/* Mobile first: base rules are the phone layout. @media (min-width: 900px) adds the desktop sidebar. */
:root{--ink:#0a0a0a;--body:#242424;--meta:#5c5c5c;--rule:#e2e2e2;--soft:#f6f6f4;--side:#fafaf8;--accent:#d71921;--ok:#1a7f37;--med:#9a6700;--bar:57px;
--sans:-apple-system,BlinkMacSystemFont,"Inter","Helvetica Neue",Arial,sans-serif;--mono:ui-monospace,"SF Mono",Menlo,Consolas,monospace}
*{box-sizing:border-box}html{scroll-behavior:smooth;-webkit-text-size-adjust:100%;text-size-adjust:100%}
body{margin:0;font:16px/1.65 var(--sans);color:var(--body);background:#fff;-webkit-tap-highlight-color:transparent}
a{color:var(--ink)}
:focus-visible{outline:2px solid var(--accent);outline-offset:2px}
button,select,input{font:inherit}
button,select,summary,label,.done{touch-action:manipulation}

/* top bar (phone + tablet) */
.topbar{display:flex;align-items:center;gap:10px;position:sticky;top:0;z-index:30;min-height:var(--bar);background:rgba(255,255,255,.96);-webkit-backdrop-filter:blur(6px);backdrop-filter:blur(6px);border-bottom:1px solid var(--rule);padding:8px max(14px,env(safe-area-inset-right)) 8px max(14px,env(safe-area-inset-left));padding-top:max(8px,env(safe-area-inset-top))}
.topbar button{font:600 15px var(--sans);border:1px solid var(--rule);background:#fff;border-radius:8px;min-height:44px;padding:0 16px;color:var(--ink)}
.topbar .tt{flex:1;min-width:0;font-weight:700;color:var(--ink);white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.topbar .tp{font:12px var(--mono);color:var(--meta)}

/* contents: an off-canvas drawer on small screens */
aside{position:fixed;z-index:40;top:0;left:0;bottom:0;width:min(86vw,320px);overflow:auto;-webkit-overflow-scrolling:touch;overscroll-behavior:contain;background:var(--side);border-right:1px solid var(--rule);
  padding:max(16px,env(safe-area-inset-top)) 0 max(40px,env(safe-area-inset-bottom)) env(safe-area-inset-left);
  transform:translateX(-100%);visibility:hidden;transition:transform .25s ease,visibility 0s .25s}
body.nav-open aside{transform:none;visibility:visible;transition:transform .25s ease;box-shadow:0 0 40px rgba(0,0,0,.18)}
.scrim{position:fixed;inset:0;z-index:35;background:rgba(0,0,0,.45);opacity:0;pointer-events:none;transition:opacity .25s}
body.nav-open .scrim{opacity:1;pointer-events:auto}
aside .close{position:absolute;top:max(10px,env(safe-area-inset-top));right:10px;border:1px solid var(--rule);background:#fff;border-radius:8px;width:44px;height:44px;font-size:18px;color:var(--ink)}
aside .brand{padding:0 64px 4px 20px;font-weight:700;color:var(--ink)}
aside .prog{padding:0 64px 12px 20px;font:12px var(--mono);color:var(--meta)}
aside .bar{height:3px;background:var(--rule);margin:0 20px 14px}aside .bar i{display:block;height:100%;background:var(--ink);width:0}
aside input.q{margin:0 20px 6px;width:calc(100% - 40px);min-height:44px;padding:8px 12px;border:1px solid var(--rule);border-radius:8px;font-size:16px}
.part{margin:18px 20px 0;padding-top:12px;border-top:1px solid var(--rule);font-weight:700;color:var(--ink);font-size:13px}
.grp{padding:12px 20px 2px;font:12px var(--mono);text-transform:uppercase;letter-spacing:.07em;color:var(--meta)}
aside a{display:flex;align-items:center;gap:12px;min-height:44px;padding:8px 20px;color:var(--body);text-decoration:none;font-size:15px;border-left:2px solid transparent}
aside a.on{border-left-color:var(--ink);background:#efefea;color:var(--ink);font-weight:600}
aside a span{flex:1}aside a em{font:11px var(--mono);font-style:normal}
aside a.isdone span{color:var(--meta);text-decoration:line-through}
.done{accent-color:var(--ink);margin:0;width:20px;height:20px;flex:none}
.d-Easy{color:var(--ok)}.d-Medium{color:var(--med)}

