/* ScienceStar — shared stylesheet for O-Level Pure Science topic pages
   (Chemistry, Physics, Biology). Used by all 33 topic pages under
   /secondary-science/pure-sciences/{chemistry,physics,biology}/.

   Each page keeps a small inline <style> override (in the <head>, right
   after the <link> to this file) that sets the subject's accent colour
   via the --acc / --rgb variables, plus five small rules that differ by
   subject (.section h3, .tp-fill, .tp-count, .eq-box, .eq-label, and the
   print-mode .formula background). Everything else lives here. */

*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}html{scroll-behavior:smooth;-webkit-font-smoothing:antialiased}
body{font-family:'DM Sans',system-ui,sans-serif;background:var(--bg);color:var(--text);line-height:1.65}
nav{position:fixed;top:0;left:0;right:0;z-index:100;height:60px;display:flex;align-items:center;padding:0 clamp(16px,5%,56px);background:rgba(8,15,30,.9);backdrop-filter:blur(20px);border-bottom:1px solid var(--border)}
.nav-brand{font-family:'Sora',sans-serif;font-weight:800;font-size:18px;color:#fff;text-decoration:none}.nav-brand span{color:var(--sky)}
.nav-links{display:flex;align-items:center;gap:4px;margin-left:auto;flex-wrap:wrap}
.nav-links a{font-size:12px;font-weight:600;color:var(--muted);text-decoration:none;padding:5px 10px;border-radius:8px;transition:.15s}.nav-links a:hover{color:#fff;background:rgba(255,255,255,.08)}
.npill{padding:5px 12px!important;border-radius:50px!important;font-weight:700!important;font-size:11px!important;color:#fff!important}
.np3{background:var(--p3)!important}.np4{background:var(--p4)!important}.np5{background:var(--p5)!important;color:#0d1629!important}.npsle{background:var(--sky2)!important}.nsec{background:var(--hub)!important}
.crumb{font-size:12px;color:var(--dim);padding:76px clamp(16px,5%,56px) 0;max-width:900px;margin:0 auto}.crumb a{color:var(--muted);text-decoration:none}.crumb a:hover{color:var(--acc)}.crumb span{margin:0 5px}
.hero{padding:28px clamp(16px,5%,56px) 40px;border-bottom:1px solid var(--border);position:relative;overflow:hidden}
.hero::before{content:"";position:absolute;inset:0;background:linear-gradient(135deg,rgba(var(--rgb),.08),transparent 60%)}
.hero-in{max-width:900px;margin:0 auto;position:relative;z-index:1}
.topic-num{font-size:11px;font-weight:800;letter-spacing:1.5px;text-transform:uppercase;color:var(--dim);margin-bottom:8px}
h1{font-family:'Sora',sans-serif;font-size:clamp(26px,3.5vw,38px);font-weight:800;color:#fff;line-height:1.1;margin-bottom:10px}
.hero-meta{display:flex;flex-wrap:wrap;gap:8px;margin-top:12px}
.hmeta{font-size:11px;font-weight:700;padding:4px 10px;border-radius:50px;background:rgba(var(--rgb),.1);border:1px solid rgba(var(--rgb),.25);color:var(--acc)}
.content{max-width:900px;margin:0 auto;padding:clamp(28px,4vw,48px) clamp(16px,5%,56px)}
.toc{background:var(--card);border:1px solid var(--border);border-radius:12px;padding:18px 20px;margin-bottom:32px}
.toc h2{font-family:'Sora',sans-serif;font-size:13px;font-weight:800;color:var(--dim);text-transform:uppercase;letter-spacing:1px;margin-bottom:10px}
.toc ol{padding-left:18px;display:grid;gap:5px}
.toc a{font-size:13px;color:var(--muted);text-decoration:none;transition:.15s}.toc a:hover{color:var(--acc)}
.section{margin-bottom:40px;scroll-margin-top:80px}
.section h2{font-family:'Sora',sans-serif;font-size:clamp(18px,2.2vw,22px);font-weight:800;color:#fff;margin-bottom:14px;padding-bottom:10px;border-bottom:1px solid var(--border)}
/* .section h3 colour is subject-specific — set in each page's override block */
