/* TDS Field Guide — a senior's notebook.
   Graph paper, ink, one yellow highlighter, a red pen for mistakes, a blue pen for notes. */

:root {
  --paper: #f6f6f1;
  --paper-2: #edece5;
  --sheet: #fbfbf8;
  --grid: rgba(38, 78, 160, 0.075);
  --margin-line: rgba(194, 42, 42, 0.3);
  --ink: #16181d;
  --ink-2: #484c55;
  --ink-3: #767a82;
  --rule: #d6d4ca;
  --rule-strong: #16181d;
  --hl: #ffe24a;
  --hl-ink: #16181d;
  --red: #c22a2a;
  --blue: #2743a6;
  --green: #1d7346;
  --slab-red: #ff7a6b;
  --shadow: 0 1px 0 rgba(22, 24, 29, 0.06), 0 12px 24px -18px rgba(22, 24, 29, 0.35);

  --f-display: "Archivo", "Arial Narrow", system-ui, sans-serif;
  --f-body: "IBM Plex Sans", system-ui, -apple-system, "Segoe UI", sans-serif;
  --f-mono: "IBM Plex Mono", ui-monospace, "Cascadia Mono", Consolas, monospace;
  --f-hand: "Kalam", "Segoe Print", "Bradley Hand", cursive;

  --gutter: 16px;
  --measure: 690px;
  color-scheme: light;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --paper: #131519;
    --paper-2: #1a1d22;
    --sheet: #171a1f;
    --grid: rgba(255, 255, 255, 0.035);
    --margin-line: rgba(255, 122, 107, 0.22);
    --ink: #ecebe4;
    --ink-2: #b4b6bb;
    --ink-3: #868990;
    --rule: #2d3138;
    --rule-strong: #ecebe4;
    --hl: #f3d23a;
    --red: #ff7a6b;
    --blue: #9bb0ff;
    --green: #62cf94;
    --slab-red: #c22a2a;
    --shadow: 0 1px 0 rgba(0, 0, 0, 0.4), 0 12px 24px -18px rgba(0, 0, 0, 0.9);
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --paper: #131519;
  --paper-2: #1a1d22;
  --sheet: #171a1f;
  --grid: rgba(255, 255, 255, 0.035);
  --margin-line: rgba(255, 122, 107, 0.22);
  --ink: #ecebe4;
  --ink-2: #b4b6bb;
  --ink-3: #868990;
  --rule: #2d3138;
  --rule-strong: #ecebe4;
  --hl: #f3d23a;
  --red: #ff7a6b;
  --blue: #9bb0ff;
  --green: #62cf94;
  --slab-red: #c22a2a;
  --shadow: 0 1px 0 rgba(0, 0, 0, 0.4), 0 12px 24px -18px rgba(0, 0, 0, 0.9);
  color-scheme: dark;
}

/* ---------- base ---------- */

*, *::before, *::after { box-sizing: border-box; }

html { scroll-behavior: smooth; scroll-padding-top: 72px; -webkit-text-size-adjust: 100%; }
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } }

body {
  margin: 0;
  background-color: var(--paper);
  background-image:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size: 24px 24px;
  color: var(--ink);
  font: 400 17px/1.65 var(--f-body);
  overflow-x: hidden;
}

a { color: var(--blue); text-decoration-thickness: 1px; text-underline-offset: 3px; }
a:hover { text-decoration-thickness: 2px; }
:focus-visible { outline: 2px solid var(--blue); outline-offset: 3px; border-radius: 2px; }

h1, h2, h3, h4 { font-family: var(--f-display); font-stretch: 78%; line-height: 1.02; margin: 0; letter-spacing: -0.01em; }
h3 { font-size: 1.45rem; font-weight: 750; margin: 2.2rem 0 0.6rem; }
h4 { font-size: 1.1rem; font-weight: 700; margin: 1.6rem 0 0.4rem; font-stretch: 85%; }
p { margin: 0 0 1rem; }
ul, ol { padding-left: 1.3rem; margin: 0 0 1rem; }
li { margin: 0.3rem 0; }
code, .mono { font-family: var(--f-mono); font-size: 0.86em; }
strong { font-weight: 600; }
small { font-size: 0.85rem; }

.skip { position: absolute; left: -999px; top: 8px; background: var(--ink); color: var(--paper); padding: 8px 12px; z-index: 100; }
.skip:focus { left: 8px; }

/* The highlighter. Uneven ends, like a real stroke. */
mark {
  color: var(--hl-ink);
  background: linear-gradient(100deg, transparent 0 0.06em, var(--hl) 0.14em calc(100% - 0.12em), transparent calc(100% - 0.03em));
  background-size: 100% 78%;
  background-position: 0 70%;
  background-repeat: no-repeat;
  padding: 0 0.18em;
  margin: 0 -0.18em;
  -webkit-box-decoration-break: clone;
  box-decoration-break: clone;
  border-radius: 0.2em 0.5em 0.3em 0.6em;
}

.eyebrow {
  font: 500 0.74rem/1.3 var(--f-mono);
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--ink-3);
}

