:root{
  --bg:#f6f2ea;
  --bg-soft:#efe9dd;
  --ink:#1e1b18;
  --ink-soft:#5b544c;
  --line:#ded5c5;
  --accent:#8c1c13;
  --accent-soft:#b5342a;
  --paper:#fffdf8;
  --maxw:44rem;
}
@media (prefers-color-scheme: dark){
  :root{
    --bg:#14120f;
    --bg-soft:#1c1916;
    --ink:#ece5d9;
    --ink-soft:#a49b8d;
    --line:#332e28;
    --accent:#e0554a;
    --accent-soft:#f07a6e;
    --paper:#1a1714;
  }
}
*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{
  margin:0;
  background:var(--bg);
  color:var(--ink);
  font:400 1.0625rem/1.7 Georgia,"Times New Roman",serif;
  text-rendering:optimizeLegibility;
}
.progress{
  position:fixed;inset:0 auto auto 0;height:3px;width:0;
  background:var(--accent);z-index:50;transition:width .1s linear;
}
.wrap{max-width:var(--maxw);margin:0 auto;padding:0 1.15rem 4rem}

/* ——— Кнопка «в начало» ——— */
.topbtn{
  position:fixed;right:1.5rem;bottom:1.5rem;z-index:55;
  width:2.9rem;height:2.9rem;border-radius:50%;
  background:var(--paper);border:1px solid var(--line);
  box-shadow:0 2px 10px rgba(0,0,0,.14);
  color:var(--accent);font:400 1.3rem/1 Georgia,"Times New Roman",serif;
  cursor:pointer;display:flex;align-items:center;justify-content:center;
  opacity:0;pointer-events:none;transform:translateY(.5rem);
  transition:opacity .25s ease,transform .25s ease,border-color .2s,box-shadow .2s;
}
.topbtn.on{opacity:1;pointer-events:auto;transform:none}
.topbtn:hover{border-color:var(--accent);box-shadow:0 4px 14px rgba(0,0,0,.2)}
.topbtn:active{transform:translateY(1px)}
.topbtn:focus-visible{outline:2px solid var(--accent);outline-offset:3px}
/* подпись — только там, где есть настоящий курсор: на тач-экране она бы залипала */
@media (hover:hover) and (pointer:fine){
  .topbtn::after{
    content:"В начало";
    position:absolute;right:calc(100% + .55rem);top:50%;transform:translateY(-50%);
    background:var(--ink);color:var(--bg);
    font:500 .78rem/1 system-ui,-apple-system,"Segoe UI",sans-serif;
    padding:.45rem .6rem;border-radius:.35rem;white-space:nowrap;
    opacity:0;pointer-events:none;transition:opacity .18s;
  }
  .topbtn:hover::after,.topbtn:focus-visible::after{opacity:1}
}
@media (max-width:36rem){
  .topbtn{right:1rem;bottom:1rem;width:2.6rem;height:2.6rem;font-size:1.15rem}
}
@media (prefers-reduced-motion:reduce){
  .topbtn{transition:opacity .2s ease}
}

/* ——— Обложка ——— */
.cover{
  background:var(--paper);
  border-bottom:1px solid var(--line);
  padding:3.5rem 1.15rem 2.5rem;
  text-align:center;
}
.cover-inner{max-width:var(--maxw);margin:0 auto}
.rule{width:3rem;height:2px;background:var(--accent);margin:1.5rem auto;border:0}
.author{
  font:600 .8rem/1.4 system-ui,-apple-system,"Segoe UI",sans-serif;
  letter-spacing:.22em;text-transform:uppercase;color:var(--accent);margin:0;
}
h1{
  font-size:clamp(2.75rem,17vw,4.5rem);
  line-height:.95;margin:.6rem 0 .4rem;font-weight:700;letter-spacing:-.02em;
}
.subtitle{
  font-style:italic;color:var(--ink-soft);font-size:1.05rem;margin:0;
}
.cover-year{
  font:600 .78rem/1 system-ui,-apple-system,"Segoe UI",sans-serif;
  letter-spacing:.18em;color:var(--ink-soft);margin:1.25rem 0 0;
}
.annotation{
  color:var(--ink-soft);font-size:1rem;margin:1.5rem auto 0;max-width:32rem;text-align:left;
}
.badges{
  display:flex;flex-wrap:wrap;gap:.5rem;justify-content:center;margin-top:1.75rem;
  font:500 .74rem/1 system-ui,-apple-system,"Segoe UI",sans-serif;
}
.badge{
  border:1px solid var(--line);border-radius:99px;padding:.45rem .8rem;
  color:var(--ink-soft);letter-spacing:.04em;background:var(--bg-soft);
}
.badge strong{color:var(--ink);font-weight:600}

