:root{
  --bg-primary:#0f172a; --bg-card:rgba(30,41,59,.55); --bg-card-solid:#1e293b; --border-color:rgba(255,255,255,.1);
  --text-primary:#f1f5f9; --text-secondary:#94a3b8; --emerald:#10b981; --indigo:#6366f1; --pink:#ec4899; --amber:#f59e0b; --cyan:#06b6d4; --red:#ef4444;
  --emerald-text:#10b981; --emerald-solid:#047857; --indigo-solid:#4f46e5;
  --input-bg:rgba(15,23,42,.6); --shadow:0 8px 32px rgba(0,0,0,.35);
}
html.light{
  --bg-primary:#f8fafc; --bg-card:rgba(255,255,255,.75); --bg-card-solid:#ffffff; --border-color:rgba(15,23,42,.08);
  --text-primary:#0f172a; --text-secondary:#475569; --input-bg:rgba(241,245,249,.9); --shadow:0 8px 24px rgba(15,23,42,.08);
  --emerald-text:#047857;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{font-family:'Inter',sans-serif;background:var(--bg-primary);color:var(--text-primary);transition:background .25s,color .25s,margin-left .2s ease;margin:0;line-height:1.6}
.mono{font-family:'JetBrains Mono',monospace}
.glass{background:var(--bg-card);border:1px solid var(--border-color);border-radius:1rem;backdrop-filter:blur(14px);-webkit-backdrop-filter:blur(14px);box-shadow:var(--shadow)}
::-webkit-scrollbar{width:8px;height:8px}
::-webkit-scrollbar-thumb{background:var(--border-color);border-radius:4px}
.accent-text{color:var(--emerald-text)}
a{color:inherit}
.wrap{max-width:1100px;margin:0 auto;padding:0 1rem}
.wrap-narrow{max-width:760px;margin:0 auto;padding:0 1rem}

/* ============ left sidebar navigation ============ */
body{margin-left:0}
#siteHeader{position:fixed;top:0;left:0;height:100vh;width:264px;background:var(--bg-card-solid);border-right:1px solid var(--border-color);z-index:100;display:flex;flex-direction:column;transform:translateX(-100%);transition:transform .25s ease,width .2s ease}
#siteHeader.open{transform:translateX(0)}
@media(min-width:900px){
  body{margin-left:264px}
  #siteHeader{transform:translateX(0)}
}
.sidebar-top{padding:1.1rem 1rem .9rem;display:flex;align-items:center;justify-content:space-between;gap:.5rem;border-bottom:1px solid var(--border-color);flex-shrink:0}
.sidebar-scroll{flex:1;overflow-y:auto;padding:.75rem}
.sidebar-bottom{padding:.85rem 1rem;border-top:1px solid var(--border-color);display:flex;gap:.5rem;align-items:center;flex-shrink:0}
.brand{display:flex;align-items:center;gap:.5rem;font-weight:800;font-size:1.05rem;letter-spacing:-.01em;text-decoration:none;color:var(--text-primary);min-width:0}
.brand svg{flex-shrink:0}
.icon-btn{background:var(--input-bg);border:1px solid var(--border-color);border-radius:.5rem;width:2.25rem;height:2.25rem;display:flex;align-items:center;justify-content:center;cursor:pointer;transition:.15s;flex-shrink:0}
.icon-btn:hover{border-color:var(--emerald-text)}
.side-nav-links{display:flex;flex-direction:column;gap:.25rem;margin-bottom:1rem}
.side-link{display:flex;align-items:center;gap:.55rem;padding:.5rem .6rem;border-radius:.5rem;text-decoration:none;color:var(--text-primary);font-size:.87rem;font-weight:600;transition:background .12s}
.side-link:hover{background:var(--input-bg)}
.side-link.active{background:rgba(16,185,129,.15);color:var(--emerald-text)}
.side-link i{width:16px;text-align:center;flex-shrink:0}
.lang-select{background:var(--input-bg);border:1px solid var(--border-color);color:var(--text-primary);border-radius:.5rem;padding:.4rem .5rem;font-size:.78rem;width:100%;cursor:pointer}
.sidebar-toggle-btn{position:fixed;top:.75rem;left:.75rem;z-index:110;width:2.5rem;height:2.5rem;border-radius:.6rem;background:var(--bg-card-solid);border:1px solid var(--border-color);display:flex;align-items:center;justify-content:center;cursor:pointer;box-shadow:var(--shadow)}
@media(min-width:900px){.sidebar-toggle-btn{display:none}}
#sidebarOverlay{position:fixed;inset:0;background:rgba(0,0,0,.5);z-index:95;display:none}
#sidebarOverlay.show{display:block}
@media(min-width:900px){#sidebarOverlay{display:none!important}}