/* ---------- top bar ---------- */

.topbar {
  position: sticky; top: 0; z-index: 40;
  background: color-mix(in srgb, var(--paper) 92%, transparent);
  backdrop-filter: saturate(1.2) blur(6px);
  -webkit-backdrop-filter: saturate(1.2) blur(6px);
  border-bottom: 1.5px solid var(--rule-strong);
}
.topbar__in {
  max-width: 1240px; margin: 0 auto; padding: 10px var(--gutter);
  display: flex; align-items: center; gap: 14px;
}
.brand { display: flex; align-items: center; gap: 10px; color: var(--ink); text-decoration: none; min-width: 0; }
.brand__mark { width: 30px; height: 30px; flex: none; }
.brand__name { font: 800 1.15rem/1 var(--f-display); font-stretch: 75%; letter-spacing: 0.01em; text-transform: uppercase; white-space: nowrap; }
.brand__ed { font: 500 0.7rem/1 var(--f-mono); color: var(--ink-3); border: 1px solid var(--rule); padding: 4px 6px; white-space: nowrap; }
.topbar__sp { flex: 1; }
.iconbtn {
  display: inline-flex; align-items: center; justify-content: center; gap: 6px;
  height: 36px; min-width: 36px; padding: 0 10px;
  background: transparent; color: var(--ink); border: 1.5px solid var(--ink);
  font: 500 0.78rem/1 var(--f-mono); cursor: pointer; text-decoration: none; border-radius: 0;
}
.iconbtn:hover { background: var(--ink); color: var(--paper); }
.iconbtn svg { width: 17px; height: 17px; }
@media (max-width: 560px) {
  .brand__ed, .iconbtn .lbl { display: none; }
}

/* ---------- hero ---------- */

.hero { max-width: 1240px; margin: 0 auto; padding: 56px var(--gutter) 24px; }
.hero__grid { display: grid; grid-template-columns: minmax(0, 1fr); gap: 32px; }
@media (min-width: 1000px) { .hero__grid { grid-template-columns: minmax(0, 1.55fr) minmax(0, 1fr); align-items: end; gap: 56px; } }

.hero h1 {
  font-size: clamp(2.7rem, 8.4vw, 6.1rem);
  font-weight: 850; font-stretch: 72%;
  line-height: 0.9; letter-spacing: -0.02em; word-spacing: 0.06em;
  margin: 14px 0 22px;
}
.hero h1 mark { padding: 0 0.08em; margin: 0 -0.08em; background-size: 100% 42%; background-position: 0 88%; }

/* On dark paper the ink is light, so a half-height stroke would leave dark letters on a dark page.
   In dark mode the highlighter covers the whole line and the text stays dark on yellow. */
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) mark { background-size: 100% 100%; background-position: 0 0; padding: 0 0.08em; margin: 0 -0.08em; }
  :root:not([data-theme="light"]) .hero h1 mark { background-size: 100% 88%; background-position: 0 70%; }
}
:root[data-theme="dark"] mark { background-size: 100% 100%; background-position: 0 0; padding: 0 0.08em; margin: 0 -0.08em; }
:root[data-theme="dark"] .hero h1 mark { background-size: 100% 88%; background-position: 0 70%; }
.lede { font-size: 1.14rem; color: var(--ink-2); max-width: 36em; }

.hero__note { position: relative; padding-left: 0; }

/* hand-written note */
.hand { font-family: var(--f-hand); color: var(--blue); font-size: 1.12rem; line-height: 1.35; }

.facts {
  margin: 0; border-top: 1.5px solid var(--rule-strong);
  display: grid; grid-template-columns: 1fr 1fr;
}
.facts div { padding: 14px 12px 14px 0; border-bottom: 1px solid var(--rule); }
.facts div:nth-child(odd) { border-right: 1px solid var(--rule); }
.facts div:nth-child(even) { padding-left: 14px; }
.facts dt { font: 500 0.7rem/1.2 var(--f-mono); letter-spacing: 0.1em; text-transform: uppercase; color: var(--ink-3); margin-bottom: 6px; }
.facts dd { margin: 0; font: 800 1.55rem/1 var(--f-display); font-stretch: 75%; }
.facts dd span { display: block; font: 400 0.84rem/1.35 var(--f-body); color: var(--ink-2); margin-top: 5px; font-stretch: normal; }

.disclaimer {
  margin-top: 26px; font-size: 0.9rem; color: var(--ink-2);
  display: flex; gap: 10px; align-items: flex-start;
}
.disclaimer svg { flex: none; width: 18px; height: 18px; margin-top: 3px; color: var(--red); }

/* ---------- the one rule: an ink slab across the page ---------- */

.rule-slab { max-width: 1240px; margin: 20px auto 34px; padding: 0 var(--gutter); }
.rule-slab__in {
  background: var(--ink); color: var(--paper);
  padding: 28px clamp(18px, 3.4vw, 40px) 26px;
  box-shadow: var(--shadow);
}
.rule-slab__eyebrow {
  margin: 0; font: 500 0.74rem/1.3 var(--f-mono); letter-spacing: 0.14em; text-transform: uppercase;
  color: color-mix(in srgb, var(--paper) 62%, transparent);
}
.rule-slab__big {
  margin: 10px 0 20px;
  font: 850 clamp(2.1rem, 6.4vw, 4.6rem)/0.98 var(--f-display); font-stretch: 72%;
  letter-spacing: -0.02em; word-spacing: 0.06em;
}
.rule-slab__big mark { background-size: 100% 100%; background-position: 0 0; padding: 0 0.08em; margin: 0 -0.08em; }
.rule-slab__except {
  text-decoration: underline wavy var(--slab-red);
  text-decoration-thickness: 3px; text-underline-offset: 0.16em; text-decoration-skip-ink: none;
}
.rule-slab__list { list-style: none; display: flex; flex-wrap: wrap; gap: 8px; padding: 0; margin: 0 0 18px; }
.rule-slab__list li {
  margin: 0; padding: 7px 10px;
  font: 500 0.8rem/1.35 var(--f-mono);
  border: 1.5px solid color-mix(in srgb, var(--paper) 45%, transparent);
}
.rule-slab__small { margin: 0; max-width: 62em; font-size: 0.95rem; color: color-mix(in srgb, var(--paper) 80%, transparent); }
.rule-slab__small em { color: var(--paper); }