/* ——— Типографика ——— */
h2{
  font-size:1.65rem;line-height:1.2;margin:3rem 0 .25rem;letter-spacing:-.01em;
  scroll-margin-top:1rem;
}
h2 .num{
  display:block;
  font:600 .74rem/1 system-ui,-apple-system,"Segoe UI",sans-serif;
  letter-spacing:.2em;text-transform:uppercase;color:var(--accent);margin-bottom:.6rem;
}
h3{font-size:1.15rem;line-height:1.35;margin:2rem 0 .5rem}
p{margin:0 0 1.05rem}
.lead{font-size:1.12rem;color:var(--ink-soft);margin-bottom:1.5rem}
a{color:var(--accent);text-underline-offset:.2em}
em{color:var(--ink)}
mark{
  background:linear-gradient(transparent 58%,color-mix(in srgb,var(--accent) 24%,transparent) 58%);
  color:inherit;padding:0 .05em;
}
.term{font-weight:700;color:var(--accent-soft);font-style:normal}

/* ——— Врезки ——— */
blockquote{
  margin:1.75rem 0;padding:0 0 0 1.1rem;border-left:3px solid var(--accent);
  font-size:1.18rem;line-height:1.5;font-style:italic;
}
blockquote p{margin:0 0 .5rem}
blockquote cite{
  display:block;font:500 .78rem/1.4 system-ui,-apple-system,"Segoe UI",sans-serif;
  font-style:normal;color:var(--ink-soft);letter-spacing:.02em;
}
.key{
  background:var(--bg-soft);border:1px solid var(--line);border-radius:.7rem;
  padding:1.1rem 1.15rem;margin:1.75rem 0;
}
.key .key-title{
  font:700 .72rem/1 system-ui,-apple-system,"Segoe UI",sans-serif;
  letter-spacing:.18em;text-transform:uppercase;color:var(--accent);
  display:block;margin-bottom:.6rem;
}
.key p:last-child{margin-bottom:0}
.formula{
  font:600 1.1rem/1.6 ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;
  text-align:center;color:var(--ink);background:var(--bg-soft);
  border:1px solid var(--line);border-radius:.7rem;padding:.9rem .6rem;margin:1.5rem 0 0;
  overflow-x:auto;
}
ul{padding-left:1.15rem;margin:0 0 1.05rem}
li{margin-bottom:.5rem}

/* ——— Легенда к формуле ——— */
.legend{
  margin:.55rem 0 1.6rem;padding:.85rem 1.05rem;
  background:transparent;border:1px dashed var(--line);border-radius:.7rem;
  font:400 .92rem/1.6 system-ui,-apple-system,"Segoe UI",sans-serif;color:var(--ink-soft);
}
.legend .legend-title{
  display:block;font-size:.68rem;font-weight:700;letter-spacing:.16em;
  text-transform:uppercase;color:var(--accent);margin-bottom:.5rem;
}
.legend dl{margin:0;display:grid;grid-template-columns:auto 1fr;gap:.3rem .75rem;align-items:baseline}
.legend dt{
  font:700 .95rem/1.5 ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;
  color:var(--ink);white-space:nowrap;
}
.legend dd{margin:0}

