:root{--bg:#fbfaf8;--surface:#fff;--ink:#1d1d22;--muted:#6b6b75;--line:#e2e0e6;--soft:#f3f1f6;--acc:#7c4dff;--acc-soft:#efe9ff;--good:#1f8a5b;--good-soft:#e5f5ec;--bad:#c0392b;--bad-soft:#fdecea;--warn:#b7791f;--warn-soft:#fdf3e2;--info:#2f6fdb;--info-soft:#e8f0fd;--think:#8a5a00;--radius:12px;color-scheme:light}@media (prefers-color-scheme:dark){:root{--bg:#141418;--surface:#1c1c22;--ink:#ececf1;--muted:#a0a0ab;--line:#33333d;--soft:#24242c;--acc:#a78bfa;--acc-soft:#2a2340;--good:#4ade80;--good-soft:#15281e;--bad:#f87171;--bad-soft:#321a1a;--warn:#f0b552;--warn-soft:#2d2415;--info:#7aa7f7;--info-soft:#18233a;--think:#f0c46a;color-scheme:dark}}*{box-sizing:border-box}html{background:var(--bg);color:var(--ink)}body{margin:0;font:17px/1.6 Iowan Old Style,Charter,"Noto Serif",Georgia,serif;-webkit-font-smoothing:antialiased}.badge,.box-h,.btn,.chip,.crumbs,.lesson-card,.lvl,.opt,.stat b,.sym,.symbols,.testat-bar,.top,h1,h2,h3,th{font-family:system-ui,-apple-system,Segoe UI,Noto Sans,sans-serif}h1{font-size:2rem;line-height:1.2;margin:.3em 0 .2em}h2{font-size:1.4rem;margin:2.2em 0 .6em;padding-top:.4em;border-top:1px solid var(--line)}h3{font-size:1.1rem;margin:1.6em 0 .5em}a{color:var(--acc)}.mono,code{font-family:ui-monospace,JetBrains Mono,SF Mono,Menlo,monospace;font-size:.92em}.muted{color:var(--muted)}.small{font-size:.85rem}.nowrap{white-space:nowrap}.lead{font-size:1.1rem;color:var(--muted)}ul.tight{margin:.3em 0;padding-left:1.3em}ul.tight li{margin:.15em 0}.top{display:flex;align-items:baseline;gap:1rem;padding:.8rem 1.2rem;border-bottom:1px solid var(--line);background:var(--surface);position:-webkit-sticky;position:sticky;top:0;z-index:5}.brand{font-weight:700;text-decoration:none;color:var(--ink)}.page{padding:1.2rem 1rem 3rem}.foot,.page{max-width:820px;margin:0 auto}.foot{padding:1.5rem 1rem 3rem;border-top:1px solid var(--line)}.crumbs,.crumbs a{color:var(--muted)}.ov{display:inline-block;position:relative;line-height:1.1;padding-top:.08em}.ov:before{content:"";position:absolute;left:.02em;right:.02em;top:0;border-top:.08em solid}.btn{display:inline-flex;align-items:center;gap:.4em;border:1px solid var(--acc);background:var(--acc);color:#fff;padding:.5em 1em;border-radius:999px;font-size:.92rem;font-weight:600;cursor:pointer;text-decoration:none}@media (prefers-color-scheme:dark){.btn{color:#141418}}.btn:hover{filter:brightness(1.08)}.btn:disabled{opacity:.45;cursor:not-allowed}.btn.ghost{background:transparent;color:var(--acc)}.btn.big{font-size:1.05rem;padding:.7em 1.4em}.link{background:none;border:0;color:var(--acc);cursor:pointer;padding:0;font:inherit;text-decoration:underline}.row{display:flex;flex-wrap:wrap;align-items:center;gap:.6rem;margin:.8rem 0 .2rem}.chip{border:1px solid var(--line);background:var(--surface);color:var(--ink);border-radius:999px;padding:.25em .9em;font-size:.9rem;cursor:pointer}.chip.on{background:var(--acc);border-color:var(--acc);color:#fff}.chip.big{font-size:1rem;padding:.45em 1.2em}input.text{font-size:1rem;padding:.55em .8em;border-radius:10px;border:1px solid var(--line);background:var(--surface);color:var(--ink);min-width:0;width:100%}input.text.short{width:7em}input.text:focus{outline:2px solid var(--acc);outline-offset:1px}.box{border:1px solid