/* ---------- term chart ---------- */

.term { max-width: 1240px; margin: 0 auto; padding: 18px var(--gutter) 8px; }
.term__head { display: flex; flex-wrap: wrap; align-items: baseline; gap: 6px 18px; margin-bottom: 14px; }
.term__head h2 { font-size: 1.6rem; font-weight: 800; }
.term__sheet { background: var(--sheet); border: 1.5px solid var(--rule-strong); box-shadow: var(--shadow); }
.term__scroll { overflow-x: auto; -webkit-overflow-scrolling: touch; }
.gantt { position: relative; min-width: 760px; padding: 14px 18px 18px 18px; }
.gantt__months { position: relative; height: 22px; margin-left: 64px; border-bottom: 1px solid var(--rule); }
.gantt__month { position: absolute; top: 0; font: 500 0.7rem/1 var(--f-mono); color: var(--ink-3); text-transform: uppercase; letter-spacing: 0.1em; padding-left: 5px; border-left: 1px solid var(--rule); height: 22px; }
.gantt__rows { position: relative; margin-left: 64px; }
.gantt__vline { position: absolute; top: 0; bottom: 0; width: 0; border-left: 1px dashed var(--rule); }
.gantt__row { position: relative; height: 26px; }
.gantt__row + .gantt__row { border-top: 1px solid color-mix(in srgb, var(--rule) 45%, transparent); }
.gantt__label {
  position: absolute; right: 100%; margin-right: 12px; top: 50%; transform: translateY(-50%);
  font: 600 0.78rem/1 var(--f-mono); white-space: nowrap; color: var(--ink);
}
.gantt__label a { color: inherit; text-decoration: none; }
.gantt__label a:hover { text-decoration: underline; }
.gantt__bar {
  position: absolute; top: 6px; height: 14px;
  border: 1.5px solid var(--ink); background: var(--paper);
}
.gantt__bar--ga { background: repeating-linear-gradient(135deg, transparent 0 4px, color-mix(in srgb, var(--ink) 22%, transparent) 4px 5px); }
.gantt__bar--p { background: var(--blue); border-color: var(--blue); }
.gantt__bar--hl { box-shadow: 0 0 0 3px var(--hl); }
.gantt__dot { position: absolute; top: 4px; width: 18px; height: 18px; margin-left: -9px; transform: rotate(45deg); background: var(--red); border: 1.5px solid var(--red); }
.gantt__dot--et { background: var(--ink); border-color: var(--ink); transform: none; }
.gantt__dates { position: absolute; top: 50%; transform: translateY(-50%); font: 400 0.7rem/1 var(--f-mono); color: var(--ink-2); white-space: nowrap; padding: 2px 4px; margin-left: 4px; background: var(--sheet); z-index: 1; }
.gantt__crunch {
  position: absolute; top: -4px; bottom: -4px;
  background: color-mix(in srgb, var(--hl) 38%, transparent);
  border-left: 1.5px dashed var(--ink); border-right: 1.5px dashed var(--ink);
}
.term__foot { display: flex; flex-wrap: wrap; gap: 8px 22px; padding: 12px 18px; border-top: 1px solid var(--rule); font-size: 0.86rem; color: var(--ink-2); }
.key { display: inline-flex; align-items: center; gap: 8px; }
.key i { display: inline-block; width: 22px; height: 11px; border: 1.5px solid var(--ink); }
.key i.ga { background: repeating-linear-gradient(135deg, transparent 0 4px, color-mix(in srgb, var(--ink) 22%, transparent) 4px 5px); }
.key i.p { background: var(--blue); border-color: var(--blue); }
.key i.roe { width: 11px; transform: rotate(45deg); background: var(--red); border-color: var(--red); }
.key i.et { width: 11px; background: var(--ink); }
.key i.cr { background: color-mix(in srgb, var(--hl) 60%, transparent); border-style: dashed; }
.term__note { margin: 12px 4px 0; }
.scrollhint { display: none; font: 500 0.72rem/1 var(--f-mono); color: var(--ink-3); padding: 10px 18px 0; }
@media (max-width: 800px) { .scrollhint { display: block; } }

/* ---------- layout: index + chapters ---------- */

.book {
  max-width: 1240px; margin: 0 auto; padding: 40px var(--gutter) 40px;
  display: grid; grid-template-columns: minmax(0, 1fr); gap: 40px;
}
@media (min-width: 1040px) { .book { grid-template-columns: 220px minmax(0, 1fr); gap: 56px; } }

.toc { display: none; }
@media (min-width: 1040px) {
  .toc { display: block; position: sticky; top: 76px; align-self: start; max-height: calc(100vh - 96px); overflow: auto; }
}
.toc ol { list-style: none; padding: 0; margin: 10px 0 0; border-top: 1.5px solid var(--rule-strong); }
.toc li { margin: 0; border-bottom: 1px solid var(--rule); }
.toc a {
  display: grid; grid-template-columns: 28px 1fr; gap: 6px; align-items: start;
  padding: 8px 4px; color: var(--ink-2); text-decoration: none; font-size: 0.9rem; line-height: 1.3;
}
/* The chapter you are reading gets its number circled in blue pen, like marking your place in a notebook.
   Nothing is painted behind the title, so it reads the same on light and dark paper. */
.toc a span {
  display: grid; place-items: center; width: 26px; height: 23px; margin: -3px 0 0 -3px;
  font: 500 0.72rem/1 var(--f-mono); color: var(--ink-3);
  border: 2px solid transparent; border-radius: 55% 45% 50% 50% / 50% 55% 45% 50%;
  transform: rotate(-4deg);
  transition: border-color 0.15s, color 0.15s;
}
.toc a:hover { color: var(--ink); }
.toc a:hover span { color: var(--ink); }
.toc a[aria-current="true"] { color: var(--ink); }
.toc a[aria-current="true"] span { border-color: var(--blue); color: var(--blue); font-weight: 600; }
.toc a[aria-current="true"] b { font-weight: 600; }
.toc b { font-weight: 400; }