/* ——— Числовой пример ——— */
.example{
  border-left:3px solid var(--line);padding:.1rem 0 .1rem 1.1rem;margin:1.5rem 0;
  font-size:.97rem;color:var(--ink-soft);
}
.example .example-title{
  display:block;font:700 .68rem/1 system-ui,-apple-system,"Segoe UI",sans-serif;
  letter-spacing:.16em;text-transform:uppercase;color:var(--ink-soft);margin-bottom:.6rem;
}
.example p:last-child{margin-bottom:0}
.example strong{color:var(--ink)}

/* ——— Пошаговая логика ——— */
.steps{
  margin:1.1rem 0;padding-left:1.4rem;
  font-size:.98rem;
}
.steps li{margin-bottom:.6rem}
.steps li:last-child{margin-bottom:0}

/* ——— Микро-резюме части ——— */
.sum{
  margin:2rem 0 0;padding:.9rem 1.1rem;border-radius:.7rem;
  background:var(--paper);border:1px solid var(--line);
  font-size:.98rem;
}
.sum .sum-title{
  font:700 .68rem/1 system-ui,-apple-system,"Segoe UI",sans-serif;
  letter-spacing:.18em;text-transform:uppercase;color:var(--accent);
  display:block;margin-bottom:.55rem;
}
.sum p{margin:0}

/* ——— Навигация ——— */
.toc-nav{
  background:var(--paper);border:1px solid var(--line);border-radius:.7rem;
  padding:1.1rem 1.15rem;margin:2.5rem 0 0;
}
.toc-nav .key-title{
  font:700 .72rem/1 system-ui,-apple-system,"Segoe UI",sans-serif;
  letter-spacing:.18em;text-transform:uppercase;color:var(--accent);
  display:block;margin-bottom:.75rem;
}
.toc-nav ol{margin:0;padding-left:1.15rem}
.toc-nav li{margin-bottom:.45rem}
.toc-nav a{text-decoration:none;border-bottom:1px solid var(--line);color:var(--ink)}

/* ——— Оглавление книги ——— */
details{
  border-top:1px solid var(--line);padding:.35rem 0;
}
details:last-of-type{border-bottom:1px solid var(--line)}
summary{
  cursor:pointer;list-style:none;padding:.85rem 1.75rem .85rem 0;position:relative;
  font-weight:700;font-size:1.02rem;
}
summary::-webkit-details-marker{display:none}
summary::after{
  content:"+";position:absolute;right:.25rem;top:.7rem;
  color:var(--accent);font-size:1.35rem;font-weight:400;line-height:1;
}
details[open] summary::after{content:"–"}
summary small{
  display:block;font:400 .8rem/1.4 system-ui,-apple-system,"Segoe UI",sans-serif;
  color:var(--ink-soft);margin-top:.15rem;
}
details ol{
  margin:0 0 1rem;padding-left:1.35rem;font-size:.97rem;color:var(--ink-soft);
}
details li{margin-bottom:.35rem}

/* ——— Колофон ——— */
.colophon{
  margin-top:4rem;padding-top:2rem;border-top:2px solid var(--line);
  font:400 .88rem/1.65 system-ui,-apple-system,"Segoe UI",sans-serif;color:var(--ink-soft);
}
.colophon h2{
  font:700 .72rem/1 system-ui,-apple-system,"Segoe UI",sans-serif;
  letter-spacing:.18em;text-transform:uppercase;color:var(--accent);margin:0 0 1.25rem;
}
.colophon dl{margin:0 0 1.5rem;display:grid;grid-template-columns:1fr;gap:.15rem}
.colophon dt{
  font-weight:600;color:var(--ink);font-size:.78rem;letter-spacing:.03em;
  text-transform:uppercase;margin-top:.9rem;
}
.colophon dd{margin:0}
.colophon dt:first-child{margin-top:0}
.note{
  background:var(--bg-soft);border-radius:.7rem;padding:.95rem 1.05rem;margin-top:1.5rem;
  font-size:.85rem;
}
.top{
  display:inline-block;margin-top:1.5rem;font-size:.85rem;text-decoration:none;
  border-bottom:1px solid var(--line);
}
@media (min-width:36rem){
  body{font-size:1.125rem}
  .colophon dl{grid-template-columns:11rem 1fr;gap:.5rem 1.25rem}
  .colophon dt{margin-top:0}
}