/* Stat Exam Pro — design system. Single source of truth: tokens + chrome
   + reusable components. Pages hold only their own layout.
   Change a colour, radius, font or spacing HERE, once. */

:root{
 /* colour */
 --bg-color:#ffffff; --text-main:#1d1d1f; --text-sec:#86868b; --accent:#0071e3;
 --card-bg:#f5f5f7; --btn-bg:#1d1d1f; --btn-text:#ffffff;
 --fp:#ff9500; --fn:#ff3b30;                       /* warn / danger edges + dot colours */
 --accent-soft:rgba(0,113,227,.10); --warn-soft:rgba(255,149,0,.12); --danger-soft:rgba(255,59,48,.08);
 --hairline:rgba(134,134,139,.2); --hairline-2:rgba(134,134,139,.15);
 --gradient-1:rgba(0,113,227,.15); --gradient-2:rgba(200,0,255,.1);
 /* type */
 --font-sans:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;
 --font-mono:ui-monospace,Menlo,monospace;
 /* radius */
 --r-sm:12px; --r-md:16px; --r-lg:20px; --r-pill:999px;
 /* spacing (padding shorthands) */
 --pad-card:20px 22px; --pad-box:16px 20px;
 /* misc */
 --edge:4px;
}
@media (prefers-color-scheme: dark){ :root:not([data-theme="light"]){
 --bg-color:#000; --text-main:#fff; --text-sec:#98989D; --accent:#0A84FF;
 --card-bg:#1C1C1E; --btn-bg:#fff; --btn-text:#000; --fp:#ff9f0a; --fn:#ff453a;
 --accent-soft:rgba(10,132,255,.16); --warn-soft:rgba(255,159,10,.16); --danger-soft:rgba(255,69,58,.14);
 --gradient-1:rgba(10,132,255,.25); --gradient-2:rgba(94,92,230,.25);
}}
:root[data-theme="dark"]{
 --bg-color:#000; --text-main:#fff; --text-sec:#98989D; --accent:#0A84FF;
 --card-bg:#1C1C1E; --btn-bg:#fff; --btn-text:#000; --fp:#ff9f0a; --fn:#ff453a;
 --accent-soft:rgba(10,132,255,.16); --warn-soft:rgba(255,159,10,.16); --danger-soft:rgba(255,69,58,.14);
 --gradient-1:rgba(10,132,255,.25); --gradient-2:rgba(94,92,230,.25);
}

*{box-sizing:border-box;margin:0;padding:0}
body{font-family:var(--font-sans);background:var(--bg-color);color:var(--text-main);
 line-height:1.5;overflow-x:hidden;transition:background-color .3s ease,color .3s ease}
.container{max-width:980px;margin:0 auto;padding:0 20px;position:relative;z-index:1}
.blur-orb{position:absolute;border-radius:50%;filter:blur(80px);z-index:-1;opacity:.6}
.orb-1{top:-100px;left:-100px;width:500px;height:500px;background:var(--gradient-1)}
.orb-2{bottom:-100px;right:-100px;width:400px;height:400px;background:var(--gradient-2)}

header{padding:20px 0;display:flex;justify-content:space-between;align-items:center}
.logo{font-weight:700;font-size:1.2rem;letter-spacing:-.5px;display:flex;align-items:center;text-decoration:none;color:var(--text-main)}
.logo img{height:32px;margin-right:8px}
.header-right{display:flex;align-items:center;gap:12px}
.seg{display:flex;background:var(--card-bg);border-radius:var(--r-pill);padding:3px}
.seg a,.seg span{border:none;background:transparent;padding:5px 13px;border-radius:var(--r-pill);font-weight:600;cursor:pointer;color:var(--text-sec);font-family:inherit;font-size:.85rem;text-decoration:none;display:inline-block;line-height:1.4}
.seg .active{background:var(--btn-bg);color:var(--btn-text)}
.theme-btn{border:none;background:var(--card-bg);color:var(--text-main);width:34px;height:34px;border-radius:50%;cursor:pointer;font-size:1rem;line-height:1;flex:none}
.sitenav{display:flex;gap:8px;overflow-x:auto;padding:2px 0 10px;scrollbar-width:none}
.sitenav::-webkit-scrollbar{display:none}
.sitenav a{flex:none;background:var(--card-bg);color:var(--text-sec);padding:6px 14px;border-radius:var(--r-pill);font-size:.82rem;font-weight:600;text-decoration:none}
.sitenav a:hover{color:var(--accent)}
.sitenav a.active{background:var(--btn-bg);color:var(--btn-text)}

footer{border-top:1px solid var(--hairline);padding:36px 0;text-align:center;color:var(--text-sec);font-size:.85rem;margin-top:40px}
footer a{color:var(--text-sec);text-decoration:none;margin:0 10px}
footer a:hover{text-decoration:underline}
footer p{margin:4px 0}