/* desktop collapsible sidebar */
.collapse-btn{display:none;flex-shrink:0}
@media(min-width:900px){.collapse-btn{display:flex}}
@media(min-width:900px){body.sidebar-collapsed{margin-left:72px}}
body.sidebar-collapsed #readProgress{transition:left .2s ease}
@media(min-width:900px){body.sidebar-collapsed #readProgress{left:72px}}
#siteHeader.collapsed{width:72px}
#siteHeader.collapsed .sidebar-top{justify-content:center;padding-left:.5rem;padding-right:.5rem}
#siteHeader.collapsed .brand{justify-content:center;width:auto}
#siteHeader.collapsed .brand-text,
#siteHeader.collapsed .side-link .label,
#siteHeader.collapsed .progress-pill,
#siteHeader.collapsed .progress-track,
#siteHeader.collapsed .menu-stage,
#siteHeader.collapsed .lang-select{display:none}
#siteHeader.collapsed .side-link{justify-content:center}
#siteHeader.collapsed .sidebar-bottom{flex-direction:column}

/* ad placeholder — hidden entirely unless AdSense is configured */
.ad-slot{min-height:90px;display:flex;align-items:center;justify-content:center;border:1px dashed var(--border-color);border-radius:.75rem;color:var(--text-secondary);font-size:.72rem;margin:0 0 1.5rem;text-transform:uppercase;letter-spacing:.04em}
.ad-slot.hidden{display:none}

/* progress bar (reading progress on lesson pages) */
#readProgress{position:fixed;top:0;left:0;height:3px;background:linear-gradient(90deg,var(--emerald),var(--indigo));z-index:105;width:0%;transition:width .1s linear}
@media(min-width:900px){#readProgress{left:264px}}

/* hero */
.hero{padding:3rem 0 2rem}
.hero h1{font-size:clamp(1.8rem,4vw,2.75rem);font-weight:800;letter-spacing:-.02em;margin:0 0 .75rem}
.hero p.lead{color:var(--text-secondary);font-size:1.05rem;max-width:640px}

/* stage timeline on hub page */
.stage{margin:2.5rem 0}
.stage-head{display:flex;align-items:center;gap:.75rem;margin-bottom:1rem}
.stage-num{width:2.5rem;height:2.5rem;border-radius:50%;display:flex;align-items:center;justify-content:center;font-weight:800;font-size:1rem;color:#fff;flex-shrink:0}
.stage-head h2{font-size:1.3rem;font-weight:800;margin:0}
.stage-head .age-range{color:var(--text-secondary);font-size:.85rem;font-weight:600}
.module-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(260px,1fr));gap:1.15rem}
.module-card{display:block;text-decoration:none;color:inherit;padding:1.4rem 1.25rem 1.25rem;position:relative;overflow:hidden;border-radius:1.25rem!important;transition:transform .18s ease,border-color .15s,box-shadow .18s ease;--accent:var(--emerald-text)}
.module-card::before{content:'';position:absolute;top:0;left:0;right:0;height:4px;background:var(--accent);border-radius:1.25rem 1.25rem 0 0}
.module-card:hover{transform:translateY(-4px);border-color:var(--accent);box-shadow:0 16px 32px -16px var(--accent)}
.module-card .m-icon{width:2.9rem;height:2.9rem;border-radius:50%;display:flex;align-items:center;justify-content:center;font-size:1.15rem;color:#fff;margin-bottom:.9rem;box-shadow:0 6px 16px -6px var(--accent);transition:transform .18s ease}
.module-card:hover .m-icon{transform:scale(1.08) rotate(-4deg)}
.module-card h3{font-size:1.02rem;font-weight:700;margin:0 0 .35rem}
.module-card p{font-size:.85rem;color:var(--text-secondary);margin:0}
.module-card .check{position:absolute;top:1.1rem;right:1.1rem;color:var(--emerald-text);font-size:1.1rem;display:none}
.module-card.done .check{display:block}
.module-card.done{border-color:var(--emerald-text)}