/* content */
main{min-width:0;max-width:820px;padding:20px max(16px,env(safe-area-inset-right)) 96px max(16px,env(safe-area-inset-left))}
article,section,.partHead,.intro{scroll-margin-top:calc(var(--bar) + 8px)}
.intro h1{font-size:26px;line-height:1.2;color:var(--ink);margin:0 0 8px}
.lead{color:var(--meta)}
.partHead{margin-top:56px;padding:20px 0 0;border-top:3px solid var(--ink)}
.partHead h1{font-size:24px;color:var(--ink);margin:0}
section.ch{border-top:1px solid var(--rule);margin-top:40px;padding-top:24px}
section.ch>h2{font-size:21px;color:var(--ink);margin:0 0 4px}
section.ch>p{color:var(--meta);margin:0 0 8px}
.page{padding:24px 0 8px;border-bottom:1px dashed var(--rule)}
.page h1.title,.page h2{font-size:19px;color:var(--ink);margin:4px 0 8px}
.crumb{font:12px var(--mono);color:var(--meta)}.crumb a{color:var(--meta);display:inline-block;padding:6px 0}
.page h2.sub{font-size:13px;text-transform:uppercase;letter-spacing:.05em;color:var(--meta);margin:18px 0 4px}
ul{margin:0 0 10px;padding-left:20px}li{margin:4px 0}
pre{font:12.5px/1.55 var(--mono);background:var(--soft);border:1px solid var(--rule);border-radius:6px;padding:12px;overflow-x:auto;-webkit-overflow-scrolling:touch;margin:10px 0}
pre.code{position:relative;background:#fbfbfa;padding-top:44px}
.copy{position:absolute;top:6px;right:6px;font:12px var(--mono);border:1px solid var(--rule);background:#fff;border-radius:6px;min-height:32px;padding:4px 12px;cursor:pointer}
.k{color:#8250df}.s{color:#0a3069}.c{color:#6e7781;font-style:italic}.n{color:#0550ae}
details{border:1px solid var(--rule);border-radius:8px;margin:8px 0;padding:0 14px}
details summary{cursor:pointer;min-height:44px;padding:11px 0;font-weight:600;color:var(--ink)}
details[open]{padding-bottom:6px}details.hint summary{color:var(--med)}
.cx{font:13px var(--mono);color:var(--meta)}
.what{font-size:17px;color:var(--ink)}
.real{background:var(--soft);border-radius:6px;padding:10px 14px;margin:14px 0 4px}
.say{border-left:2px solid var(--ink);padding:4px 0 4px 14px;margin:16px 0 4px;color:var(--ink)}
table{display:block;overflow-x:auto;-webkit-overflow-scrolling:touch;border-collapse:collapse;width:100%;font-size:14px;margin:10px 0}
td,th{border-top:1px solid var(--rule);padding:8px 12px 8px 0;text-align:left;vertical-align:top}
th{font:11px var(--mono);text-transform:uppercase;color:var(--meta);font-weight:400}
.cols{display:grid;grid-template-columns:minmax(0,1fr);gap:0 28px}
footer{margin-top:64px;font:12px var(--mono);color:var(--meta)}