var(--line);background:var(--surface);border-radius:var(--radius);padding:.9rem 1.1rem;margin:1.1rem 0}.box-h{display:flex;justify-content:space-between;align-items:center;gap:.6rem;font-size:.8rem;font-weight:700;text-transform:uppercase;letter-spacing:.05em;margin-bottom:.4rem}.box-h,.src{color:var(--muted)}.src{font-family:system-ui,sans-serif;font-size:.75rem;font-weight:400;text-transform:none;letter-spacing:0;margin-left:.5em}.def{border-left:4px solid var(--acc)}.def .box-h{color:var(--acc)}.note.idea{background:var(--info-soft);border-color:transparent}.note.idea .box-h{color:var(--info)}.note.tip{background:var(--acc-soft);border-color:transparent}.note.tip .box-h{color:var(--acc)}.note.warn{background:var(--warn-soft);border-color:transparent}.note.warn .box-h{color:var(--warn)}.note.think{background:var(--warn-soft);border-color:transparent}.note.think .box-h{color:var(--think)}.box ol,.box ul{padding-left:1.3em;margin:.3em 0}table.plain{border-collapse:collapse;width:100%;font-size:.95rem}table.plain td,table.plain th{padding:.3em .6em;border-bottom:1px solid var(--line);text-align:left;vertical-align:top}.walk{border-left:4px solid var(--good)}.walk .box-h{color:var(--good)}.walk-problem{font-weight:600;margin-bottom:.5rem}.walk-steps{padding-left:1.4em;margin:.3rem 0}.walk-steps li{margin:.7rem 0}.think{color:var(--think);font-style:italic;font-size:.95rem}.say{margin-top:.15rem}.walk-result{background:var(--good-soft);padding:.6rem .8rem;border-radius:8px;margin-top:.5rem}.exercise{border:2px solid var(--acc-soft)}.exercise .box-h{color:var(--acc)}.exercise.solved{border-color:color-mix(in srgb,var(--good) 45%,transparent)}.ex-meta{display:flex;gap:.4rem}.badge,.lvl{font-size:.7rem;padding:.15em .6em;border-radius:999px;text-transform:none;letter-spacing:0}.badge.ok{background:var(--good-soft);color:var(--good)}.badge.tried{background:var(--warn-soft);color:var(--warn)}.lvl{background:var(--soft);color:var(--muted);font-weight:600}.q{margin:.3rem 0 .6rem;font-weight:500}.feedback{border-radius:8px;padding:.55rem .8rem;margin:.7rem 0 .3rem}.feedback.good{background:var(--good-soft)}.feedback.bad{background:var(--bad-soft)}.solution{background:var(--soft);border-radius:8px;padding:.6rem .9rem;margin:.6rem 0}.solution p{margin:.3em 0}.hint{margin-top:.5rem}.hint-body{background:var(--acc-soft);padding:.5rem .8rem;border-radius:8px;margin-top:.3rem}.why{margin:.2rem 0 .4rem 2rem;font-size:.92rem}.why.right{color:var(--good)}.why.wrong{color:var(--bad)}.fade-in{animation:fade .25s ease-out}@keyframes fade{0%{opacity:0;transform:translateY(3px)}to{opacity:1;transform:none}}.options{list-style:none;padding:0}.opt,.options{margin:.3rem 0}.opt{display:flex;gap:.7em;align-items:flex-start;width:100%;text-align:left;border:1px solid var(--line);background:var(--surface);color:var(--ink);border-radius:10px;padding:.55em .8em;cursor:pointer;font-size:.97rem;line-height:1.45}.opt.picked,.opt:hover:not(:disabled){border-color:var(--acc)}.opt.picked{background:var(--acc-soft)}.opt.right{border-color:var(--good);background:var(--good-soft)}.opt.wrong{border-color:var(--bad);background:var(--bad-soft)}.opt-mark{color:var(--acc)}.tf-table{width:100%;border-collapse:collapse}.tf-table td{padding:.5rem .3rem;border-bottom:1px solid var(--line);vertical-align:top}.tf-table tr.right{background:color-mix(in srgb,var(--good-soft) 70%,transparent)}.tf-table tr.wrong{background:color-mix(in srgb,var(--bad-soft) 80%,transparent)}.tf-table .why{margin:.3rem 0 0;color:var(--muted)}.tf-btns{white-space:nowrap;text-align:right;width:1%}.tf-btns .chip{margin-left:.3rem}.symbols{display:flex;gap:.3rem;margin-top:.4rem;flex-wrap:wrap}.sym{min-width:2.2em;border:1px solid var(--line);background:var(--soft);color:var(--ink);border-radius:8px;padding:.2em .5em;cursor:pointer;font-size:1rem}.tt-scroll{overflow-x:auto}table.truth{border-collapse:collapse;margin:.6rem 0;font-size:.95rem}table.truth td,table.truth th{border:1px solid var(--line);padding:0;text-align:center;min-width:2.6em}table.truth th{background:var(--soft);padding:.35em .6em;white-space:nowrap;font-weight:600}table.truth th.final{background:var(--acc-soft);color:var(--acc)}table.truth td.var{background:var(--soft);padding:.3em;font-weight:600}table.truth.static td{padding:.3em .5em}table.truth td.hl{background:var(--bad-soft);font-weight:700}table.truth td.cell button{width:100%;height:2.1em;border:0;background:transparent;color:var(--ink);font-size:1rem;cursor:pointer;font-weight:600}table.truth td.cell button:hover{background:var(--acc-soft)}table.truth td.given{background:var(--soft);color:var(--muted)}table.truth td.right{background:var(--good-soft)}table.truth td.wrong{background:var(--bad-soft)}table.truth td.focus{outline:2px solid var(--bad);outline-offset:-2px}.arrows-wrap{display:grid;grid-template-columns:minmax(220px,320px) 1fr;grid-gap:1rem;gap:1rem;align-items:start}@media (max-width:640px){.arrows-wrap{grid-template-columns:1fr}}.arrow-svg,.graph{width:100%;height:auto;max-width:340px}.hasse-svg{max-width:420px;display:block;margin:0 auto}.blob{fill:none;stroke:var(--line);stroke-width:1.5}.lbl{font:700 14px system-ui,sans-serif;fill:var(--muted)}.arrow{stroke:var(--ink);stroke-width:1.6}.fill-ink{fill:var(--ink)}.fill-acc{fill:var(--acc)}.edge{fill:none;stroke:var(--ink);stroke-width:1.6}.edge.added{stroke:var(--acc);stroke-width:2.2}.hedge{stroke:var(--ink);stroke-width:2}.node circle{fill:var(--surface);stroke:var(--acc);stroke-width:2}.node text{font:700 14px system-ui,sans-serif;fill:var(--ink);pointer-events:none}.arrows .node,.node.clickable{cursor:pointer}.node.sel circle{fill:var(--acc)}.node.sel text{fill:#fff}.node.target circle{stroke-dasharray:3 2}.status{display:grid;grid-gap:.4rem;gap:.4rem}.stat{border-radius:8px;padding:.35rem .6rem;font-size:.95rem}.stat.yes{background:var(--good-soft)}.stat.yes b{color:var(--good)}.stat.no{background:var(--soft)}.stat.no b{color:var(--muted)}.pairs{word-break:break-word;margin:.4rem 0}.figure-row{display:flex;justify-content:center}figure{margin:.8rem 0;text-align:center}figcaption{font-size:.9rem;color:var(--muted);max-width:440px;margin:.3rem auto}.proof-cols{display:grid;grid-template-columns:1fr 1fr;grid-gap:1rem;gap:1rem}@media (max-width:640px){.proof-cols{grid-template-columns:1fr}}.card-step{display:block;width:100%;text-align:left;border:1px dashed var(--line);background:var(--surface);color:var(--ink);border-radius:10px;padding:.5em .7em;margin:.35rem 