/* article layout */
.lesson-layout{display:grid;grid-template-columns:1fr;gap:2rem;padding:2rem 0 4rem}
@media(min-width:900px){.lesson-layout{grid-template-columns:200px minmax(0,1fr)}}
.toc{position:sticky;top:5rem;align-self:start;display:none}
@media(min-width:900px){.toc{display:block}}
.toc h4{font-size:.7rem;text-transform:uppercase;letter-spacing:.06em;color:var(--text-secondary);margin:0 0 .6rem;font-weight:700}
.toc a{display:block;font-size:.82rem;color:var(--text-secondary);text-decoration:none;padding:.3rem 0 .3rem .6rem;border-left:2px solid var(--border-color);transition:.15s}
.toc a:hover,.toc a.active{color:var(--emerald-text);border-left-color:var(--emerald-text)}

article.lesson h2{font-size:1.5rem;font-weight:800;margin:2.25rem 0 .9rem;scroll-margin-top:5rem;letter-spacing:-.01em}
article.lesson h2:first-of-type{margin-top:0}
article.lesson h3{font-size:1.1rem;font-weight:700;margin:1.5rem 0 .6rem}
article.lesson p{margin:0 0 1rem;color:var(--text-primary)}
article.lesson ul,article.lesson ol{margin:0 0 1rem;padding-left:1.3rem}
article.lesson li{margin-bottom:.4rem}
article.lesson strong{color:var(--emerald-text)}
.lede{font-size:1.1rem;color:var(--text-secondary);margin-bottom:1.5rem!important}

.callout{border-radius:.85rem;border:1px solid;padding:1rem 1.15rem;margin:1.25rem 0;font-size:.92rem}
.callout-tip{background:rgba(16,185,129,.1);border-color:rgba(16,185,129,.35)}
.callout-warn{background:rgba(245,158,11,.1);border-color:rgba(245,158,11,.35)}
.callout-example{background:rgba(99,102,241,.1);border-color:rgba(99,102,241,.35)}
.callout b.label{display:flex;align-items:center;gap:.4rem;margin-bottom:.35rem;font-size:.75rem;text-transform:uppercase;letter-spacing:.05em}
.callout-tip b.label{color:var(--emerald-text)}
.callout-warn b.label{color:var(--amber)}
.callout-example b.label{color:var(--indigo)}

.diagram{background:var(--input-bg);border:1px solid var(--border-color);border-radius:1rem;padding:1.25rem;margin:1.5rem 0;overflow-x:auto}
.diagram svg{display:block;margin:0 auto;max-width:100%;height:auto}
.diagram figcaption{text-align:center;font-size:.78rem;color:var(--text-secondary);margin-top:.6rem}

.compare-grid{display:grid;grid-template-columns:1fr;gap:1rem;margin:1.25rem 0}
@media(min-width:640px){.compare-grid{grid-template-columns:repeat(var(--cols,2),1fr)}}
.compare-card{border:1px solid var(--border-color);border-radius:.85rem;padding:1.1rem;background:var(--input-bg)}
.compare-card h4{margin:0 0 .5rem;font-size:.95rem;font-weight:700;display:flex;align-items:center;gap:.5rem}
.compare-card ul{margin:0;padding-left:1.1rem;font-size:.85rem}
.compare-card li{margin-bottom:.3rem}

.calc-link{display:inline-flex;align-items:center;gap:.5rem;background:var(--emerald-solid);color:#fff!important;text-decoration:none;padding:.6rem 1rem;border-radius:.6rem;font-size:.88rem;font-weight:600;margin:.3rem .5rem .3rem 0;transition:background .15s}
.calc-link:hover{background:#065f46}

.key-takeaways{background:var(--bg-card);border:1px solid var(--border-color);border-radius:1rem;padding:1.5rem;margin:2rem 0}
.key-takeaways h3{margin-top:0;display:flex;align-items:center;gap:.5rem;color:var(--emerald-text)}
.key-takeaways ul{margin:0;padding-left:1.2rem}