/* animation player */
.anim{border:1px solid var(--rule);border-radius:8px;padding:12px 10px 10px;margin:12px -6px;background:#fff;--cur:#fde68a;--cmp:#dbeafe;--ok:#bbf7d0;--bad:#fecaca;--dim:#f1f1ef}
.anim:focus-visible{outline:2px solid var(--accent)}
details.watch{border-color:var(--ink)}details.watch .anim{border:0;padding:4px 0 8px;margin:0}
.stage{display:flex;flex-direction:column;gap:12px;min-height:60px}
.view{overflow-x:auto;-webkit-overflow-scrolling:touch}
.view .vl{font:11px var(--mono);text-transform:uppercase;letter-spacing:.05em;color:var(--meta);margin-bottom:4px}
.row{display:flex;flex-wrap:wrap;gap:4px}
.slot{display:flex;flex-direction:column;align-items:center;min-width:32px}
.cell{min-width:32px;height:32px;padding:0 5px;display:flex;align-items:center;justify-content:center;border:1px solid #cfcfca;border-radius:5px;font:12px var(--mono);color:var(--ink);background:#fff;transition:background .25s,border-color .25s,opacity .25s}
.cell.cur{background:var(--cur);border-color:#d97706}.cell.cmp{background:var(--cmp);border-color:#3b82f6}.cell.ok{background:var(--ok);border-color:#16a34a}.cell.bad{background:var(--bad);border-color:#dc2626}.cell.dim{background:var(--dim);color:#aaa;border-color:#e5e5e0}
.cell.node{border-radius:17px}
.ix{font:10px var(--mono);color:var(--meta);height:14px}.ptr{font:11px var(--mono);color:var(--accent);font-weight:700;height:14px;white-space:nowrap}
.empty{font:12px var(--mono);color:var(--meta);padding:8px 0}.nil{font:11px var(--mono);color:#bbb}
.kv{display:flex;flex-wrap:wrap;gap:6px}.pair{display:flex;border:1px solid #cfcfca;border-radius:5px;font:13px var(--mono);overflow:hidden;transition:background .25s}
.pair b{padding:5px 8px;background:var(--soft);font-weight:600}.pair span{padding:5px 8px}.pair.cur{border-color:#d97706}.pair.cur span,.pair.cur b{background:var(--cur)}
.vars{display:flex;flex-wrap:wrap;gap:6px 16px;font:13px var(--mono)}.vars i{font-style:normal;color:var(--meta)}
.grid{display:grid;gap:3px}.grid .cell{min-width:30px;width:30px;height:30px}
.buckets{display:flex;flex-direction:column;gap:4px}.bk{display:flex;align-items:center;gap:4px;padding:3px 6px;border-radius:5px;min-height:38px;transition:background .25s}.bk.on{background:#fafaf2}.bk .ix{width:18px;height:auto}.chip{min-width:0;height:28px}
.svg{width:100%;min-width:440px;max-width:560px;height:auto;display:block}
.svg line{stroke:#bdbdb7;stroke-width:1.5;transition:stroke .25s}.svg line.cur{stroke:#d97706;stroke-width:2.5}.svg line.cmp{stroke:#3b82f6}
.svg marker path{fill:#9a9a94}
.svg text{font:12px var(--mono);text-anchor:middle;fill:var(--ink)}.svg text.sub{font-size:11px;fill:var(--accent);font-weight:700}.svg text.w{fill:var(--meta)}
.svg text.sub,.svg text.w{paint-order:stroke;stroke:#fff;stroke-width:4px;stroke-linejoin:round}.svg text.tick{font-size:10px;fill:var(--meta)}.svg text.bl{text-anchor:start;font-size:11px}
.nd circle,.nd rect{fill:#fff;stroke:#9a9a94;stroke-width:1.5;transition:fill .25s,stroke .25s}
.nd.cur circle,.nd.cur rect{fill:var(--cur);stroke:#d97706}.nd.cmp circle,.nd.cmp rect{fill:var(--cmp);stroke:#3b82f6}.nd.ok circle,.nd.ok rect{fill:var(--ok);stroke:#16a34a}.nd.bad circle,.nd.bad rect{fill:var(--bad);stroke:#dc2626}
.note{min-height:3.2em;margin:10px 0 6px;color:var(--ink);font-size:15px}
.ctl{display:flex;align-items:center;gap:6px;flex-wrap:wrap}
.ctl button,.ctl select{font:14px var(--mono);border:1px solid var(--rule);background:#fff;border-radius:8px;min-height:44px;min-width:44px;padding:4px 10px;cursor:pointer;color:var(--ink)}
.ctl .play{min-width:72px;background:var(--ink);color:#fff;border-color:var(--ink)}
.ctl input{order:9;flex:1 1 100%;height:44px;margin:0;accent-color:var(--ink)}
.ctl input::-webkit-slider-thumb{width:26px;height:26px}.ctl input::-moz-range-thumb{width:26px;height:26px}
.ctl .cnt{font:12px var(--mono);color:var(--meta);margin-left:auto;text-align:right}

@media (max-width:899.98px){body.nav-open{overflow:hidden}} /* scroll lock only while the drawer exists */

/* tablet: roomier content, two-column cheat sheet */
@media (min-width:600px){
  main{padding:28px 32px 120px}
  .intro h1{font-size:30px}
  .cols{grid-template-columns:minmax(0,1fr) minmax(0,1fr)}
  .anim{padding:14px 16px 10px;margin:14px 0}
  table{display:table}
}

