:root {
  --page: #FFFFFF;
  --ink: #16181D;
  --accent: #1B3A5C;
  --accent-soft: #E9EEF4;
  --signal: #B5452B;
  --rule: #D4D8DE;
  --muted: #535B66;
  --code-bg: #F4F5F7;
  --note-bg: #F7F4EC;
  --serif: "IBM Plex Serif", "Charter", Georgia, serif;
  --sans: "IBM Plex Sans", "Helvetica Neue", Arial, sans-serif;
  --mono: "IBM Plex Mono", Menlo, Consolas, monospace;
}

* { box-sizing: border-box; }
html { background: var(--page); }
body {
  margin: 0;
  color: var(--ink);
  background: var(--page);
  font: 17px/1.68 var(--serif);
  -webkit-text-size-adjust: 100%;
}

.skip { position: absolute; left: -999px; }
.skip:focus { left: 1rem; top: .5rem; background: var(--page); padding: .4rem .8rem; z-index: 10; }

.topbar {
  display: flex; justify-content: space-between; gap: 1rem; flex-wrap: wrap;
  font-family: var(--sans); font-size: .9rem;
  padding: .7rem 1.25rem; border-bottom: 1px solid var(--rule);
}
.topbar a { color: var(--accent); text-decoration: none; font-weight: 600; }
.topbar a.gh { font-weight: 400; color: var(--muted); }

main { max-width: 42rem; margin: 0 auto; padding: 2.25rem 1rem 4rem; }

header { border-bottom: 2px solid var(--accent); padding-bottom: 1.1rem; margin-bottom: 2rem; }
.kicker { font-family: var(--sans); font-size: .9rem; color: var(--muted); margin: 0 0 .6rem; }
.kicker a { color: var(--muted); }
h1, h2, h3, h4 { font-family: var(--sans); color: var(--accent); line-height: 1.25; }
h1 { font-size: 2rem; font-weight: 600; margin: 0; letter-spacing: -.01em; }
.byline { font-family: var(--sans); font-size: .92rem; color: var(--muted); margin: .55rem 0 0; }
h2 { font-size: 1.4rem; font-weight: 600; margin: 2.6rem 0 .8rem; }
h3 { font-size: 1.12rem; font-weight: 600; margin: 2rem 0 .6rem; }
h4 { font-size: 1rem; font-weight: 600; margin: 1.5rem 0 .5rem; }

p { margin: 0 0 1.05rem; }
a { color: var(--accent); text-decoration: underline; text-underline-offset: 3px; text-decoration-thickness: 1px; }
a:hover { color: var(--signal); }
a:focus-visible, summary:focus-visible, button:focus-visible, input:focus-visible {
  outline: 3px solid #E0A526; outline-offset: 2px;
}
a.cite { text-decoration: none; border-bottom: 1px dotted var(--accent); }

ol, ul { padding-left: 1.4rem; margin: 0 0 1.1rem; }
li { margin-bottom: .45rem; }

.code, pre {
  background: var(--code-bg);
  border: 1px solid var(--rule);
  font: 14px/1.55 var(--mono);
  padding: .9rem 1rem;
  margin: 1.1rem 0;
  overflow-x: auto;
  tab-size: 4;
}
.code pre { background: none; border: 0; padding: 0; margin: 0; }
.code .c, .code .c1, .code .cm { color: #5F6B78; font-style: italic; }
.code .s, .code .s1, .code .s2, .code .sa, .code .sd { color: #8A4B14; }
.code .k, .code .kn, .code .ow { color: var(--accent); font-weight: 600; }
.code .mi, .code .mf { color: #6B3FA0; }
code { font-family: var(--mono); font-size: .9em; }
p code, li code, td code { background: var(--code-bg); padding: .05em .3em; border-radius: 3px; }

table { border-collapse: collapse; margin: 1rem 0 1.5rem; font-size: .94rem; display: block; overflow-x: auto; max-width: 100%; }
th, td { padding: .35rem .8rem .35rem 0; text-align: left; border-bottom: 1px solid var(--rule); vertical-align: top; }
th { font-family: var(--sans); font-weight: 600; border-bottom: 2px solid var(--accent); }
td[align="right"], th[align="right"] { text-align: right; font-variant-numeric: tabular-nums; }

figure { margin: 2rem 0; }
figure img { display: block; width: 100%; height: auto; }
figcaption { font-family: var(--sans); font-size: .9rem; line-height: 1.5; color: var(--muted); margin-top: .6rem; }
figcaption p { margin: 0; }
.fignum { font-weight: 600; color: var(--ink); }