.lesson-nav{display:flex;justify-content:space-between;gap:1rem;margin-top:2.5rem;padding-top:1.5rem;border-top:1px solid var(--border-color)}
.lesson-nav a{flex:1;text-decoration:none;color:inherit;border:1px solid var(--border-color);border-radius:.75rem;padding:1rem;transition:.15s}
.lesson-nav a:hover{border-color:var(--emerald-text)}
.lesson-nav .dir{font-size:.7rem;text-transform:uppercase;color:var(--text-secondary);letter-spacing:.05em;display:block;margin-bottom:.25rem}
.lesson-nav .next{text-align:right}

.complete-btn{display:inline-flex;align-items:center;gap:.5rem;border:1px solid var(--emerald-text);color:var(--emerald-text);background:transparent;border-radius:.6rem;padding:.6rem 1.1rem;font-size:.88rem;font-weight:700;cursor:pointer;transition:.15s}
.complete-btn.done,.complete-btn:hover{background:var(--emerald-solid);color:#fff}

.breadcrumb{font-size:.8rem;color:var(--text-secondary);margin-bottom:1rem}
.breadcrumb a{color:var(--text-secondary);text-decoration:none}
.breadcrumb a:hover{color:var(--emerald-text)}

#siteFooter{border-top:1px solid var(--border-color);margin-top:3rem;padding:2rem 1rem;text-align:center;font-size:.8rem;color:var(--text-secondary)}
#siteFooter a{color:var(--text-secondary);text-decoration:underline}
#siteFooter p{max-width:640px;margin-left:auto;margin-right:auto}

.progress-summary{display:flex;align-items:center;gap:.75rem;margin:1.5rem 0}
.progress-track{flex:1;height:.5rem;border-radius:9999px;background:var(--border-color);overflow:hidden}
.progress-fill{height:100%;background:linear-gradient(90deg,var(--emerald),var(--indigo));border-radius:9999px;transition:width .3s}

.continue-card{display:flex;align-items:center;gap:1rem;text-decoration:none;color:inherit;background:var(--bg-card);border:1px solid var(--border-color);border-left:4px solid var(--emerald-text);border-radius:1rem;padding:1.1rem 1.25rem;margin:1.5rem 0 0;transition:transform .15s ease,box-shadow .15s ease}
.continue-card:hover{transform:translateY(-2px);box-shadow:0 12px 28px -16px rgba(16,185,129,.5)}
.continue-card .continue-icon{width:2.5rem;height:2.5rem;border-radius:50%;background:var(--emerald-solid);color:#fff;display:flex;align-items:center;justify-content:center;flex-shrink:0;font-size:.85rem}
.continue-card .continue-label{display:block;font-size:.72rem;text-transform:uppercase;letter-spacing:.05em;color:var(--text-secondary);margin-bottom:.15rem}
.continue-card strong{font-size:.95rem}
.continue-card > i:last-child{margin-left:auto;color:var(--text-secondary);flex-shrink:0}

/* curriculum list, inline in the sidebar */
.menu-stage{margin-bottom:.35rem}
.menu-stage h5{font-size:.66rem;text-transform:uppercase;letter-spacing:.05em;font-weight:800;margin:.9rem .5rem .3rem;opacity:.75}
.menu-item{display:flex;align-items:center;gap:.55rem;padding:.4rem .5rem;border-radius:.5rem;text-decoration:none;color:var(--text-primary);font-size:.82rem;transition:background .1s}
.menu-item:hover{background:var(--input-bg)}
.menu-item.current{background:rgba(16,185,129,.15);font-weight:700;color:var(--emerald-text)}
.menu-item i{width:16px;text-align:center;font-size:.78rem;color:var(--text-secondary);flex-shrink:0}
.menu-item.current i{color:var(--emerald-text)}
.menu-item .done-check{color:var(--emerald-text)}
.progress-pill{font-size:.72rem;font-weight:700;color:var(--text-secondary);margin:0 0 .75rem;display:block}

/* byline */
.lesson-byline{display:flex;align-items:center;gap:.5rem;font-size:.78rem;color:var(--text-secondary);margin:-.75rem 0 1.5rem;flex-wrap:wrap}
.lesson-byline .avatar{width:22px;height:22px;border-radius:50%;background:var(--emerald-solid);color:#fff;display:flex;align-items:center;justify-content:center;font-size:.65rem;font-weight:800}