/* desktop: permanent sidebar, no top bar, mouse-sized controls */
@media (min-width:900px){
  body{display:grid;grid-template-columns:300px minmax(0,1fr);min-height:100vh}
  .topbar,.scrim,aside .close{display:none}
  aside{grid-column:1;grid-row:1;position:sticky;top:0;height:100vh;width:auto;z-index:auto;transform:none;visibility:visible;transition:none;box-shadow:none;padding:20px 0 40px}
  aside .brand,aside .prog{padding-right:20px}
  aside a{min-height:0;padding:4px 20px;font-size:14.5px;gap:8px}aside a:hover{background:#f0f0ec}
  aside input.q{min-height:0;padding:7px 10px;font-size:14px}
  .grp{padding:10px 20px 2px;font-size:11px}
  .done{width:auto;height:auto}
  main{grid-column:2;grid-row:1;padding:40px 56px 120px}
  article,section,.partHead,.intro{scroll-margin-top:16px}
  .intro h1{font-size:32px}.partHead{margin-top:72px}.partHead h1{font-size:28px}
  section.ch{margin-top:48px;padding-top:28px}section.ch>h2{font-size:24px}
  .page{padding-top:28px}.page h1.title,.page h2{font-size:21px}
  pre{font-size:13.5px;padding:12px 14px}pre.code{padding-top:34px}
  .copy{top:8px;right:8px;font-size:11px;min-height:0;padding:2px 8px;border-radius:4px}
  details summary{min-height:0;padding:9px 0}
  table{font-size:14.5px}td,th{padding:7px 10px 7px 0}
  .slot{min-width:38px}.cell{min-width:38px;height:34px;padding:0 6px;font-size:13px}.grid .cell{min-width:34px;width:34px;height:34px}
  .svg{min-width:0}
  .ctl button,.ctl select{font-size:12px;min-height:0;min-width:0;padding:4px 9px;border-radius:5px}
  .ctl .play{min-width:58px}
  .ctl input{order:0;flex:1 1 120px;height:auto}
  .ctl input::-webkit-slider-thumb{width:auto;height:auto}.ctl input::-moz-range-thumb{width:auto;height:auto}
  .ctl .cnt{font-size:11px;margin-left:0;min-width:52px}
}
@media (hover:hover){aside a:hover{background:#f0f0ec}}
/* touch screens at desktop width (tablet landscape): keep finger-sized targets */
@media (min-width:900px) and (pointer:coarse){
  aside a{min-height:44px;padding:8px 20px}details summary{min-height:44px;padding:11px 0}
  .ctl button,.ctl select{min-height:44px;min-width:44px;font-size:14px;padding:4px 10px}
  .ctl input{order:9;flex:1 1 100%;height:44px}.ctl .cnt{margin-left:auto}
}
@media (prefers-reduced-motion:reduce){html{scroll-behavior:auto}aside,.scrim,.cell,.pair,.bk,.svg line,.nd circle,.nd rect{transition:none}}
@media print{.topbar,.scrim,aside,.anim,.copy{display:none}body{display:block}main{padding:0}details{border:0;padding:0}details>*{display:block}}

/* multi-page book */
.page{border-bottom:0;padding-top:4px}
.crumb a{text-decoration:none}
.donebox{display:flex;align-items:center;gap:12px;margin:32px 0 0;padding:14px 16px;border:1px solid var(--rule);border-radius:8px;font-weight:600;color:var(--ink);min-height:52px;cursor:pointer}
.donebox input{width:22px;height:22px;accent-color:var(--ink);margin:0}
.pager{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1fr);gap:10px;margin:16px 0 0}
.pager a{display:flex;flex-direction:column;gap:2px;min-height:64px;padding:10px 14px;border:1px solid var(--rule);border-radius:8px;text-decoration:none;color:var(--ink);overflow:hidden}
.pager a small{font:11px var(--mono);text-transform:uppercase;letter-spacing:.05em;color:var(--meta)}
.pager a span{font-weight:600;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.pager .nx{text-align:right;grid-column:2}
.ask{background:var(--soft);border-radius:8px;padding:10px 14px 4px;margin:12px 0}
.ask h2.sub{margin-top:4px}
pre.plain{white-space:pre-wrap;word-break:break-word}
@media (hover:hover){.pager a:hover,.donebox:hover{border-color:var(--ink)}}