:root{
  --ink:#172033; --ink-soft:#3D4A5C; --paper:#F4F6F5; --paper-card:#FBFCFB;
  --rule:#D8DEE2; --rule-strong:#B7C0C7; --tick:#1F7A4D; --tick-soft:#E6F2EC;
  --amber:#F2AE00; --amber-ink:#5B4300; --pen-red:#B23A2E;
  --shadow: 0 18px 40px -18px rgba(23,32,51,0.28);
}
*{box-sizing:border-box;}
body{margin:0; background:var(--paper); color:var(--ink); font-family:'IBM Plex Sans',sans-serif; -webkit-font-smoothing:antialiased;}
h1,h2,h3{font-family:'IBM Plex Serif',serif; margin:0; line-height:1.15; letter-spacing:-0.01em;}
a{color:inherit; text-decoration:none;}
.mono{font-family:'IBM Plex Mono',monospace;}
.wrap{max-width:1180px; margin:0 auto; padding:0 32px;}

.rebuild-banner{background:var(--ink); color:var(--paper); overflow:hidden; white-space:nowrap; border-bottom:1px solid rgba(255,255,255,0.12);}
.rebuild-banner .track{display:flex; width:max-content; animation:rebuildScroll 22s linear infinite;}
.rebuild-banner .track span{display:inline-block; padding:12px 40px; font-family:'IBM Plex Mono',monospace; font-size:16px; font-weight:600; letter-spacing:.03em; white-space:nowrap; color:var(--paper);}
@keyframes rebuildScroll{0%{transform:translateX(0);}100%{transform:translateX(-50%);}}

header.site{position:sticky; top:0; z-index:50; background:rgba(244,246,245,0.94); backdrop-filter:blur(8px); border-bottom:1px solid var(--rule);}
nav.wrap{display:flex; align-items:center; justify-content:space-between; height:76px;}
.logo{display:flex; align-items:center; gap:10px; font-family:'IBM Plex Serif',serif; font-weight:600; font-size:19px;}
.logo .mark{width:30px; height:30px; border-radius:3px; background:var(--ink); color:var(--paper); display:flex; align-items:center; justify-content:center; font-family:'IBM Plex Mono',monospace; font-size:13px; font-weight:600; transform:rotate(-4deg);}
.nav-links{display:flex; align-items:center; gap:26px; font-size:14.5px; font-weight:500; color:var(--ink-soft);}
.nav-links a:hover{color:var(--ink);}
.nav-cta{display:flex; align-items:center; gap:14px;}

.btn{display:inline-flex; align-items:center; gap:8px; padding:11px 20px; border-radius:2px; font-weight:600; font-size:14.5px; cursor:pointer; border:1.5px solid transparent; transition:transform .18s ease, box-shadow .18s ease;}
.btn-primary{background:var(--ink); color:var(--paper);}
.btn-primary:hover{transform:translateY(-2px); box-shadow:var(--shadow);}
.btn-amber{background:var(--amber); color:var(--amber-ink);}
.btn-outline{background:transparent; color:var(--ink); border-color:var(--ink-soft);}
.btn-outline:hover{border-color:var(--ink);}
.btn-block{width:100%; justify-content:center;}

main{min-height:60vh;}
.page-head{padding:56px 0 40px; border-bottom:1px solid var(--rule); background:var(--paper-card);}
.eyebrow{font-family:'IBM Plex Mono',monospace; font-size:12px; font-weight:600; letter-spacing:.08em; color:var(--tick); margin-bottom:12px;}
.page-head h1{font-size:clamp(30px,4vw,44px);}
.page-head p{margin-top:12px; color:var(--ink-soft); font-size:16px; max-width:60ch;}

section{padding:60px 0;}
.section-label{font-family:'IBM Plex Mono',monospace; font-size:12px; font-weight:600; color:var(--ink-soft); letter-spacing:.08em; text-transform:uppercase; margin-bottom:12px; display:block;}

.card-grid{display:grid; grid-template-columns:repeat(3,1fr); gap:20px;}
.tile{background:var(--paper-card); border:1px solid var(--rule); border-radius:4px; padding:26px 24px; transition:transform .2s ease, box-shadow .2s ease;}
.tile:hover{transform:translateY(-4px); box-shadow:var(--shadow);}
.tile .tag{display:inline-block; font-family:'IBM Plex Mono',monospace; font-size:11px; font-weight:600; color:var(--tick); background:var(--tick-soft); padding:3px 8px; border-radius:2px; margin-bottom:12px;}
.tile.disabled{opacity:.55;}
.tile.disabled .tag{background:var(--rule); color:var(--ink-soft);}
.tile h3{font-size:18px; margin-bottom:6px;}
.tile p{color:var(--ink-soft); font-size:14px; line-height:1.5;}

.topic-row{display:flex; align-items:center; justify-content:space-between; padding:18px 22px; background:var(--paper-card); border:1px solid var(--rule); border-radius:3px; margin-bottom:12px;}
.topic-row .name{font-weight:600; font-size:15.5px;}
.topic-row .meta{font-size:12.5px; color:var(--ink-soft); margin-top:3px;}
.lock-badge{font-family:'IBM Plex Mono',monospace; font-size:11px; font-weight:600; padding:4px 9px; border-radius:20px;}
.lock-badge.free{color:var(--tick); background:var(--tick-soft);}
.lock-badge.locked{color:var(--pen-red); border:1px solid var(--pen-red);}