/* quiz */
.quiz-block{margin:2.5rem 0}
.quiz-block > h2{margin-bottom:.25rem!important}
.quiz-intro{color:var(--text-secondary);font-size:.9rem;margin:0 0 1.25rem}
.quiz-q{border:1px solid var(--border-color);border-radius:.85rem;padding:1.1rem;margin-bottom:1rem;background:var(--bg-card)}
.quiz-question{font-weight:700;margin:0 0 .8rem;font-size:.95rem}
.quiz-choices{display:flex;flex-direction:column;gap:.5rem}
.quiz-choice{text-align:left;padding:.65rem .9rem;border-radius:.6rem;border:1px solid var(--border-color);background:var(--input-bg);color:var(--text-primary);font-size:.87rem;cursor:pointer;transition:.12s;font-family:inherit}
.quiz-choice:hover:not(:disabled){border-color:var(--emerald-text)}
.quiz-choice:disabled{cursor:default}
.quiz-choice.correct{border-color:var(--emerald-text);background:rgba(16,185,129,.15);color:var(--emerald-text);font-weight:700}
.quiz-choice.incorrect{border-color:#ef4444;background:rgba(239,68,68,.12);color:#ef4444}
.quiz-feedback{margin:.75rem 0 0;font-size:.85rem;padding:.6rem .8rem;border-radius:.5rem}
.quiz-feedback.is-correct{background:rgba(16,185,129,.1);color:var(--emerald-text)}
.quiz-feedback.is-incorrect{background:rgba(239,68,68,.1);color:#ef4444}
.quiz-score{margin-top:1rem;padding:1rem;border-radius:.75rem;background:var(--bg-card);border:1px solid var(--border-color);font-weight:700;text-align:center}

/* action steps */
.action-steps{margin:2rem 0;background:var(--bg-card);border:1px solid var(--border-color);border-radius:1rem;padding:1.5rem}
.action-steps h3{margin-top:0;display:flex;align-items:center;gap:.5rem;color:var(--indigo)}
.action-steps p.action-intro{font-size:.85rem;color:var(--text-secondary);margin:0 0 1rem}
.action-item{display:flex;align-items:flex-start;gap:.65rem;padding:.6rem 0;border-bottom:1px solid var(--border-color)}
.action-item:last-child{border-bottom:none}
.action-item input[type=checkbox]{margin-top:.2rem;width:18px;height:18px;accent-color:var(--emerald-solid);cursor:pointer;flex-shrink:0}
.action-item label{font-size:.9rem;cursor:pointer}
.action-item.done label{color:var(--text-secondary);text-decoration:line-through}

.about-note{background:var(--bg-card);border:1px solid var(--border-color);border-radius:1rem;padding:1.5rem;margin:2rem 0;font-size:.92rem}
.about-note p:last-child{margin-bottom:0}

/* kudos toast — shown when a lesson is marked complete */
.kudos-toast{position:fixed;bottom:1.25rem;right:1.25rem;max-width:320px;background:var(--bg-card-solid);border:1px solid var(--emerald-text);border-radius:1rem;box-shadow:var(--shadow);padding:1rem 1.15rem;display:flex;gap:.75rem;align-items:flex-start;z-index:200;transform:translateY(16px) scale(.97);opacity:0;pointer-events:none;transition:transform .3s cubic-bezier(.34,1.56,.64,1),opacity .25s ease}
.kudos-toast.show{transform:translateY(0) scale(1);opacity:1;pointer-events:auto}
.kudos-toast .kudos-icon{font-size:1.6rem;color:var(--emerald-text);flex-shrink:0;margin-top:.1rem}
.kudos-toast h4{margin:0 0 .2rem;font-size:.92rem;font-weight:800}
.kudos-toast p{margin:0;font-size:.8rem;color:var(--text-secondary)}
@media(max-width:600px){.kudos-toast{left:1rem;right:1rem;max-width:none;bottom:1rem}}

/* top nav-loading indicator — instant feedback on internal link clicks */
#navLoadingBar{position:fixed;top:0;left:0;height:3px;width:0;background:linear-gradient(90deg,var(--emerald),var(--indigo));z-index:300;transition:width .3s ease,opacity .2s ease;opacity:0;pointer-events:none}
#navLoadingBar.active{opacity:1;width:75%}