.toc-m { border: 1.5px solid var(--rule-strong); background: var(--sheet); }
@media (min-width: 1040px) { .toc-m { display: none; } }
.toc-m summary { list-style: none; cursor: pointer; padding: 12px 14px; font: 600 0.8rem/1 var(--f-mono); text-transform: uppercase; letter-spacing: 0.1em; display: flex; justify-content: space-between; align-items: center; }
.toc-m summary::-webkit-details-marker { display: none; }
.toc-m summary::after { content: "+"; font-size: 1.2rem; }
.toc-m[open] summary::after { content: "\2212"; }
.toc-m ol { list-style: none; margin: 0; padding: 0 14px 10px; columns: 2; column-gap: 18px; }
.toc-m li { break-inside: avoid; margin: 0; }
.toc-m a { display: block; padding: 7px 0; color: var(--ink); text-decoration: none; font-size: 0.92rem; line-height: 1.25; }
.toc-m a span { font: 500 0.72rem/1 var(--f-mono); color: var(--ink-3); margin-right: 6px; }
@media (max-width: 420px) { .toc-m ol { columns: 1; } }

/* ---------- chapters ---------- */

.chapter { position: relative; padding: 8px 0 56px; }
.chapter + .chapter { border-top: 1.5px solid var(--rule-strong); padding-top: 40px; }
.chapter__head { display: grid; grid-template-columns: auto minmax(0, 1fr); gap: 4px 18px; align-items: end; margin-bottom: 22px; }
.chapter__no {
  grid-row: span 2;
  font: 800 clamp(3.2rem, 9vw, 5.2rem)/0.8 var(--f-display); font-stretch: 70%;
  color: var(--blue); letter-spacing: -0.03em;
}
.chapter__head h2 { font-size: clamp(2rem, 5.2vw, 3.1rem); font-weight: 820; font-stretch: 74%; }
.chapter__head .eyebrow { align-self: end; }
.chapter__link { color: var(--ink-3); text-decoration: none; font: 500 0.75rem/1 var(--f-mono); margin-left: 8px; opacity: 0; transition: opacity 0.15s; }
.chapter__head:hover .chapter__link, .chapter__link:focus { opacity: 1; }

.prose { max-width: var(--measure); position: relative; }
.prose::after { content: ""; display: block; clear: both; }
.prose > p:first-of-type { font-size: 1.1rem; }
.prose ul li::marker { color: var(--ink-3); }

/* margin notes: float into the page margin on wide screens */
.note {
  display: block; position: relative;
  font-family: var(--f-hand); color: var(--blue);
  font-size: 1.1rem; line-height: 1.35;
  margin: 0.4rem 0 1.4rem; padding-left: 34px;
}
.note::before {
  content: ""; position: absolute; left: 0; top: 0.2em; width: 24px; height: 18px;
  background: currentColor;
  -webkit-mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 18'%3E%3Cpath d='M1 9c5-1 11-1 20 0M15 3c2 2 4 4 6 6-2 2-4 3-6 6' fill='none' stroke='black' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E") no-repeat center / contain;
          mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 18'%3E%3Cpath d='M1 9c5-1 11-1 20 0M15 3c2 2 4 4 6 6-2 2-4 3-6 6' fill='none' stroke='black' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E") no-repeat center / contain;
}
.note b { font-weight: 700; }
@media (min-width: 1240px) {
  .note {
    float: right; clear: right;
    width: 210px; margin: 0.2rem -240px 1rem 0;
    padding-left: 0; transform: rotate(-1.2deg);
  }
  .note::before { position: static; display: block; width: 26px; height: 16px; margin-bottom: 2px; transform: scaleX(-1); }
}

/* ledger table */
.ledger-wrap { overflow-x: auto; margin: 1.2rem 0 1.6rem; border-top: 1.5px solid var(--rule-strong); border-bottom: 1.5px solid var(--rule-strong); }
.ledger { width: 100%; border-collapse: collapse; font-size: 0.93rem; line-height: 1.45; }
.ledger th {
  text-align: left; font: 600 0.7rem/1.2 var(--f-mono); letter-spacing: 0.1em; text-transform: uppercase;
  color: var(--ink-3); padding: 10px 12px 8px 0; border-bottom: 1px solid var(--rule-strong); vertical-align: bottom;
}
.ledger td { padding: 10px 12px 10px 0; border-bottom: 1px solid var(--rule); vertical-align: top; }
.ledger tr:last-child td { border-bottom: 0; }
.ledger td:first-child { font-weight: 600; }
.ledger .tds { color: var(--ink); }
.ledger .other { color: var(--ink-3); }
.ledger--compare td:first-child { width: 22%; }
.ledger--compare td:nth-child(2) { width: 32%; }
.ledger .mono { white-space: nowrap; }
@media (max-width: 640px) {
  .ledger--compare thead { display: none; }
  .ledger--compare tr { display: block; padding: 12px 0; border-bottom: 1px solid var(--rule); }
  .ledger--compare tr:last-child { border-bottom: 0; }
  .ledger--compare td { display: block; width: auto !important; border: 0; padding: 2px 0; }
  .ledger--compare td:nth-child(2)::before { content: "Most courses: "; font: 500 0.7rem/1 var(--f-mono); text-transform: uppercase; letter-spacing: 0.08em; color: var(--ink-3); }
  .ledger--compare td:nth-child(3)::before { content: "TDS: "; font: 600 0.7rem/1 var(--f-mono); text-transform: uppercase; letter-spacing: 0.08em; color: var(--ink); }
  .ledger--then-now td:nth-child(2)::before { content: "Before: "; }
  .ledger--then-now td:nth-child(3)::before { content: "May 2026: "; }
}