.locked-banner{background:var(--ink); color:var(--paper); border-radius:4px; padding:32px 28px; text-align:center; margin:24px 0;}
.locked-banner h3{color:var(--paper); font-size:22px; margin-bottom:10px;}
.locked-banner p{color:rgba(244,246,245,0.75); margin-bottom:20px;}

.qcard{background:var(--paper-card); border:1px solid var(--rule); border-radius:4px; padding:24px; margin-bottom:18px;}
.qcard .qhead{display:flex; justify-content:space-between; font-family:'IBM Plex Mono',monospace; font-size:12px; color:var(--ink-soft); margin-bottom:12px;}
.qcard .qtext{font-family:'IBM Plex Serif',serif; font-style:italic; font-size:16px; margin-bottom:14px;}
.qcard details summary{cursor:pointer; font-weight:600; color:var(--tick); font-size:14px;}
.qcard details .sol{margin-top:12px; padding-top:12px; border-top:1px dashed var(--rule-strong); font-size:14.5px; color:var(--ink-soft); line-height:1.6;}
mjx-container{font-style:normal !important;}
.qtext table, .sol table{border-collapse:collapse; margin:12px 0; font-style:normal; width:auto;}
.qtext table th, .sol table th{background:var(--ink); color:var(--paper); padding:8px 14px; font-family:'IBM Plex Mono',monospace; font-size:12px; text-transform:uppercase; letter-spacing:.03em;}
.qtext table td, .sol table td{padding:8px 14px; border:1px solid var(--rule); font-size:14px;}
.qtext table tr:nth-child(even) td, .sol table tr:nth-child(even) td{background:var(--paper-card);}

.auth-box{max-width:420px; margin:60px auto; background:var(--paper-card); border:1px solid var(--rule); border-radius:4px; padding:36px 32px;}
.auth-box h1{font-size:26px; margin-bottom:6px;}
.auth-box p.sub{color:var(--ink-soft); font-size:14.5px; margin-bottom:24px;}
.field{margin-bottom:18px;}
.field label{display:block; font-size:13px; font-weight:600; margin-bottom:6px;}
.field input{width:100%; padding:11px 12px; border:1px solid var(--rule-strong); border-radius:3px; font-size:15px; font-family:inherit;}
.field input:focus{outline:none; border-color:var(--tick);}
.alert{padding:12px 14px; border-radius:3px; font-size:14px; margin-bottom:18px;}
.alert.error{background:#FBEAE8; color:var(--pen-red); border:1px solid rgba(178,58,46,0.3);}
.alert.success{background:var(--tick-soft); color:var(--tick); border:1px solid rgba(31,122,77,0.3);}
.auth-switch{margin-top:18px; font-size:14px; text-align:center; color:var(--ink-soft);}
.auth-switch a{color:var(--tick); font-weight:600;}

.pricing-grid{display:grid; grid-template-columns:repeat(2,1fr); gap:24px; max-width:820px; margin:0 auto;}
.plan-card{background:var(--paper-card); border:1px solid var(--rule-strong); border-radius:4px; overflow:hidden;}
.plan-card .top{padding:26px 26px 18px;}
.plan-card .name{font-family:'IBM Plex Mono',monospace; font-size:12px; letter-spacing:.06em; text-transform:uppercase; color:var(--ink-soft);}
.plan-card .price{font-family:'IBM Plex Serif',serif; font-size:28px; font-weight:600; margin-top:6px;}
.plan-card .price span{font-family:'IBM Plex Sans',sans-serif; font-size:13px; font-weight:400; color:var(--ink-soft);}
.plan-card .annual-note{margin-top:8px; font-size:12.5px; color:var(--tick);}
.plan-card ul{list-style:none; margin:16px 0; padding:0 26px;}
.plan-card li{font-size:13.5px; color:var(--ink-soft); padding-left:20px; position:relative; margin-bottom:9px;}
.plan-card li::before{content:"✓"; position:absolute; left:0; color:var(--tick); font-weight:600;}
.plan-card .bottom{padding:0 26px 26px;}

table.plain{width:100%; border-collapse:collapse; margin:20px 0;}
table.plain th, table.plain td{text-align:left; padding:10px 12px; border-bottom:1px solid var(--rule); font-size:14.5px;}
table.plain th{font-family:'IBM Plex Mono',monospace; font-size:11.5px; text-transform:uppercase; color:var(--ink-soft);}

.faq-item{border-bottom:1px solid var(--rule); padding:18px 0;}
.faq-item summary{cursor:pointer; font-weight:600; font-size:15.5px;}
.faq-item .a{margin-top:10px; color:var(--ink-soft); font-size:14.5px; line-height:1.6;}

footer.site{background:var(--paper-card); border-top:1px solid var(--rule); padding:48px 0 28px; margin-top:60px;}
.foot-bottom{display:flex; justify-content:space-between; flex-wrap:wrap; gap:16px; font-size:12.5px; color:var(--ink-soft);}
.disclaimer{max-width:680px; line-height:1.6; opacity:.85;}

@media (max-width:900px){
  .card-grid{grid-template-columns:1fr 1fr;}
  .pricing-grid{grid-template-columns:1fr;}
}
@media (max-width:640px){
  .nav-links{display:none;}
  .card-grid{grid-template-columns:1fr;}
}