/* COBOL Textbook: "the mainframe manual". IBM Plex Serif for reading, Plex Sans for headings and the interface,
   Plex Mono for listings. White page, ink rules, numbered parts and sections, listings on green-bar bands. */

:root {
  --ink: #161616;
  --muted: #525252;
  --rule: #D0D0D0;
  --green: #2B6A3E;
  --bar: #E8F3EA;
  --link: #1C4E80;
  --wrap: 1200px;
  --gut: clamp(16px, 4vw, 40px);
  --serif: "IBM Plex Serif", Georgia, "Times New Roman", serif;
  --sans: "IBM Plex Sans", "Helvetica Neue", sans-serif;
  --mono: "IBM Plex Mono", Consolas, "Courier New", monospace;
}

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body { margin: 0; background: #FFFFFF; color: var(--ink); font-family: var(--serif); font-size: 18px; line-height: 1.65; }
a { color: var(--link); text-underline-offset: 0.15em; }
a:hover { color: var(--green); }
:focus-visible { outline: 2px solid var(--link); outline-offset: 2px; }
.wrap { max-width: var(--wrap); margin: 0 auto; padding-left: var(--gut); padding-right: var(--gut); }
.table-scroll { overflow-x: auto; }
.num { text-align: right; font-variant-numeric: tabular-nums; }

/* ---- masthead ---- */
.masthead { border-bottom: 1px solid var(--ink); }
.masthead-row { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 12px 40px;
  padding-top: 18px; padding-bottom: 18px; }
.wordmark { display: inline-flex; align-items: center; gap: 12px; color: var(--ink); text-decoration: none; }
.wordmark:hover { color: var(--ink); }
.wordmark .mark { width: 22px; height: 28px; flex: 0 0 auto; display: block; }
.wordmark-name { font-family: var(--sans); font-size: 21px; line-height: 1; font-weight: 400; }
.wordmark-name b, .foot-name b { font-weight: 700; }
.site-nav { display: flex; flex-wrap: wrap; gap: 0 28px; font-family: var(--sans); font-size: 16px; }
.site-nav a { color: var(--ink); text-decoration: none; padding: 8px 0; }
.site-nav a:hover { color: var(--green); text-decoration: underline; }
.site-nav a[aria-current="page"] { font-weight: 600; }

/* ---- home: title page ---- */
.title-grid { display: flex; flex-wrap: wrap; gap: 48px 72px; align-items: flex-start; padding-top: 64px; }
.title-main { flex: 7 1 520px; min-width: 0; }
.title-main h1 { margin: 0; font-family: var(--sans); font-weight: 600; font-size: clamp(36px, 4.4vw, 56px); line-height: 1.05;
  letter-spacing: -0.02em; }
.title-main .lede { margin: 24px 0 0; max-width: 34em; font-size: clamp(18px, 1.6vw, 21px); line-height: 1.55; }
.front-matter { margin: 40px 0 0; display: grid; grid-template-columns: repeat(auto-fit, minmax(210px, 1fr)); border-top: 1px solid var(--ink);
  font-family: var(--sans); }
.front-matter div { padding: 12px 24px 12px 0; border-bottom: 1px solid var(--rule); }
.front-matter dt { font-size: 14px; color: var(--muted); }
.front-matter dd { margin: 4px 0 0; font-size: 17px; font-weight: 500; }
.changes { flex: 5 1 340px; min-width: 0; }
.changes h2 { margin: 0; font-family: var(--sans); font-weight: 600; font-size: 20px; line-height: 1.3; }
.changes-note { margin: 4px 0 0; font-family: var(--sans); font-size: 15px; color: var(--muted); }
.change-list { list-style: none; margin: 16px 0 0; padding: 0; border-top: 1px solid var(--ink); }
.change-list li { display: grid; grid-template-columns: 96px minmax(0, 1fr); gap: 4px 16px; padding: 12px 0; border-bottom: 1px solid var(--rule); }
.change-list time { font-family: var(--sans); font-size: 15px; line-height: 1.55; color: var(--muted); font-variant-numeric: tabular-nums; }
.change-list span { font-size: 17px; line-height: 1.5; }
.change-list a, .toc a, .guide-list a, .crumbs a, .site-foot li a, .entry-main h3 a, .part-head h3 a, .part-row h2 a { text-decoration: none; }
.change-list a:hover, .toc a:hover, .guide-list a:hover, .crumbs a:hover, .site-foot li a:hover, .entry-main h3 a:hover,
.part-head h3 a:hover, .part-row h2 a:hover { text-decoration: underline; }
.changes-links { margin: 16px 0 0; font-family: var(--sans); font-size: 15px; }