0;cursor:pointer;font:inherit;font-size:.95rem}.card-step:hover:not(:disabled){border-color:var(--acc);border-style:solid}.card-step.in{border-style:solid;background:var(--acc-soft)}.proof-list{padding-left:1.4em;margin:0;min-height:3rem}.qed{text-align:right;font-size:1.3rem}.chain{background:var(--soft);border-radius:8px;padding:.6rem .9rem;margin-bottom:.6rem;font-size:1.05rem}.chain-row{margin:.25rem 0}.chain-eq{color:var(--muted)}.chain-law{color:var(--acc);font-size:.85rem;margin-left:.7em;font-family:system-ui,sans-serif}.law-opts{display:grid;grid-gap:.1rem;gap:.1rem}.progress{display:inline-block;position:relative;height:6px;width:120px;background:var(--soft);border-radius:99px;overflow:hidden;vertical-align:middle}.progress>*{display:block;position:absolute;inset:0 auto 0 0;background:var(--good);border-radius:99px;transition:width .3s}.progress.big{width:100%;max-width:360px;height:10px}.overall{margin:1rem 0 1.2rem;flex-wrap:wrap}.lesson-meta,.overall{display:flex;align-items:center;gap:.8rem}.lesson-meta{margin-bottom:1rem}.hero{margin:1rem 0 2rem}.lesson-list{list-style:none;padding:0;display:grid;grid-gap:.6rem;gap:.6rem}.lesson-card{display:grid;grid-template-columns:2.4rem 1fr auto;grid-gap:.9rem;gap:.9rem;align-items:center;padding:.8rem 1rem;border:1px solid var(--line);border-radius:var(--radius);background:var(--surface);text-decoration:none;color:var(--ink)}.lesson-card:hover{border-color:var(--acc)}.lesson-card .num{display:grid;place-items:center;width:2.2rem;height:2.2rem;border-radius:50%;background:var(--acc-soft);color:var(--acc);font-weight:700}.lesson-list li.done .num{background:var(--good-soft);color:var(--good)}.lesson-card .body{display:grid;grid-gap:.2rem;gap:.2rem}.lesson-card .progress{width:100%;max-width:260px;height:4px}@media (max-width:560px){.lesson-card{grid-template-columns:2.4rem 1fr}.lesson-card>.nowrap{grid-column:2}}.pager{gap:1rem;margin-top:3rem;flex-wrap:wrap}.pager,.testat-bar{display:flex;justify-content:space-between}.testat-bar{font-size:.9rem;color:var(--muted)}.testat .progress{width:100%;margin:.4rem 0 1rem}.testat-end,.testat-start{text-align:center;padding:1rem 0}.manim{margin:1.4rem 0}.manim-stage{position:relative;aspect-ratio:16/9;background:#1d1b26;border-radius:var(--radius);overflow:hidden}.manim-canvas,.manim-canvas canvas{width:100%;height:100%;display:block}.manim-overlay,.manim-play{position:absolute;inset:0;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:.6rem;color:#ececf1;font-family:system-ui,sans-serif;text-align:center;padding:1rem}.manim-play{border:0;background:radial-gradient(circle at 50% 45%,#2c2840 0,#1d1b26 70%);cursor:pointer;font-size:1rem;font-weight:600}.manim-play:hover .manim-play-icon{transform:scale(1.08)}.manim-play-icon{display:grid;place-items:center;width:3.4rem;height:3.4rem;border-radius:50%;background:var(--acc);color:#fff;font-size:1.3rem;padding-left:.2rem;transition:transform .15s}.manim-caption{display:flex;justify-content:space-between;align-items:flex-start;gap:1rem;text-align:left;max-width:none;margin:.5rem 0 0;color:var(--ink);font-size:.98rem;min-height:3em}.small-btn{font-size:.8rem;padding:.3em .8em;flex-shrink:0}.manim-script{margin-top:.3rem;color:var(--muted)}.manim-script ol{margin:.3rem 0;padding-left:1.4em}