/* stacked list rows for GA weeks, topics */
.rows { list-style: none; padding: 0; margin: 1.2rem 0 1.6rem; border-top: 1.5px solid var(--rule-strong); }
.rows > li { margin: 0; padding: 14px 0; border-bottom: 1px solid var(--rule); display: grid; grid-template-columns: 92px minmax(0, 1fr); gap: 4px 16px; }
.rows__k { font: 800 1.35rem/1.05 var(--f-display); font-stretch: 72%; }
.rows__k small { display: block; font: 500 0.7rem/1.3 var(--f-mono); color: var(--ink-3); margin-top: 4px; letter-spacing: 0.02em; font-stretch: normal; }
.rows__v p { margin: 0 0 4px; }
.rows__v .tools { font: 400 0.78rem/1.5 var(--f-mono); color: var(--ink-3); }
@media (max-width: 520px) { .rows > li { grid-template-columns: 1fr; } }

/* numbered steps */
.steps { list-style: none; counter-reset: s; padding: 0; margin: 1.2rem 0 1.6rem; }
.steps > li { counter-increment: s; position: relative; padding: 0 0 14px 52px; margin: 0; min-height: 40px; }
.steps > li::before {
  content: counter(s); position: absolute; left: 0; top: -2px;
  width: 36px; height: 36px; display: grid; place-items: center;
  font: 800 1.2rem/1 var(--f-display); font-stretch: 80%;
  border: 1.5px solid var(--ink); border-radius: 50% 46% 52% 48%;
}
.steps > li strong { display: block; }

/* red pen: mistakes */
.redpen { list-style: none; padding: 0; margin: 1rem 0 1.6rem; }
.redpen li { position: relative; padding-left: 34px; margin: 0.6rem 0; }
.redpen li::before {
  content: ""; position: absolute; left: 2px; top: 0.3em; width: 18px; height: 18px; background: var(--red);
  -webkit-mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 18 18'%3E%3Cpath d='M3 3.5c4 3.5 8 7.5 12 11.5M15 2.5c-4 4-8 8.5-12 12.5' fill='none' stroke='black' stroke-width='2.4' stroke-linecap='round'/%3E%3C/svg%3E") no-repeat center / contain;
          mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 18 18'%3E%3Cpath d='M3 3.5c4 3.5 8 7.5 12 11.5M15 2.5c-4 4-8 8.5-12 12.5' fill='none' stroke='black' stroke-width='2.4' stroke-linecap='round'/%3E%3C/svg%3E") no-repeat center / contain;
}
.redpen--tick li::before {
  background: var(--green);
  -webkit-mask-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 18 18'%3E%3Cpath d='M2.5 9.5c1.8 1.6 3.4 3.4 5 5.5 2.4-5 5.4-9 8.5-12.5' fill='none' stroke='black' stroke-width='2.4' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E");
          mask-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 18 18'%3E%3Cpath d='M2.5 9.5c1.8 1.6 3.4 3.4 5 5.5 2.4-5 5.4-9 8.5-12.5' fill='none' stroke='black' stroke-width='2.4' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E");
}
.label-red { font: 600 0.72rem/1 var(--f-mono); letter-spacing: 0.12em; text-transform: uppercase; color: var(--red); }
.label-green { font: 600 0.72rem/1 var(--f-mono); letter-spacing: 0.12em; text-transform: uppercase; color: var(--green); }

/* quote from the course */
.pull {
  margin: 1.6rem 0; padding: 4px 0 4px 20px; border-left: 4px solid var(--ink);
  font: 700 1.5rem/1.15 var(--f-display); font-stretch: 80%;
}
.pull cite { display: block; margin-top: 8px; font: 400 0.8rem/1.3 var(--f-mono); color: var(--ink-3); font-style: normal; font-stretch: normal; }

/* two-column split inside a chapter */
.split { display: grid; grid-template-columns: minmax(0, 1fr); gap: 8px 36px; margin: 1.2rem 0; }
@media (min-width: 760px) { .split { grid-template-columns: 1fr 1fr; } }
.split h4 { margin-top: 0.4rem; }

/* sheet: a piece of paper lying on the notebook */
.sheet { background: var(--sheet); border: 1.5px solid var(--rule-strong); box-shadow: var(--shadow); padding: 20px; margin: 1.4rem 0 1.8rem; }
.sheet > :last-child { margin-bottom: 0; }
.sheet__title { display: flex; justify-content: space-between; align-items: baseline; gap: 12px; border-bottom: 1px solid var(--rule); padding-bottom: 10px; margin-bottom: 14px; }
.sheet__title h4 { margin: 0; font-size: 1.25rem; }

/* checklist */
.checklist { list-style: none; padding: 0; margin: 0; }
.checklist li { margin: 0; border-bottom: 1px dashed var(--rule); }
.checklist li:last-child { border-bottom: 0; }
.checklist label { display: grid; grid-template-columns: 28px 1fr; gap: 10px; padding: 9px 0; cursor: pointer; align-items: start; }
.checklist input { appearance: none; -webkit-appearance: none; width: 22px; height: 22px; margin: 2px 0 0; border: 1.5px solid var(--ink); border-radius: 3px 5px 4px 6px; background: var(--paper); cursor: pointer; display: grid; place-items: center; }
.checklist input::after { content: ""; width: 14px; height: 14px; background: var(--green); transform: scale(0); transition: transform 0.12s;
  -webkit-mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 18 18'%3E%3Cpath d='M2.5 9.5c1.8 1.6 3.4 3.4 5 5.5 2.4-5 5.4-9 8.5-12.5' fill='none' stroke='black' stroke-width='3' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E") no-repeat center / contain;
          mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 18 18'%3E%3Cpath d='M2.5 9.5c1.8 1.6 3.4 3.4 5 5.5 2.4-5 5.4-9 8.5-12.5' fill='none' stroke='black' stroke-width='3' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E") no-repeat center / contain; }
.checklist input:checked::after { transform: scale(1.25); }
.checklist .hint { display: block; font-size: 0.85rem; color: var(--ink-3); }
.meter { height: 10px; border: 1.5px solid var(--ink); background: var(--paper); margin: 4px 0 8px; position: relative; overflow: hidden; }
.meter i { position: absolute; inset: 0 auto 0 0; width: 0; background: var(--hl); border-right: 1.5px solid var(--ink); transition: width 0.25s; }
.verdict { font-family: var(--f-hand); color: var(--blue); font-size: 1.15rem; min-height: 1.5em; margin: 6px 0 0; }

