:root{
  --paper:#F6F8FB; --grid:#E1E8F2; --ink:#14234B; --graphite:#4F5663; --muted:#7A8190;
  --hl:#FFE94D; --hl-soft:#FFF6B8; --ok:#1F8A5B; --ok-soft:#E3F4EC; --bad:#C93C3C; --bad-soft:#FBE7E7;
  --line:#CBD5E3; --card:#FFFFFF;
  --display:"Archivo", "Arial Narrow", sans-serif;
  --body:"Atkinson Hyperlegible Next","Atkinson Hyperlegible", system-ui, sans-serif;
}
*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{margin:0;background:var(--paper);color:var(--ink);font-family:var(--body);font-size:17px;line-height:1.55;
  background-image:linear-gradient(var(--grid) 1px,transparent 1px),linear-gradient(90deg,var(--grid) 1px,transparent 1px);
  background-size:28px 28px;background-attachment:fixed}
a{color:var(--ink)}
:focus-visible{outline:3px solid #3B6FD8;outline-offset:2px;border-radius:4px}
h1,h2,h3{font-family:var(--display);font-stretch:118%;letter-spacing:-.01em;line-height:1.05;margin:0 0 .4em}
h1{font-size:clamp(40px,5.4vw,68px);font-weight:800}
h2{font-size:clamp(28px,3.6vw,44px);font-weight:800}
h3{font-size:21px;font-weight:700}
p{margin:0 0 1em;max-width:66ch}
.wrap{max-width:1160px;margin:0 auto;padding:0 22px}
.btn{display:inline-flex;align-items:center;gap:8px;font:600 17px/1 var(--body);padding:15px 22px;border-radius:10px;border:2px solid var(--ink);
  background:var(--ink);color:#fff;text-decoration:none;cursor:pointer}
.btn:hover{background:#22356a}
.btn.ghost{background:transparent;color:var(--ink)}
.btn.ghost:hover{background:#fff}
.btn.hl{background:var(--hl);color:var(--ink);border-color:var(--ink)}
.btn.hl:hover{background:#ffe21a}
.btn.sm{padding:10px 14px;font-size:15px}
.btn[disabled]{opacity:.45;cursor:not-allowed}
.mark{background:linear-gradient(transparent 12%,var(--hl) 12%,var(--hl) 88%,transparent 88%);padding:0 .12em}

/* header */
.top{display:flex;align-items:center;justify-content:space-between;padding:18px 0}
.logo{display:flex;align-items:center;gap:10px;font:800 22px/1 var(--display);font-stretch:118%;text-decoration:none;color:var(--ink)}
.logo svg{width:34px;height:34px}
.top nav{display:flex;gap:18px;align-items:center}
.top nav a{text-decoration:none;font-weight:600;color:var(--graphite)}
.top nav a:hover{color:var(--ink)}
@media (max-width:720px){.top nav a.hide-m{display:none}}

/* hero */
.hero{display:grid;grid-template-columns:1.05fr 1fr;gap:48px;align-items:start;padding:36px 0 56px}
.hero .lede{font-size:20px;color:var(--graphite);max-width:34ch}
.hero .cta{display:flex;gap:12px;flex-wrap:wrap;margin-top:26px}
.hero .fine{margin-top:14px;color:var(--muted);font-size:15px}
@media (max-width:900px){.hero{grid-template-columns:1fr;gap:30px}}

