-top:hover{background:#24452c}
.to-top.show{opacity:1;pointer-events:auto;transform:translateY(0)}
.to-top.raised{bottom:96px}
section{scroll-margin-top:96px}
section.topic{padding-top:4px}
section.topic h2,section.topic h3{margin-bottom:.6rem}
figure{background:#fff;border:1px solid var(--line);border-radius:14px;padding:12px}
figure img,figure svg{border:none;border-radius:8px}
figcaption{padding:4px 4px 2px}
.card{box-shadow:0 1px 4px rgba(20,40,26,.06)}
.footer-nav{display:flex;flex-wrap:wrap;gap:4px 14px;margin:12px 0}
.footer-nav a{margin-right:0}
.footer-title{color:var(--ink)}
@media(max-width:600px){
  .nav-primary{display:none}
  .nav{padding:12px 14px}
  .nav a.brand{width:auto;flex:1}
  .header-progress{margin-left:0;order:3}
  .menu-toggle{margin-left:auto}
  .site-menu{left:14px;right:14px;grid-template-columns:1fr}
  .to-top{right:16px;bottom:16px;width:52px;height:52px}
  .to-top.raised{bottom:88px}
  main{padding-bottom:110px}
}
@media print{header.site,.to-top,.site-menu{display:none!important}}
/* Override the legacy #topBtn display rule so the new .to-top show/hide (opacity) works. */
#topBtn{display:flex}
#topBtn.to-top{position:fixed}