/* buttons & pills */
.cta{background:var(--card-bg);border-radius:var(--r-lg);padding:var(--pad-card);margin:44px 0;display:flex;justify-content:space-between;align-items:center;gap:24px;flex-wrap:wrap}
.cta p{margin:0;flex:1 1 420px}
.btn{display:flex;align-items:center;background:var(--btn-bg);color:var(--btn-text);padding:12px 24px;border-radius:var(--r-pill);text-decoration:none;font-weight:600;font-size:.95rem;white-space:nowrap;transition:transform .2s ease}
.btn:hover{transform:scale(1.03)}
.btn svg{width:20px;height:20px;margin-right:10px;fill:currentColor}
.btn.disabled{background:var(--card-bg);color:var(--text-sec);cursor:default}
.btn.disabled:hover{transform:none}
.btn-round{width:38px;height:38px;border-radius:50%;background:var(--btn-bg);color:var(--btn-text);display:flex;align-items:center;justify-content:center;text-decoration:none;flex:none}
.apple-icon{display:inline-block;width:20px;height:20px;flex:none;background:currentColor;-webkit-mask-image:url(apple.svg);-webkit-mask-repeat:no-repeat;-webkit-mask-position:center;-webkit-mask-size:contain;mask-image:url(apple.svg);mask-repeat:no-repeat;mask-position:center;mask-size:contain}
.btn .apple-icon{margin-right:10px}
.btn-round .apple-icon{width:18px;height:18px}
.pill{display:inline-block;background:var(--btn-bg);color:var(--btn-text);padding:8px 16px;border-radius:var(--r-pill);font-size:.85rem;font-weight:600;text-decoration:none}
.pill.ghost{background:var(--bg-color);color:var(--text-main);border:1px solid var(--hairline)}
.pill.ghost:hover{color:var(--accent);border-color:var(--accent)}
.callout .pill{margin-top:10px}
.plainlink{color:inherit;text-decoration:none}
.plainlink:hover{color:var(--accent)}

/* surfaces & callouts (use on new pages; existing boxes already match via tokens) */
.card{background:var(--card-bg);border-radius:var(--r-md);padding:var(--pad-card)}
/* learn-card grid (home "two ways / learn for free", epic "three reasons") */
.grid-2{display:grid;grid-template-columns:repeat(auto-fit,minmax(280px,1fr));gap:20px}
.lcard{background:var(--card-bg);padding:26px;border-radius:var(--r-lg)}
.lcard h3{font-size:1.15rem;margin-bottom:8px;font-weight:700}
.lcard p{color:var(--text-sec);font-size:.95rem}
.lcard .fr{color:var(--accent);font-size:.85rem;margin-top:8px}
.callout{background:var(--card-bg);border-left:var(--edge) solid var(--accent);border-radius:var(--r-sm);padding:var(--pad-box);margin:16px 0}
.callout.warn{background:var(--warn-soft);border-color:var(--fp)}
.callout.danger{background:var(--danger-soft);border-color:var(--fn)}
.softbox{background:var(--accent-soft);border-radius:var(--r-sm);padding:var(--pad-box);margin:16px 0}
.chip{display:inline-block;background:var(--accent-soft);color:var(--accent);padding:6px 12px;border-radius:var(--r-pill);font-size:.8rem;font-weight:700;letter-spacing:.4px;text-decoration:none}
a.chip:hover{background:var(--accent);color:#fff}
.crumb{font-size:.85rem;color:var(--text-sec);margin:0;font-weight:600}
.crumb a{color:var(--accent);text-decoration:none}
.eyebrow{font-size:.8rem;font-weight:700;text-transform:uppercase;letter-spacing:.6px;color:var(--accent);margin-bottom:8px}