/* question card */
.qcard{background:var(--card);border:2px solid var(--ink);border-radius:14px;box-shadow:6px 6px 0 var(--ink);padding:22px 22px 18px;position:relative}
.qmeta{font-size:14px;color:var(--muted);margin-bottom:10px;display:flex;justify-content:space-between;gap:10px}
.passage{font-size:16.5px;line-height:1.65;border-left:4px solid var(--grid);padding:2px 0 2px 14px;margin:0 0 14px}
.passage p:last-child{margin-bottom:0}
.passage table{border-collapse:collapse;margin:6px 0;font-size:15px;white-space:normal}
.passage td,.passage th{border:1px solid var(--line);padding:4px 8px}
.stem{font-weight:600;margin-bottom:14px}
.choices{display:grid;gap:10px}
.choice{display:flex;gap:12px;align-items:flex-start;text-align:left;width:100%;background:#fff;border:2px solid var(--line);border-radius:10px;padding:12px 14px;font:inherit;color:inherit;cursor:pointer}
.choice:hover{border-color:var(--ink)}
.choice .l{flex:0 0 28px;height:28px;border:2px solid var(--ink);border-radius:50%;display:grid;place-items:center;font-weight:700;font-size:14px}
.choice.sel{border-color:var(--ink);background:var(--hl-soft)}
.choice.sel .l{background:var(--ink);color:#fff}
.choice.ok{border-color:var(--ok);background:var(--ok-soft)}
.choice.ok .l{background:var(--ok);border-color:var(--ok);color:#fff}
.choice.bad{border-color:var(--bad);background:var(--bad-soft)}
.choice.bad .l{background:var(--bad);border-color:var(--bad);color:#fff}
.choice[disabled]{cursor:default}
.spr{display:flex;gap:10px}
.spr input{font:600 20px var(--body);padding:10px 12px;border:2px solid var(--ink);border-radius:10px;width:180px}
.qactions{display:flex;gap:10px;flex-wrap:wrap;margin-top:16px;align-items:center}
.verdict{font-weight:700;margin-top:14px}
.verdict.ok{color:var(--ok)} .verdict.bad{color:var(--bad)}
.explain{margin-top:10px;background:#FAFBFD;border:1px solid var(--line);border-radius:10px;padding:14px 16px;font-size:16px}
.explain p:last-child{margin-bottom:0}

/* tutor chat */
.chat{margin-top:14px;border:2px solid var(--ink);border-radius:12px;background:#fff;overflow:hidden}
.chat .head{display:flex;align-items:center;gap:8px;padding:10px 14px;background:var(--ink);color:#fff;font-weight:700}
.chat .head svg{width:22px;height:22px}
.chat .log{max-height:420px;overflow:auto;padding:12px 14px;display:grid;gap:10px}
.msg{padding:10px 12px;border-radius:10px;font-size:16px;max-width:92%}
.msg.user{background:var(--hl-soft);justify-self:end}
.msg.assistant{background:#F1F4F9}
.msg p{margin:0 0 .6em} .msg p:last-child{margin:0}
.chat form{display:flex;gap:8px;border-top:1px solid var(--line);padding:10px}
.chat input{flex:1;font:inherit;padding:10px 12px;border:1px solid var(--line);border-radius:8px}
.chips{display:flex;gap:8px;flex-wrap:wrap;padding:0 14px 10px}
.chip{font:600 14px var(--body);border:1.5px solid var(--ink);background:#fff;border-radius:999px;padding:6px 11px;cursor:pointer}
.chip:hover{background:var(--hl-soft)}

/* sections */
section{padding:56px 0}
.band{background:var(--ink);color:#fff}
.band a{color:#fff}
.dates{display:flex;gap:0;flex-wrap:wrap;border:2px solid #fff;border-radius:12px;overflow:hidden}
.dates div{flex:1 1 150px;padding:16px 18px;border-right:1px solid rgba(255,255,255,.35)}
.dates div:last-child{border-right:0}
.dates b{display:block;font:800 26px/1.1 var(--display);font-stretch:118%}
.dates small{color:#C9D3E6;font-size:14px}
.steps{display:grid;grid-template-columns:repeat(3,1fr);gap:28px;counter-reset:s}
.steps li{list-style:none;padding-top:14px;border-top:3px solid var(--ink)}
.steps li::before{counter-increment:s;content:counter(s);font:800 44px/1 var(--display);font-stretch:118%;display:block;margin-bottom:8px}
@media (max-width:820px){.steps{grid-template-columns:1fr}}
.price-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:20px;align-items:stretch}
.plan{background:#fff;border:2px solid var(--line);border-radius:14px;padding:24px;display:flex;flex-direction:column}
.plan.best{border-color:var(--ink);box-shadow:6px 6px 0 var(--ink)}
.plan .amt{font:800 46px/1 var(--display);font-stretch:118%;margin:8px 0 4px}
.plan .amt small{font:600 16px var(--body);color:var(--muted)}
.plan ul{padding-left:20px;margin:14px 0 22px;flex:1}
.plan li{margin:6px 0}
.tag{display:inline-block;background:var(--hl);border:1.5px solid var(--ink);border-radius:6px;font-size:13px;font-weight:700;padding:2px 8px}
@media (max-width:900px){.price-grid{grid-template-columns:1fr}}
.faq details{border-bottom:1px solid var(--line);padding:14px 0}
.faq summary{font-weight:700;cursor:pointer;font-size:18px}
.faq details p{margin:10px 0 0}
footer{padding:36px 0 50px;color:var(--muted);font-size:14px}
footer a{color:var(--graphite)}