/* calculator */
.calc__grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(92px, 1fr)); gap: 10px; margin: 0 0 16px; }
.field { display: flex; flex-direction: column; gap: 4px; }
.field span { font: 500 0.72rem/1 var(--f-mono); color: var(--ink-2); letter-spacing: 0.04em; }
.field input {
  width: 100%; font: 600 1.05rem/1 var(--f-mono); color: var(--ink);
  background: transparent; border: 0; border-bottom: 1.5px solid var(--ink); padding: 8px 2px 6px; border-radius: 0;
}
.field input:focus { outline: none; background: color-mix(in srgb, var(--hl) 35%, transparent); }
.field input::placeholder { color: var(--ink-3); font-weight: 400; }
.calc__sub { font: 600 0.72rem/1 var(--f-mono); letter-spacing: 0.12em; text-transform: uppercase; color: var(--ink-3); margin: 18px 0 10px; }
.calc__out { display: grid; grid-template-columns: minmax(0, 1fr); gap: 16px; margin-top: 20px; padding-top: 18px; border-top: 1.5px solid var(--rule-strong); }
@media (min-width: 640px) { .calc__out { grid-template-columns: repeat(3, minmax(0, 1fr)); } }
.out dt { font: 500 0.7rem/1.2 var(--f-mono); letter-spacing: 0.1em; text-transform: uppercase; color: var(--ink-3); }
.out dd { margin: 4px 0 0; font: 800 2.1rem/1 var(--f-display); font-stretch: 72%; }
.out dd small { display: block; font: 400 0.82rem/1.35 var(--f-body); color: var(--ink-2); margin-top: 6px; font-stretch: normal; }
.stamp {
  display: inline-block; margin-top: 4px;
  font: 800 1.05rem/1 var(--f-display); font-stretch: 85%; letter-spacing: 0.08em; text-transform: uppercase;
  padding: 7px 10px 6px; border: 2.5px double currentColor; transform: rotate(-3deg);
}
.stamp--ok { color: var(--green); }
.stamp--no { color: var(--red); }
.stamp--wait { color: var(--ink-3); }
.btnrow { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 8px; }
.btn { font: 600 0.8rem/1 var(--f-mono); padding: 10px 14px; border: 1.5px solid var(--ink); background: var(--ink); color: var(--paper); cursor: pointer; border-radius: 0; }
.btn--ghost { background: transparent; color: var(--ink); }
.btn:hover { filter: brightness(1.15); }
.btn--ghost:hover { background: var(--ink); color: var(--paper); filter: none; }

/* links list */
.links { list-style: none; padding: 0; margin: 1rem 0 1.8rem; border-top: 1.5px solid var(--rule-strong); }
.links li { margin: 0; border-bottom: 1px solid var(--rule); }
.links a { display: block; position: relative; padding: 12px 36px 12px 2px; text-decoration: none; color: var(--ink); }
.links b { font-weight: 600; }
.links em { display: block; font-style: normal; font-size: 0.9rem; color: var(--ink-2); margin-top: 2px; }
.links .url { display: block; font: 400 0.74rem/1.3 var(--f-mono); color: var(--blue); overflow-wrap: anywhere; margin-top: 3px; }
.links .arr { position: absolute; right: 6px; top: 50%; transform: translateY(-50%); font: 400 1.2rem/1 var(--f-mono); color: var(--ink-3); transition: transform 0.15s, color 0.15s; }
/* Hover: underline the title and nudge the arrow. Nothing painted behind the text, so both themes stay readable. */
.links a:hover b { text-decoration: underline; text-decoration-thickness: 2px; text-underline-offset: 3px; }
.links a:hover .arr { color: var(--ink); transform: translate(4px, -50%); }
.tag { display: inline-block; font: 600 0.64rem/1 var(--f-mono); letter-spacing: 0.08em; text-transform: uppercase; padding: 3px 5px; border: 1px solid var(--ink-3); color: var(--ink-2); vertical-align: 2px; margin-left: 6px; }

/* links with two actions: open the tool, read its source */
.links--dual li { display: grid; grid-template-columns: minmax(0, 1fr) auto; gap: 10px 20px; align-items: center; padding: 14px 2px; }
.links--dual li > div b { font-weight: 600; }
.links--dual li > div em { display: block; margin-top: 2px; }
.links__go { display: flex; flex-wrap: wrap; gap: 8px; margin: 0; }
.links--dual .links__go a {
  display: inline-flex; align-items: center; gap: 6px; padding: 9px 11px;
  font: 600 0.74rem/1 var(--f-mono); white-space: nowrap; text-decoration: none;
  color: var(--ink); border: 1.5px solid var(--ink); background: transparent;
}
.links--dual .links__go a:first-child { background: var(--ink); color: var(--paper); }
.links--dual .links__go a:hover { background: var(--hl); color: var(--hl-ink); border-color: var(--hl-ink); }
@media (max-width: 640px) { .links--dual li { grid-template-columns: minmax(0, 1fr); } }