/* content primitives */
.note{color:var(--text-sec);font-size:.85rem;margin:6px 0 22px}
.calc{background:var(--card-bg);border-radius:var(--r-sm);padding:var(--pad-box);margin:16px 0;font-family:var(--font-mono);font-size:.9rem;line-height:2}
table{border-collapse:collapse;width:100%;margin:8px 0 6px;font-size:.86rem;font-variant-numeric:tabular-nums}
th,td{padding:9px 10px;text-align:right;border-bottom:1px solid var(--hairline)}
th{color:var(--text-sec);font-weight:600}
td:first-child,th:first-child{text-align:left}

/* playground: term cards (shared across calculators) */
.terms{display:grid;grid-template-columns:repeat(auto-fit,minmax(240px,1fr));gap:14px;margin:18px 0}
.term-card{background:var(--card-bg);border-radius:var(--r-md);padding:16px 18px}
.term-card h3,.term-card h4{font-size:.95rem;color:var(--accent);margin-bottom:6px;font-weight:700}
.term-card p{font-size:.92rem}
.term-card p+p{margin-top:10px}
.term-card ul{margin:8px 0 0;padding-left:18px}
.term-card li{font-size:.92rem;margin-bottom:5px}
.hook{font-size:.95rem;font-style:italic;color:var(--text-main);margin:0 0 14px;padding-left:12px;border-left:2px solid var(--accent)}

/* shared: subtitle, formula display, list card, figure */
.lead{color:var(--text-sec);font-size:1.05rem;max-width:640px}
.formula-box{background:var(--card-bg);border-radius:var(--r-md);padding:18px 16px;margin:16px 0;overflow-x:auto;text-align:center}
.list{background:var(--card-bg);border-radius:var(--r-sm);padding:6px 20px;margin:16px 0}
.list div{padding:11px 0;border-bottom:1px solid var(--hairline-2);font-size:.97rem}
.list div:last-child{border-bottom:none}
.figure{background:var(--card-bg);border-radius:var(--r-md);padding:18px 16px;margin:18px 0}
.figure svg,.figure img{width:100%;height:auto;display:block}
.train-card{background:var(--card-bg);border-radius:var(--r-lg);padding:16px 18px;display:flex;align-items:center;justify-content:space-between;gap:14px;font-size:.9rem;color:var(--text-sec);font-weight:600}

/* two-up figure rows (lesson-format pages: figure pairs, widget rows) */
.figrow{display:grid;grid-template-columns:1fr 1fr;gap:20px;align-items:center;margin:22px 0}
.figcap{background:var(--card-bg);border-radius:var(--r-md);padding:18px 20px;font-size:.9rem;color:var(--text-sec)}
.figcol{display:flex;flex-direction:column;gap:18px}
.figrow .note{margin:0}
.figrow .figure{margin:0}
.wrow{align-items:stretch}
.wrow .figure{display:flex;flex-direction:column;justify-content:center}
.wnote{margin:-2px 0 22px}
@media(max-width:700px){.figrow{grid-template-columns:1fr}}

/* page h1 (playgrounds & lesson use as-is; landing/fails/studies override size/margin locally) */
h1{font-size:2.1rem;font-weight:800;letter-spacing:-1px;margin:24px 0 10px}
.story-title{font-size:2rem;margin:0 0 12px}          /* Stat Fails story headline (shared by the 4 story pages) */
@media(max-width:600px){.story-title{font-size:1.6rem}}

