@font-face{font-family:"Work Sans";font-weight:400;font-display:swap;src:url(/assets/fonts/worksans-regular.woff2) format("woff2")}
@font-face{font-family:"Work Sans";font-weight:600;font-display:swap;src:url(/assets/fonts/worksans-semibold.woff2) format("woff2")}
@font-face{font-family:"Work Sans";font-weight:700;font-display:swap;src:url(/assets/fonts/worksans-bold.woff2) format("woff2")}
@font-face{font-family:"Work Sans";font-weight:900;font-display:swap;src:url(/assets/fonts/worksans-black.woff2) format("woff2")}

:root{
  --paper:#F3EFE6; --paper-2:#E9E3D6; --ink:#141414; --ink-2:#4a4741; --line:#d6cfbf;
  --red:#D7263D; --white:#fff;
  --accent:#D7263D;
  --radius:4px;
}
*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%;scroll-behavior:smooth}
body{margin:0;background:var(--paper);color:var(--ink);font:400 17px/1.55 "Work Sans",system-ui,-apple-system,"Segoe UI",sans-serif}
img{max-width:100%;height:auto;display:block}
a{color:inherit}
h1,h2,h3{font-weight:900;line-height:1.05;letter-spacing:-.01em;margin:0 0 .5em}
h1{font-size:clamp(2.4rem,8vw,4.6rem);text-transform:uppercase}
h2{font-size:clamp(1.6rem,4.5vw,2.4rem);text-transform:uppercase}
h3{font-size:1.2rem}
p{margin:0 0 1em}
.wrap{max-width:1080px;margin:0 auto;padding:0 16px}
.skip{position:absolute;left:-999px}.skip:focus{left:8px;top:8px;background:var(--ink);color:var(--paper);padding:8px 12px;z-index:9}
.small{font-size:.82rem;color:var(--ink-2)}
.sub{color:var(--ink-2);max-width:60ch}

/* header */
.top{border-bottom:2px solid var(--ink);background:var(--paper);position:sticky;top:0;z-index:5}
.top-in{display:flex;align-items:center;justify-content:space-between;gap:16px;min-height:64px}
.brand{display:flex;align-items:center;gap:10px;text-decoration:none}
.mark{display:grid;grid-template-columns:repeat(3,10px);gap:2px}
.mark i{width:10px;height:10px;background:var(--ink)}
.mark i:nth-child(3){background:var(--red)}
.word{display:flex;flex-direction:column;line-height:1}
.word b{font-weight:900;font-size:1.18rem;letter-spacing:.02em}
.word small{font-weight:600;font-size:.62rem;letter-spacing:.27em}
.nav{display:flex;gap:18px;font-weight:700;font-size:.95rem}
.nav a{text-decoration:none}
.nav a:hover,.nav a:focus{text-decoration:underline;text-underline-offset:4px}
@media (max-width:520px){.nav{gap:12px;font-size:.85rem}.word small{display:none}}

/* buttons */
.btn{display:inline-block;background:var(--ink);color:var(--paper);font-weight:700;text-decoration:none;padding:.75em 1.2em;border:2px solid var(--ink);border-radius:var(--radius);margin:0 .4em .5em 0}
.btn:hover,.btn:focus{background:var(--accent);border-color:var(--accent);color:var(--ink)}
.btn-ghost{background:transparent;color:var(--ink)}
.btn[aria-disabled=true]{opacity:.55;pointer-events:none}

/* hero */
.hero{padding:48px 0 40px;border-bottom:2px solid var(--ink)}
.hero-in{display:grid;gap:32px;align-items:center}
@media (min-width:860px){.hero-in{grid-template-columns:1.2fr .8fr}}
.kicker{font-weight:700;letter-spacing:.18em;text-transform:uppercase;font-size:.8rem;color:var(--ink-2)}
.hero h1 span{color:var(--red)}
.lead{font-size:1.15rem;max-width:44ch}
.hero-grid{display:grid;grid-template-columns:repeat(9,1fr);aspect-ratio:1;max-width:360px;width:100%;margin:0 auto;border:3px solid var(--ink);background:var(--white)}
.hero-grid i{font-style:normal;display:flex;align-items:center;justify-content:center;font-weight:700;font-size:clamp(.9rem,3.6vw,1.3rem);border-right:1px solid var(--line);border-bottom:1px solid var(--line)}
.hero-grid i:nth-child(3n){border-right:2px solid var(--ink)}
.hero-grid i:nth-child(9n){border-right:0}
.hero-grid i:nth-child(n+19):nth-child(-n+27),.hero-grid i:nth-child(n+46):nth-child(-n+54){border-bottom:2px solid var(--ink)}
.hero-grid i.hot{background:var(--red);animation:pulse 2.4s ease-in-out infinite}
@keyframes pulse{50%{background:var(--paper)}}
@media (prefers-reduced-motion:reduce){.hero-grid i.hot{animation:none}}