/* app shell */
.shell{max-width:1160px;margin:0 auto;padding:0 18px 60px}
.apptop{display:flex;align-items:center;justify-content:space-between;padding:14px 0;gap:10px;flex-wrap:wrap}
.tabs{display:flex;gap:6px;flex-wrap:wrap}
.tabs a{text-decoration:none;font-weight:600;padding:8px 12px;border-radius:8px;color:var(--graphite)}
.tabs a.on{background:var(--ink);color:#fff}
.panel{background:#fff;border:2px solid var(--ink);border-radius:14px;padding:22px}
.grid2{display:grid;grid-template-columns:1fr 1fr;gap:20px}
@media (max-width:860px){.grid2{grid-template-columns:1fr}}
.split{display:grid;grid-template-columns:1fr 1fr;gap:0;border:2px solid var(--ink);border-radius:14px;background:#fff;overflow:hidden}
.split > div{padding:22px}
.split > div:first-child{border-right:2px solid var(--grid);max-height:78vh;overflow:auto}
.split.solo{grid-template-columns:1fr}
.split.solo > div:first-child{display:none}
@media (max-width:860px){.split{grid-template-columns:1fr}.split > div:first-child{border-right:0;border-bottom:2px solid var(--grid);max-height:none}}
.bar{height:10px;background:var(--grid);border-radius:99px;overflow:hidden}
.bar i{display:block;height:100%;background:var(--ink)}
.score{font:800 72px/1 var(--display);font-stretch:118%}
.muted{color:var(--muted)}
.row{display:flex;gap:12px;align-items:center;flex-wrap:wrap}
.skilllist{display:grid;gap:8px}
.skill{display:grid;grid-template-columns:1fr 120px 70px;gap:12px;align-items:center;padding:10px 12px;border:1px solid var(--line);border-radius:10px;background:#fff;text-decoration:none;color:inherit}
.skill:hover{border-color:var(--ink)}
@media (max-width:600px){.skill{grid-template-columns:1fr 70px}.skill .bar{display:none}}
.field{display:grid;gap:6px;margin-bottom:14px}
.field input,.field select{font:inherit;padding:12px;border:2px solid var(--line);border-radius:10px;background:#fff}
.field input:focus{border-color:var(--ink)}
.notice{background:var(--hl-soft);border:2px solid var(--ink);border-radius:12px;padding:14px 16px;margin-bottom:16px}
.err{color:var(--bad);font-weight:600}
.toast{position:fixed;bottom:18px;left:50%;transform:translateX(-50%);background:var(--ink);color:#fff;padding:12px 18px;border-radius:10px;z-index:9}
.domainhead{margin:22px 0 8px;font-weight:700}
.calc{position:fixed;right:18px;bottom:18px;width:min(520px,94vw);height:min(460px,70vh);background:#fff;border:2px solid var(--ink);border-radius:12px;box-shadow:6px 6px 0 var(--ink);z-index:8;display:flex;flex-direction:column}
.calc header{display:flex;justify-content:space-between;align-items:center;padding:6px 10px;border-bottom:1px solid var(--line);font-weight:700}
.calc iframe{flex:1;border:0;width:100%}
@media (prefers-reduced-motion:reduce){*{animation:none!important;transition:none!important}}
.choice .t p,.stem p{margin:0}
.choice .t{padding-top:2px}
.katex{font-size:1.06em}
.msg .katex-display,.explain .katex-display{margin:.5em 0;overflow-x:auto;overflow-y:hidden}
.top nav a.btn{color:#fff}
.chips{padding:10px 14px}
.log:empty{display:none}