/* playground kit (ppv / nnt / roc): control panel, presets, readouts, lesson blocks */
.play{display:grid;grid-template-columns:340px 1fr;gap:28px;align-items:start}   /* pages add their own margin */
@media(max-width:820px){.play{grid-template-columns:1fr}}
.legend{display:flex;gap:16px;flex-wrap:wrap;font-size:.8rem;color:var(--text-sec)}
.legend span{display:flex;align-items:center;gap:6px}
.panel{background:var(--card-bg);border-radius:var(--r-lg);padding:22px}
.ctrl{margin-bottom:18px}
.ctrl label{display:flex;justify-content:space-between;font-size:.9rem;font-weight:600;margin-bottom:6px}
.ctrl label .val{color:var(--accent);font-variant-numeric:tabular-nums}
input[type=range]{width:100%;accent-color:var(--accent)}
.presets{display:flex;gap:8px;flex-wrap:wrap;margin:4px 0 18px}
.preset{border:none;background:var(--bg-color);color:var(--text-main);border-radius:var(--r-md);padding:6px 12px;font-size:.8rem;font-weight:600;cursor:pointer;font-family:inherit}
.preset:hover{color:var(--accent)}
.bignum{font-size:2.6rem;font-weight:800;letter-spacing:-1px;color:var(--accent);font-variant-numeric:tabular-nums;line-height:1.1}
.bignum-label{font-size:.85rem;color:var(--text-sec);margin-bottom:14px}
.smallnum{font-size:1.02rem;font-weight:700;font-variant-numeric:tabular-nums;color:var(--text-sec);margin-top:8px}
.sentence{background:var(--card-bg);border-left:var(--edge) solid var(--accent);border-radius:var(--r-sm);padding:18px 20px;font-size:1.02rem}
.interpret{display:flex;gap:14px;align-items:flex-start;font-size:1rem}
.interpret .emoji{font-size:1.7rem;line-height:1.1;flex:none}
.howto{background:var(--card-bg);border-radius:var(--r-sm);padding:16px 20px;margin:14px 0}
.howto p{font-size:.95rem;margin:0}
.bridge{font-size:1.02rem;margin:26px 0 12px}
.lesson,.worked,.faq{margin:40px 0}
.lesson h2,.worked h2,.faq h2{font-size:1.5rem;font-weight:800;letter-spacing:-.5px;margin-bottom:12px}
.lesson p,.worked p{margin-bottom:14px}
.problem{font-size:1.02rem}
.answer{font-weight:600}
.faq details{border-top:1px solid var(--hairline)}
.faq details:last-of-type{border-bottom:1px solid var(--hairline)}
.faq summary{cursor:pointer;font-weight:700;font-size:1.05rem;padding:16px 0;list-style:none;display:flex;justify-content:space-between;align-items:center;gap:14px}
.faq summary::-webkit-details-marker{display:none}
.faq summary::after{content:"+";color:var(--accent);font-size:1.3rem;font-weight:700;flex:none;line-height:1}
.faq details[open] summary::after{content:"\2212"}
.faq p{margin:0 0 16px;color:var(--text-sec)}

/* article kit (Stat Fails): chip row, numbers, quotes, takeaways, sources */
.chip-row{display:flex;justify-content:space-between;align-items:center;gap:14px;margin:20px 0 14px;flex-wrap:wrap}
.train{display:flex;align-items:center;gap:10px;font-size:.85rem;color:var(--text-sec);font-weight:600}
.rubric{color:var(--text-sec);font-size:.95rem;margin-bottom:26px;max-width:640px}
article h2{font-size:1.4rem;font-weight:800;letter-spacing:-.4px;margin:34px 0 10px}
article p{margin-bottom:16px;font-size:1.02rem}
.quote{font-size:1.08rem;font-style:italic}
.pull .big{font-size:1.15rem;font-weight:700;font-style:italic}
.who{color:var(--text-sec);font-size:.85rem;margin-top:6px;font-style:normal}
.nums{display:grid;grid-template-columns:repeat(auto-fit,minmax(170px,1fr));gap:12px;margin:18px 0}
.num{background:var(--card-bg);border-radius:var(--r-md);padding:16px}
.num b{display:block;font-size:1.5rem;font-weight:800;letter-spacing:-.5px;margin-bottom:4px}
.num span{color:var(--text-sec);font-size:.85rem;line-height:1.4}
.num.hero{background:var(--accent)}
.num.hero b{color:#fff}
.num.hero span{color:rgba(255,255,255,.85)}
/* stat-readout tile variants (centred, tabular numbers, tight label): nnt + screening */
.num.stat{text-align:center;padding:12px 10px}
.num.stat b{margin-bottom:0;line-height:1.1;font-variant-numeric:tabular-nums}
.num.stat span{display:block;font-size:.72rem;line-height:1.25;margin:3px 0 0}
.num.stat.plain{background:var(--bg-color)}   /* tile the colour of the page, not the card */
.num.stat.accent b{color:var(--accent)}       /* accent-coloured number */
.num.stat.sm{border-radius:var(--r-sm);padding:12px 8px}
.num.stat.sm b{letter-spacing:0}
.mech{font-weight:600}
.invite p{margin:0 0 14px}
.takeaway{background:var(--card-bg);border-radius:var(--r-sm);padding:16px 20px;margin:18px 0}
.takeaway p{margin:0}
.sources{margin:34px 0 0}
.sources h2{font-size:1rem;font-weight:700;margin-bottom:10px}
.sources li{font-size:.88rem;color:var(--text-sec);margin-bottom:8px;margin-left:18px}
.sources a{color:var(--accent);text-decoration:none}
.dive h2{font-size:1.5rem;font-weight:800;letter-spacing:-.5px;margin:40px 0 8px}
.dive h3{font-size:1.15rem;font-weight:700;margin:28px 0 8px}
.dive>p{margin-bottom:14px}