/* facts band */
.band{background:var(--ink);color:var(--paper)}
.facts{display:grid;grid-template-columns:repeat(2,1fr);gap:20px;padding-top:28px;padding-bottom:28px}
@media (min-width:860px){.facts{grid-template-columns:repeat(4,1fr)}}
.facts b{display:block;font-weight:900;font-size:2.2rem;line-height:1;color:var(--paper)}
.facts span{font-size:.92rem;opacity:.85}

/* sections */
.section{padding:56px 0}
.section.alt{background:var(--paper-2);border-top:2px solid var(--ink);border-bottom:2px solid var(--ink)}
.split{display:grid;gap:32px;align-items:center}
@media (min-width:860px){.split{grid-template-columns:1fr 1fr}}

/* book cards */
.cards{display:grid;grid-template-columns:repeat(2,1fr);gap:20px;margin-top:24px}
@media (min-width:860px){.cards{grid-template-columns:repeat(4,1fr)}}
.card{text-decoration:none;display:flex;flex-direction:column;gap:4px}
.card img{border:1px solid var(--line);box-shadow:0 1px 0 var(--line);transition:transform .15s}
.card:hover img,.card:focus img{transform:translateY(-4px)}
.card-t{font-weight:900;margin-top:8px;line-height:1.15}
.card-e{font-size:.85rem;color:var(--ink-2)}
.card-s{font-size:.85rem;font-weight:700;color:var(--ink);border-left:6px solid var(--c);padding-left:8px;margin-top:2px}

/* demo steps */
.steps-demo{list-style:none;margin:0;padding:0;display:grid;gap:10px}
.steps-demo li{background:var(--white);border:2px solid var(--ink);padding:12px 14px;border-radius:var(--radius)}
.steps-demo b{display:block;font-size:.8rem;letter-spacing:.12em;text-transform:uppercase;color:var(--red)}

/* series chips */
.chips{list-style:none;padding:0;margin:20px 0 0;display:flex;flex-wrap:wrap;gap:8px}
.chips li{background:var(--c);color:var(--ink);font-weight:700;padding:6px 12px;border-radius:999px}
.chips li.later{background:transparent;border:2px solid var(--c)}

/* book page */
.book{display:grid;gap:32px;padding-top:40px;padding-bottom:56px}
@media (min-width:860px){.book{grid-template-columns:360px 1fr;align-items:start}}
.book-cover img{border:1px solid var(--line)}
.book h1{font-size:clamp(2rem,6vw,3.2rem)}
.book .ed{font-weight:700;color:var(--ink-2);margin-top:-.4em}
.strap{font-weight:900;font-size:1.25rem;border-left:8px solid var(--accent);padding-left:12px}
.ticks{padding:0;list-style:none}
.ticks li{padding:6px 0 6px 30px;position:relative;border-bottom:1px solid var(--line)}
.ticks li::before{content:"";position:absolute;left:4px;top:14px;width:12px;height:12px;background:var(--accent)}
.meta{display:grid;grid-template-columns:auto 1fr;gap:4px 16px;font-size:.95rem;margin:20px 0}
.meta dt{font-weight:700}.meta dd{margin:0}
.buy{margin-top:16px}
.note{font-size:.9rem;color:var(--ink-2)}

/* prose pages */
.prose{max-width:68ch;padding-top:40px;padding-bottom:56px}
.prose h2{margin-top:1.4em}