/* FAQ */
.faqtools { display: flex; flex-wrap: wrap; gap: 10px; align-items: center; margin: 1rem 0 0.6rem; background: var(--paper); padding: 10px 0; z-index: 5; }
@media (min-width: 760px) and (min-height: 640px) { .faqtools { position: sticky; top: 58px; } }
.search { flex: 1 1 260px; display: flex; align-items: center; gap: 8px; border: 1.5px solid var(--ink); background: var(--sheet); padding: 0 10px; }
.search svg { width: 18px; height: 18px; color: var(--ink-3); flex: none; }
.search input { flex: 1; min-width: 0; border: 0; background: transparent; font: 400 1rem/1 var(--f-body); color: var(--ink); padding: 11px 0; }
.search input:focus { outline: none; }
.chips { display: flex; flex-wrap: wrap; gap: 6px; }
.chip { font: 500 0.74rem/1 var(--f-mono); padding: 7px 9px; border: 1px solid var(--rule-strong); background: transparent; color: var(--ink); cursor: pointer; border-radius: 0; }
.chip[aria-pressed="true"] { background: var(--ink); color: var(--paper); }
.faqcount { font: 400 0.8rem/1 var(--f-mono); color: var(--ink-3); margin: 0 0 8px; }
.faq { border-top: 1.5px solid var(--rule-strong); }
.faq details { border-bottom: 1px solid var(--rule); }
.faq summary {
  list-style: none; cursor: pointer; padding: 14px 36px 14px 0; position: relative;
  font-weight: 600; line-height: 1.4;
}
.faq summary::-webkit-details-marker { display: none; }
.faq summary::after { content: "+"; position: absolute; right: 6px; top: 10px; font: 400 1.5rem/1 var(--f-mono); color: var(--ink-3); }
.faq details[open] summary::after { content: "\2212"; color: var(--ink); }
.faq summary .tag { margin-left: 8px; }
.faq .ans { padding: 0 0 16px; color: var(--ink-2); max-width: var(--measure); }
.faq .ans p:last-child { margin-bottom: 0; }
.faq__empty { padding: 20px 0; font-family: var(--f-hand); color: var(--blue); font-size: 1.15rem; }

/* footer */
.foot { border-top: 1.5px solid var(--rule-strong); background: var(--paper-2); }
.foot__in { max-width: 1240px; margin: 0 auto; padding: 34px var(--gutter) 40px; display: grid; gap: 22px; grid-template-columns: minmax(0, 1fr); }
@media (min-width: 860px) { .foot__in { grid-template-columns: 1.3fr 1fr; } }
.foot h2 { font-size: 2rem; font-weight: 820; }
.foot p { color: var(--ink-2); font-size: 0.95rem; }
.foot .sign { font-family: var(--f-hand); color: var(--blue); font-size: 1.35rem; }
.foot small { color: var(--ink-3); }

/* ---------- free AI credits: a coupon cut out of a newspaper ---------- */

.coupon {
  --cut: var(--paper);
  position: relative; display: grid; grid-template-columns: 150px minmax(0, 1fr);
  margin: 0.6rem 0 2rem; background: var(--sheet);
  border: 2px dashed var(--ink);
  box-shadow: var(--shadow);
}
/* scissors on the dashed line */
.coupon::before {
  content: ""; position: absolute; top: -11px; left: 22px; width: 22px; height: 20px;
  background: var(--ink);
  -webkit-mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 22'%3E%3Ccircle cx='5' cy='5' r='3.2' fill='none' stroke='black' stroke-width='2'/%3E%3Ccircle cx='5' cy='17' r='3.2' fill='none' stroke='black' stroke-width='2'/%3E%3Cpath d='M7.6 6.8 22 17M7.6 15.2 22 5' stroke='black' stroke-width='2' stroke-linecap='round'/%3E%3C/svg%3E") no-repeat center / contain;
          mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 22'%3E%3Ccircle cx='5' cy='5' r='3.2' fill='none' stroke='black' stroke-width='2'/%3E%3Ccircle cx='5' cy='17' r='3.2' fill='none' stroke='black' stroke-width='2'/%3E%3Cpath d='M7.6 6.8 22 17M7.6 15.2 22 5' stroke='black' stroke-width='2' stroke-linecap='round'/%3E%3C/svg%3E") no-repeat center / contain;
}
.coupon__stub {
  position: relative; display: flex; flex-direction: column; justify-content: center; align-items: flex-start;
  padding: 18px 16px; background: var(--hl); color: var(--hl-ink);
  border-right: 2px dashed var(--hl-ink);
}
/* punched notches where the stub tears off */
.coupon__stub::before, .coupon__stub::after {
  content: ""; position: absolute; right: -11px; width: 20px; height: 20px; border-radius: 50%;
  background: var(--cut); border: 2px dashed var(--ink);
}
.coupon__stub::before { top: -11px; }
.coupon__stub::after { bottom: -11px; }
.coupon__up { font: 600 0.7rem/1 var(--f-mono); letter-spacing: 0.12em; text-transform: uppercase; }
.coupon__amt { font: 850 3.3rem/0.9 var(--f-display); font-stretch: 70%; letter-spacing: -0.03em; margin: 4px 0 6px; }
.coupon__what { font: 700 0.95rem/1.1 var(--f-display); font-stretch: 85%; text-transform: uppercase; letter-spacing: 0.02em; }
.coupon__body { padding: 18px 20px 16px 26px; min-width: 0; }
.coupon__eyebrow { margin: 0 0 4px; font: 500 0.7rem/1.3 var(--f-mono); letter-spacing: 0.12em; text-transform: uppercase; color: var(--ink-3); }
.coupon__title { margin: 0 0 8px; font: 800 1.45rem/1.05 var(--f-display); font-stretch: 78%; }
.coupon__text { margin: 0 0 12px; font-size: 0.95rem; color: var(--ink-2); }
.coupon__go { display: flex; flex-wrap: wrap; gap: 8px; margin: 0 0 12px; }
.coupon__btn {
  display: inline-flex; align-items: center; gap: 6px; padding: 10px 12px;
  font: 600 0.78rem/1 var(--f-mono); text-decoration: none; white-space: nowrap;
  background: var(--ink); color: var(--paper); border: 1.5px solid var(--ink);
}
.coupon__btn--ghost { background: transparent; color: var(--ink); }
.coupon__btn:hover { background: var(--hl); color: var(--hl-ink); border-color: var(--hl-ink); }
.coupon__fine { list-style: none; margin: 0; padding: 10px 0 0; border-top: 1px dashed var(--rule); }
.coupon__fine li { position: relative; margin: 4px 0; padding-left: 16px; font-size: 0.8rem; line-height: 1.45; color: var(--ink-2); }
.coupon__fine li::before { content: "*"; position: absolute; left: 2px; top: 0; color: var(--red); font-weight: 700; }
@media (max-width: 600px) {
  .coupon { grid-template-columns: minmax(0, 1fr); }
  .coupon__stub { flex-direction: row; align-items: baseline; flex-wrap: wrap; gap: 4px 10px; border-right: 0; border-bottom: 2px dashed var(--hl-ink); }
  .coupon__stub::before, .coupon__stub::after { top: auto; bottom: -11px; right: auto; }
  .coupon__stub::before { left: -11px; }
  .coupon__stub::after { right: -11px; }
  .coupon__amt { font-size: 2.6rem; margin: 0; }
  .coupon__body { padding: 16px; }
}