.arithmatex { overflow-x: auto; overflow-y: hidden; }
div.arithmatex { margin: 1rem 0; }
mjx-container { max-width: 100%; }
mjx-container[display="true"] { overflow-x: auto; overflow-y: hidden; }

aside.note {
  background: var(--note-bg); border-left: 3px solid #C9A64B;
  padding: .9rem 1.1rem .2rem; margin: 1.6rem 0;
}
.note-title { font-family: var(--sans); font-weight: 600; margin-bottom: .4rem; }

details.answer { border: 1px solid var(--rule); padding: .55rem .9rem; margin: .6rem 0 1.4rem; }
details.answer summary { font-family: var(--sans); font-size: .92rem; cursor: pointer; color: var(--accent); }
details.answer[open] summary { margin-bottom: .6rem; }

.labcard { border: 1px solid var(--accent); border-radius: 6px; padding: .9rem 1.1rem; margin: 1.6rem 0; background: var(--accent-soft); }
.labcard p { margin: 0; font-family: var(--sans); }
.labcard-kind { font-size: .78rem; text-transform: uppercase; letter-spacing: .08em; color: var(--muted); }
.labcard-title { font-size: 1.05rem; font-weight: 600; margin: .15rem 0 .45rem !important; }
.labcard-title a { text-decoration: none; }
.labcard-links { font-size: .9rem; display: flex; flex-wrap: wrap; gap: .4rem 1.2rem; }
.labcard-links span { color: var(--muted); }

pre.nbcode { background: var(--code-bg); }
pre.nbout { background: var(--page); border-style: dashed; color: #2B3138; }
img.nbimg { display: block; max-width: 100%; height: auto; margin: 1rem 0; }
.nbtable { overflow-x: auto; font-size: .85rem; }

ol.units, ol.lessons { padding-left: 1.6rem; }
ol.units li { margin-bottom: 1rem; }
ol.units a.unit { font-family: var(--sans); font-weight: 600; text-decoration: none; font-size: 1.05rem; }
ol.units span { display: block; font-size: .95rem; color: var(--muted); }
h3.part { font-size: .85rem; text-transform: uppercase; letter-spacing: .08em; color: var(--muted); margin: 2rem 0 .7rem; }
ul.front, ul.practice { list-style: none; padding-left: 0; font-family: var(--sans); }

ol.refs { padding-left: 1.4rem; font-size: .93rem; line-height: 1.55; }
ol.refs li { margin-bottom: .55rem; overflow-wrap: anywhere; }
section.references { margin-top: 3rem; border-top: 1px solid var(--rule); }

.signature { font-family: var(--sans); font-style: italic; color: var(--muted); }

#quiz .q { border-top: 1px solid var(--rule); padding: 1.1rem 0 .4rem; }
#quiz .q-stem p:last-child { margin-bottom: .6rem; }
#quiz label { display: block; padding: .4rem .6rem; margin: .25rem 0; border: 1px solid var(--rule); border-radius: 4px; cursor: pointer; font-size: .97rem; }
#quiz label:hover { border-color: var(--accent); }
#quiz input { margin-right: .55rem; }
#quiz .right { border-color: #2E7D4F; background: #EEF7F1; }
#quiz .wrong { border-color: var(--signal); background: #FBEFEB; }
#quiz .explain { font-size: .94rem; background: var(--note-bg); padding: .6rem .9rem .1rem; margin: .5rem 0 .8rem; }
#quiz .verdict { font-family: var(--sans); font-weight: 600; font-size: .9rem; margin: .4rem 0; }
#quiz button { font: 600 .95rem var(--sans); background: var(--accent); color: #fff; border: 0; border-radius: 4px; padding: .6rem 1.1rem; margin: 1rem .6rem 0 0; cursor: pointer; }
#quiz button.secondary { background: var(--page); color: var(--accent); border: 1px solid var(--accent); }
#quiz .score { font-family: var(--sans); font-size: 1.05rem; margin-top: 1rem; }
.quiz-intro { font-size: .97rem; }

nav.pager { font-family: var(--sans); font-size: .9rem; margin-top: 3.2rem; border-top: 1px solid var(--rule); padding-top: 1rem; display: flex; flex-direction: column; gap: .4rem; }
footer { font-family: var(--sans); font-size: .82rem; color: var(--muted); margin-top: 2.5rem; }

@media (max-width: 520px) {
  body { font-size: 16px; }
  h1 { font-size: 1.6rem; }
  main { padding-top: 1.6rem; }
  table { font-size: .84rem; }
  th, td { padding-right: .55rem; }
  td code, th code { overflow-wrap: anywhere; }
  pre, .code { font-size: 12.5px; }
}
@media (max-width: 400px) {
  mjx-container[display="true"] { font-size: 88%; }
}
@media (prefers-reduced-motion: reduce) {
  * { animation: none !important; transition: none !important; }
}
@media print {
  .topbar, nav.pager, .skip { display: none; }
  main { max-width: none; }
  details.answer { display: block; }
}