/* footer */
.foot{background:var(--ink);color:var(--paper);padding:32px 0;margin-top:0}
.foot-in{display:grid;gap:16px}
.foot a{color:var(--paper);text-decoration:none;margin-right:16px;font-weight:600}
.foot a:hover{text-decoration:underline}
.foot-brand{font-weight:900;letter-spacing:.04em}
.foot .small{color:#b9b3a6}

/* ---------- walkthrough player ---------- */
.wt{padding-top:24px;padding-bottom:48px}
.wt-head h1{font-size:clamp(1.5rem,5vw,2.2rem);margin-bottom:.2em}
.wt-head p{color:var(--ink-2);margin-bottom:12px}
.wt-body{display:grid;gap:20px}
@media (min-width:860px){.wt-body{grid-template-columns:minmax(0,520px) 1fr;align-items:start}}
.board{display:grid;grid-template-columns:repeat(9,1fr);aspect-ratio:1;width:100%;max-width:520px;border:3px solid var(--ink);background:var(--white);user-select:none}
.cell{position:relative;border-right:1px solid var(--line);border-bottom:1px solid var(--line);display:flex;align-items:center;justify-content:center;font-weight:700;font-size:clamp(1rem,5.4vw,1.8rem);transition:background .25s}
.cell.c2,.cell.c5{border-right:2px solid var(--ink)}
.cell.c8{border-right:0}
.cell.r2,.cell.r5{border-bottom:2px solid var(--ink)}
.cell.r8{border-bottom:0}
.cell.given{color:var(--ink)}
.cell.solved{color:#2a5bd7}
.cell.unit{background:#fbf3d9}
.cell.pat{background:#f6dd8f}
.cell.focus{background:var(--accent)}
.cell.focus.solved{color:var(--ink)}
.cell.elimc{background:#fde7e7}
.cands{position:absolute;inset:0;display:grid;grid-template-columns:repeat(3,1fr);font-size:clamp(.45rem,2vw,.72rem);font-weight:600;color:#8a857a;padding:1px}
.cands span{display:flex;align-items:center;justify-content:center}
.cands span.gone{color:#d23b3b;text-decoration:line-through;font-weight:900}
.cands span.keep{color:var(--ink);font-weight:900}
.panel{background:var(--white);border:2px solid var(--ink);border-radius:var(--radius);padding:16px}
.panel .count{font-size:.8rem;font-weight:700;letter-spacing:.12em;text-transform:uppercase;color:var(--ink-2)}
.panel h2{font-size:1.4rem;text-transform:none;margin:.2em 0 .4em}
.panel .tier{display:inline-block;font-size:.72rem;font-weight:700;letter-spacing:.1em;text-transform:uppercase;padding:2px 8px;border-radius:999px;background:var(--paper-2);margin-left:6px;vertical-align:middle}
.panel .tier.expert{background:var(--ink);color:var(--paper)}
.panel .what{font-size:1.05rem}
.panel .why{color:var(--ink-2);font-size:.95rem}
.controls{display:flex;flex-wrap:wrap;gap:8px;margin:14px 0 6px}
.controls button{font:inherit;font-weight:700;background:var(--ink);color:var(--paper);border:2px solid var(--ink);border-radius:var(--radius);padding:.55em .95em;cursor:pointer;min-width:44px;min-height:44px}
.controls button.ghost{background:transparent;color:var(--ink)}
.controls button:disabled{opacity:.4;cursor:default}
.progress{height:6px;background:var(--paper-2);border-radius:3px;overflow:hidden;margin-top:6px}
.progress i{display:block;height:100%;background:var(--accent);width:0;transition:width .2s}
.wt-foot{margin-top:16px;font-size:.9rem;color:var(--ink-2)}
.toggle{font-size:.9rem;display:flex;align-items:center;gap:6px;margin-top:6px}
/* killer sudoku walkthroughs: cage overlay drawn by walkthrough.js */
.board{position:relative}
.board .cages{position:absolute;inset:0;width:100%;height:100%;pointer-events:none}
.cage-line{fill:none;stroke:#444;stroke-width:.03;stroke-dasharray:.09 .06}
.cage-sum{font-size:.24px;font-weight:700;fill:var(--ink);paint-order:stroke;stroke:var(--white);stroke-width:.06px}