/* the ticket stub pinned to the corner of the screen */
.ticket {
  position: fixed; right: 16px; bottom: 16px; z-index: 45;
  transform: rotate(-3deg); transform-origin: bottom right;
  transition: opacity 0.2s, transform 0.2s;
}
.ticket[hidden] { display: none; }
.ticket.is-away { opacity: 0; pointer-events: none; transform: rotate(-3deg) translateY(12px); }
.ticket__open {
  display: grid; grid-template-columns: auto auto; align-items: center; gap: 2px 10px;
  padding: 10px 14px 10px 18px; cursor: pointer;
  background: var(--hl); color: var(--hl-ink); border: 2px solid var(--hl-ink);
  /* perforated left edge */
  -webkit-mask: radial-gradient(circle at 0 50%, transparent 5px, #000 5.5px) left / 10px 14px repeat-y, linear-gradient(#000, #000) 5px 0 / calc(100% - 5px) 100% no-repeat;
          mask: radial-gradient(circle at 0 50%, transparent 5px, #000 5.5px) left / 10px 14px repeat-y, linear-gradient(#000, #000) 5px 0 / calc(100% - 5px) 100% no-repeat;
  box-shadow: 0 10px 22px -12px rgba(0, 0, 0, 0.6);
}
.ticket__open:hover { transform: translateY(-2px); }
.ticket__amt { font: 850 1.9rem/0.9 var(--f-display); font-stretch: 70%; letter-spacing: -0.02em; }
.ticket__what { font: 700 0.72rem/1.05 var(--f-mono); text-transform: uppercase; letter-spacing: 0.06em; text-align: left; }
.ticket__x {
  position: absolute; top: -10px; left: -10px; width: 24px; height: 24px; display: grid; place-items: center;
  border-radius: 50%; border: 1.5px solid var(--ink); background: var(--paper); color: var(--ink);
  font: 400 16px/1 var(--f-mono); cursor: pointer; padding: 0;
}
@media (prefers-reduced-motion: no-preference) {
  .ticket.is-new .ticket__open { animation: ticket-nudge 0.9s ease-in-out 2; }
}
@media (max-width: 600px) {
  .ticket { right: 12px; bottom: 12px; }
  .ticket__open { padding: 7px 11px 7px 15px; gap: 2px 8px; }
  .ticket__amt { font-size: 1.45rem; }
  .ticket__what { font-size: 0.6rem; }
  .ticket__x { width: 22px; height: 22px; top: -9px; left: -9px; font-size: 14px; }
  .coupon-dialog .coupon__text { font-size: 0.9rem; }
  .coupon-dialog .coupon__fine li { font-size: 0.76rem; }
}
@keyframes ticket-nudge {
  0%, 100% { transform: rotate(0); }
  25% { transform: rotate(-4deg); }
  75% { transform: rotate(3deg); }
}

.coupon-dialog {
  width: min(760px, calc(100vw - 32px)); max-height: calc(100vh - 48px); max-height: calc(100dvh - 32px); overflow: auto;
  padding: 0; border: 0; background: transparent; color: var(--ink);
}
.coupon-dialog::backdrop { background: rgba(10, 11, 14, 0.82); backdrop-filter: blur(3px); -webkit-backdrop-filter: blur(3px); }
.coupon-dialog__bar { display: flex; justify-content: space-between; align-items: center; margin-bottom: 14px; }
.coupon-dialog__title { margin: 0; font: 600 0.8rem/1 var(--f-mono); letter-spacing: 0.14em; text-transform: uppercase; color: #f6f6f1; }
.coupon-dialog__close {
  width: 36px; height: 36px; display: grid; place-items: center; cursor: pointer; padding: 0;
  font: 400 22px/1 var(--f-mono); color: #16181d; background: #f6f6f1; border: 1.5px solid #16181d;
}
.coupon-dialog .coupon { margin: 12px 0 4px; --cut: var(--sheet); }
.coupon-dialog .coupon::before { background: #f6f6f1; }
/* over the dark backdrop a punched hole has nothing sensible to show, so drop the notches there */
.coupon-dialog .coupon__stub::before, .coupon-dialog .coupon__stub::after { display: none; }

/* print: it is a handbook, people will print it */
@media print {
  body { background: #fff; color: #000; font-size: 11pt; }
  .topbar, .toc, .toc-m, .faqtools, .btnrow, .term__scroll, .ticket, .coupon-dialog { display: none !important; }
  .book { display: block; }
  .faq details { break-inside: avoid; }
  .faq details:not([open]) .ans { display: block; }
  .note { float: none; margin: 0.4rem 0; transform: none; }
}