/* ===== course rail: primary navigation (injected at build time) =====
   Full-width sticky top bar + a filled left rail that is the whole course, topic-grouped,
   current lesson highlighted. Collapses on desktop (remembered) and becomes a drawer on
   phones, both driven by the #burger toggle. The landing page and 404 opt out. */
.blur-orb{position:fixed}
.top{display:block;padding:0;position:sticky;top:0;z-index:30;background:color-mix(in srgb,var(--bg-color) 82%,transparent);backdrop-filter:blur(14px);border-bottom:1px solid var(--hairline-2)}
.top-in{max-width:1200px;margin:0 auto;padding:11px 20px;display:flex;align-items:center;gap:14px}
.top .logo{flex:none}
.top .spacer{flex:1}
.burger{display:grid;place-items:center}
.shell{max-width:1200px;margin:0 auto;padding:0 20px;display:grid;grid-template-columns:262px 1fr;gap:36px;position:relative;z-index:1}
.coursenav{position:sticky;top:60px;align-self:start;height:calc(100vh - 76px);overflow-y:auto;scrollbar-width:thin;background:var(--card-bg);border-radius:var(--r-lg);padding:16px 12px 30px}
.coursenav::-webkit-scrollbar{width:7px}
.coursenav::-webkit-scrollbar-thumb{background:var(--hairline);border-radius:99px}
.coursenav ul{list-style:none;margin:0;padding:0}
.cn-grp{margin:0 0 16px}
.cn-grp>h4{font-size:.72rem;font-weight:700;letter-spacing:.09em;text-transform:uppercase;color:var(--text-sec);padding:0 10px;margin:6px 0 6px;display:flex;gap:7px}
.cn-grp>h4 .cn-n{color:var(--accent);font-variant-numeric:tabular-nums}
.coursenav a{display:flex;align-items:center;gap:10px;padding:7px 10px;border-radius:10px;text-decoration:none;color:var(--text-main);font-size:.9rem;line-height:1.3}
.coursenav a .cn-ic{width:18px;height:18px;flex:none;color:var(--text-sec)}
.coursenav a .cn-ic svg{width:18px;height:18px;display:block}
.coursenav a .cn-lb{min-width:0;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}
.coursenav a:hover{background:var(--bg-color)}
.coursenav a:hover .cn-ic{color:var(--accent)}
.coursenav a.cn-on{background:var(--accent);color:#fff}
.coursenav a.cn-on .cn-ic{color:#fff}
.coursenav a.cn-soon{color:var(--text-sec);opacity:.6;pointer-events:none}
.cn-tag{font-size:.6rem;font-weight:700;letter-spacing:.06em;text-transform:uppercase;color:var(--text-sec);background:var(--bg-color);padding:2px 6px;border-radius:99px;margin-left:auto}
.main{padding:24px 0 60px;min-width:0}
.scrim{display:none;position:fixed;inset:0;background:rgba(0,0,0,.4);z-index:25}
@media(min-width:901px){
 body.nav-collapsed .shell{grid-template-columns:1fr}
 body.nav-collapsed .coursenav{display:none}
 body.nav-collapsed .main{max-width:820px;margin:0 auto}
 body.home.nav-collapsed .main{max-width:960px}   /* landing keeps its fuller width when the rail is tucked away */
}
@media(max-width:900px){
 .shell{grid-template-columns:1fr;gap:0;z-index:auto}   /* drop the stacking context so the fixed drawer (z 28) rises above the scrim (z 25) and stays tappable */
 .coursenav{position:fixed;top:0;left:0;z-index:28;height:100vh;width:290px;max-width:86vw;border-radius:0;transform:translateX(-100%);transition:transform .26s ease;box-shadow:0 0 40px rgba(0,0,0,.18)}
 body.nav-open .coursenav{transform:none}
 body.nav-open .scrim{display:block}
 .main{padding:20px 0 50px}
}
@media(max-width:560px){
 .top .logo span{display:none}   /* phones: logo mark only, so the top bar can't crowd the round buttons into ovals */
}