.section p{font-size:15px;color:var(--muted);line-height:1.8;margin-bottom:12px}
.section ul,.section ol{padding-left:20px;margin-bottom:12px}
.section li{font-size:15px;color:var(--muted);line-height:1.75;margin-bottom:5px}
.def{background:rgba(var(--rgb),.06);border-left:3px solid var(--acc);border-radius:0 10px 10px 0;padding:14px 16px;margin:14px 0}
.def strong{color:#fff;font-size:14px;display:block;margin-bottom:4px}.def p{font-size:14px;color:var(--muted);margin:0;line-height:1.65}
.formula{background:rgba(var(--rgb),.08);border:1px solid rgba(var(--rgb),.25);border-radius:10px;padding:14px 18px;margin:14px 0;font-family:'Sora',sans-serif;font-size:16px;font-weight:800;color:#fff;text-align:center}
.formula span{display:block;font-family:'DM Sans',sans-serif;font-size:12px;font-weight:400;color:var(--muted);margin-top:6px}
.tbl{width:100%;border-collapse:collapse;margin:14px 0;font-size:14px}
.tbl th{background:var(--bg2);padding:10px 12px;text-align:left;font-weight:700;color:var(--text);border-bottom:1px solid var(--border2)}
.tbl td{padding:9px 12px;border-bottom:1px solid var(--border);color:var(--muted)}
.tbl tr:last-child td{border-bottom:none}.tbl tr:nth-child(even) td{background:rgba(255,255,255,.02)}
.trap{background:rgba(248,113,113,.07);border-left:3px solid var(--red);border-radius:0 10px 10px 0;padding:14px 16px;margin:16px 0}
.trap-head{font-size:11px;font-weight:800;text-transform:uppercase;letter-spacing:.8px;color:var(--red);margin-bottom:6px}
.trap p{font-size:14px;color:var(--muted);margin:0;line-height:1.65}
.tip{background:rgba(52,211,153,.06);border-left:3px solid var(--green);border-radius:0 10px 10px 0;padding:14px 16px;margin:16px 0}
.tip-head{font-size:11px;font-weight:800;text-transform:uppercase;letter-spacing:.8px;color:var(--green);margin-bottom:6px}
.tip p{font-size:14px;color:var(--muted);margin:0;line-height:1.65}
.worked{background:rgba(251,191,36,.06);border:1px solid rgba(251,191,36,.2);border-radius:10px;padding:16px 18px;margin:16px 0}
.worked-head{font-size:11px;font-weight:800;text-transform:uppercase;letter-spacing:.8px;color:var(--amber);margin-bottom:8px}
.worked p{font-size:14px;color:var(--muted);line-height:1.75;margin-bottom:6px}.worked p:last-child{margin-bottom:0}
.worked strong{color:#fff}
.topic-nav{display:flex;justify-content:space-between;margin:48px 0 20px;gap:12px;flex-wrap:wrap}
.tnav-btn{flex:1;min-width:160px;background:var(--card);border:1px solid var(--border);border-radius:12px;padding:14px 16px;text-decoration:none;transition:.2s}.tnav-btn:hover{border-color:var(--border2)}
.tnav-dir{font-size:10px;font-weight:700;text-transform:uppercase;letter-spacing:.8px;color:var(--dim);margin-bottom:4px}
.tnav-title{font-size:14px;font-weight:700;color:#fff}
footer{background:#040a14;border-top:1px solid var(--border);padding:40px clamp(16px,5%,56px) 24px}
.fi{max-width:1100px;margin:0 auto;display:grid;grid-template-columns:2fr 1fr 1fr 1fr;gap:28px;margin-bottom:24px}
.flogo{font-family:'Sora',sans-serif;font-weight:800;font-size:17px;color:#fff;text-decoration:none}.flogo span{color:var(--sky)}
.fcol h4{font-size:11px;font-weight:700;letter-spacing:1.5px;text-transform:uppercase;color:var(--dim);margin-bottom:10px}
.fcol a{display:block;font-size:13px;color:var(--muted);text-decoration:none;margin-bottom:7px}.fcol a:hover{color:#fff}
.fb{max-width:1100px;margin:0 auto;padding-top:16px;border-top:1px solid var(--border);font-size:12px;color:var(--dim)}
@media(max-width:700px){.fi{grid-template-columns:1fr 1fr}.nav-links .npill{display:none}}

/* print-mode formula background is subject-specific — set in page override,
   which adds its own small @media print block; browsers merge them. */
@media print{nav,footer,.topic-nav{display:none}body{background:#fff;color:#111}.content{padding:16px}.section h2{color:#111;border-color:#ddd}.section p,.section li,.def p,.trap p,.tip p,.worked p{color:#333}.tbl th{background:#f1f5f9;color:#111}.tbl td{color:#444}}

.quiz-section{margin:48px 0;border-top:1px solid var(--border);padding-top:32px}
.quiz-section h2{font-family:'Sora',sans-serif;font-size:20px;font-weight:800;color:#fff;margin-bottom:6px}
.quiz-section .quiz-sub{font-size:13px;color:var(--muted);margin-bottom:24px}
.q-card{background:var(--card);border:1px solid var(--border);border-radius:14px;padding:22px;margin-bottom:14px;transition:border-color .2s}
.q-card.answered{border-color:var(--border2)}
.q-num{font-size:10px;font-weight:800;letter-spacing:1px;text-transform:uppercase;color:var(--dim);margin-bottom:8px}
.q-text{font-size:15px;font-weight:600;color:#fff;margin-bottom:16px;line-height:1.5}
.q-opts{display:grid;gap:8px}
.q-opt{display:flex;align-items:center;gap:10px;padding:10px 14px;border-radius:10px;background:var(--bg2);border:1px solid var(--border);cursor:pointer;transition:all .15s;font-size:14px;color:var(--muted);text-align:left}
.q-opt:hover:not(.disabled){background:rgba(255,255,255,.06);border-color:var(--border2);color:#fff}
.q-opt.correct{background:rgba(52,211,153,.12)!important;border-color:#34d399!important;color:#34d399!important}
.q-opt.wrong{background:rgba(248,113,113,.1)!important;border-color:#f87171!important;color:#f87171!important}
.q-opt.disabled{cursor:default;pointer-events:none}
.q-opt-letter{width:22px;height:22px;border-radius:50%;background:rgba(255,255,255,.08);display:flex;align-items:center;justify-content:center;font-size:11px;font-weight:800;flex-shrink:0}
.q-exp{margin-top:12px;padding:10px 14px;border-radius:8px;background:rgba(56,189,248,.06);border-left:3px solid var(--acc);font-size:13px;color:var(--muted);line-height:1.6;display:none}
.q-exp.show{display:block}
.q-exp strong{color:#fff}
.quiz-score{background:var(--card);border:1px solid var(--border);border-radius:14px;padding:24px;text-align:center;display:none;margin-top:16px}
.quiz-score.show{display:block}
.score-num{font-family:'Sora',sans-serif;font-size:48px;font-weight:800;color:var(--acc)}
.score-msg{font-size:14px;color:var(--muted);margin-top:6px}
.score-retry{margin-top:16px;padding:10px 24px;border-radius:50px;background:var(--acc);color:#0d1629;border:none;font-family:'DM Sans',sans-serif;font-size:14px;font-weight:800;cursor:pointer;transition:opacity .15s}
.score-retry:hover{opacity:.85}

.flash-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(200px,1fr));gap:12px;margin:16px 0 24px}
.flash{perspective:600px;height:110px;cursor:pointer;user-select:none}
.flash-inner{position:relative;width:100%;height:100%;transform-style:preserve-3d;transition:transform .45s cubic-bezier(.4,0,.2,1)}
.flash.flipped .flash-inner{transform:rotateY(180deg)}
.flash-front,.flash-back{position:absolute;inset:0;backface-visibility:hidden;border-radius:12px;display:flex;align-items:center;justify-content:center;padding:14px;text-align:center}
.flash-front{background:var(--card);border:1px solid rgba(var(--rgb),.25);font-size:13px;font-weight:700;color:#fff;line-height:1.4}
.flash-back{background:rgba(var(--rgb),.1);border:1px solid rgba(var(--rgb),.4);transform:rotateY(180deg);font-size:12px;color:var(--muted);line-height:1.55}
.flash-hint{font-size:10px;color:var(--dim);text-align:center;margin-bottom:16px}
.topic-progress{background:var(--card);border:1px solid var(--border);border-radius:12px;padding:14px 18px;margin-bottom:24px;display:flex;align-items:center;gap:14px}
.tp-label{font-size:11px;font-weight:700;color:var(--dim);text-transform:uppercase;letter-spacing:.8px;white-space:nowrap}
.tp-bar{flex:1;height:6px;background:rgba(255,255,255,.08);border-radius:50px;overflow:hidden}
/* .tp-fill and .tp-count colours are subject-specific — set in page override */

/* .eq-box and .eq-label colours are subject-specific — set in page override */
.eq-text{font-family:'Sora',sans-serif;font-size:15px;font-weight:800;color:#fff;line-height:1.5}
.eq-note{font-size:12px;color:var(--muted);margin-top:6px}
.mustkow{background:rgba(167,139,250,.06);border:1px solid rgba(167,139,250,.25);border-radius:12px;padding:16px 18px;margin:14px 0}
.mustkow-head{font-size:10px;font-weight:800;letter-spacing:1px;text-transform:uppercase;color:var(--acc);margin-bottom:10px}
.mustkow ul{padding-left:18px}
.mustkow li{font-size:14px;color:var(--muted);line-height:1.7;margin-bottom:4px}
.mustkow li strong{color:#fff}

/* nav search */
.nav-search{display:flex;align-items:center;margin-left:8px;position:relative}
.ns-icon{background:rgba(255,255,255,.07);border:1px solid rgba(255,255,255,.1);border-radius:8px;color:rgba(232,237,245,.6);cursor:pointer;padding:6px 8px;display:flex;align-items:center;transition:.15s}
.ns-icon:hover{color:#fff;background:rgba(255,255,255,.12)}
.ns-form{display:flex;align-items:center;overflow:hidden;width:0;opacity:0;transition:width .25s ease,opacity .2s;position:absolute;right:36px;top:50%;transform:translateY(-50%)}
.nav-search.open .ns-form{width:200px;opacity:1}
.ns-input{background:#0d1629;border:1.5px solid rgba(56,189,248,.4);border-radius:8px 0 0 8px;color:#e8edf5;font-size:13px;padding:6px 10px;outline:none;width:100%;font-family:inherit}
.ns-input::placeholder{color:rgba(232,237,245,.3)}
.ns-submit{background:rgba(56,189,248,.2);border:1.5px solid rgba(56,189,248,.4);border-left:none;border-radius:0 8px 8px 0;color:#38bdf8;cursor:pointer;padding:6px 10px;font-size:13px;font-family:inherit;transition:.15s}
.ns-submit:hover{background:rgba(56,189,248,.35)}
@media(max-width:500px){.nav-search.open .ns-form{width:150px}}