/* ---- home: contents ---- */
.contents > .wrap { padding-top: 72px; }
.contents-head { display: flex; flex-wrap: wrap; align-items: baseline; justify-content: space-between; gap: 8px 32px; margin: 0 0 24px; }
.contents-head h2 { margin: 0; font-family: var(--sans); font-weight: 600; font-size: 36px; line-height: 1.15; letter-spacing: -0.01em; }
.contents-head p { margin: 0; font-family: var(--sans); font-size: 15px; color: var(--muted); }
.part { display: flex; flex-wrap: wrap; gap: 12px 64px; padding: 16px 0 28px; border-top: 2px solid var(--ink); }
.part-head { flex: 0 1 300px; min-width: 0; }
.part-head h3 { margin: 0; display: flex; gap: 14px; align-items: baseline; font-family: var(--sans); font-weight: 600; font-size: 22px; line-height: 1.3; }
.part-head h3 a { color: var(--ink); }
.part-no { color: var(--green); font-variant-numeric: tabular-nums; }
.part-blurb { margin: 6px 0 0; font-style: italic; font-size: 15px; line-height: 1.5; color: var(--muted); }
.part-count { margin: 6px 0 0; font-family: var(--sans); font-size: 14px; color: var(--muted); }
.toc { flex: 1 1 560px; min-width: 0; list-style: none; margin: 0; padding: 0; }
.toc li { display: flex; align-items: flex-end; gap: 10px; padding: 5px 0; }
.toc-no { flex: 0 0 34px; align-self: flex-start; font-family: var(--sans); font-weight: 500; font-size: 15px; line-height: 27px;
  color: var(--green); font-variant-numeric: tabular-nums; }
.toc a { flex: 0 1 auto; min-width: 0; font-size: 17px; line-height: 27px; }
.toc-leader { flex: 1 0 32px; margin-bottom: 8px; border-bottom: 2px dotted var(--rule); }
.toc-time { flex: 0 0 auto; min-width: 52px; white-space: nowrap; text-align: right; font-family: var(--sans); font-size: 15px; line-height: 27px; color: var(--muted);
  font-variant-numeric: tabular-nums; }
.toc-empty { margin: 0; font-family: var(--sans); font-size: 15px; color: var(--muted); }

/* ---- home: about ---- */
.home-about > .wrap { padding-top: 32px; }
.about-grid { display: flex; flex-wrap: wrap; gap: 16px 64px; padding-top: 24px; border-top: 2px solid var(--ink); }
.about-grid h2 { flex: 1 1 220px; margin: 0; font-family: var(--sans); font-weight: 600; font-size: 24px; line-height: 1.3; }
.about-body { flex: 3 1 560px; min-width: 0; max-width: 700px; }
.about-body p { margin: 0 0 24px; font-size: 18px; line-height: 1.7; }
.note { margin: 32px 0; padding: 16px 0; border-top: 1px solid var(--rule); border-bottom: 1px solid var(--rule); }
.note p { margin: 0; font-size: 17px; line-height: 1.65; }
.note strong { font-family: var(--sans); font-weight: 600; }

/* ---- lesson ---- */
.crumbs { border-bottom: 1px solid var(--rule); }
.crumbs-row { display: flex; flex-wrap: wrap; justify-content: space-between; gap: 4px 24px; padding-top: 12px; padding-bottom: 12px;
  font-family: var(--sans); font-size: 14px; color: var(--muted); }
.crumbs-row p { margin: 0; }
.lesson-head { padding-top: 56px; }
.lesson-title { display: flex; flex-wrap: wrap; gap: 4px 28px; align-items: baseline; }
.lesson-no, .lesson-title h1 { margin: 0; font-family: var(--sans); font-weight: 600; font-size: clamp(30px, 4vw, 46px); line-height: 1.12;
  letter-spacing: -0.015em; }
.lesson-no { flex: 0 0 auto; color: var(--green); font-variant-numeric: tabular-nums; }
.lesson-title h1 { flex: 1 1 560px; min-width: 0; max-width: 20em; }
.lesson-head .lede { margin: 20px 0 0; max-width: 36em; font-size: 21px; line-height: 1.5; }
.lesson-meta { margin: 28px 0 0; padding: 12px 0; border-top: 1px solid var(--ink); border-bottom: 1px solid var(--rule);
  display: flex; flex-wrap: wrap; gap: 6px 36px; font-family: var(--sans); font-size: 15px; }
.lesson-meta div { display: flex; gap: 8px; align-items: baseline; }
.lesson-meta dt { color: var(--muted); }
.lesson-meta dd { margin: 0; font-weight: 500; }
.review-line { margin: 12px 0 0; font-family: var(--sans); font-size: 15px; color: var(--muted); }
.lesson-grid { display: flex; flex-wrap: wrap; gap: 48px 64px; align-items: flex-start; padding-top: 16px; }
.lesson-body { flex: 1 1 560px; min-width: 0; max-width: 640px; padding-top: 24px; }
.lesson-guide { flex: 0 1 300px; min-width: 0; padding-top: 24px; font-family: var(--sans); font-size: 15px; line-height: 1.45; }

/* ---- prose ---- */
.prose p { margin: 0 0 22px; font-size: 17px; line-height: 1.65; }
.prose li { font-size: 17px; line-height: 1.6; margin: 6px 0; }
.prose ul, .prose ol { margin: 0 0 22px; padding-left: 1.4em; }
.prose h2 { margin: 48px 0 18px; padding-top: 14px; border-top: 1px solid var(--ink); font-family: var(--sans); font-weight: 600;
  font-size: 26px; line-height: 1.25; }
.prose h2[data-n]::before { content: attr(data-n); margin-right: 16px; color: var(--green); font-variant-numeric: tabular-nums; }
.prose h3 { margin: 32px 0 12px; font-family: var(--sans); font-weight: 600; font-size: 20px; line-height: 1.3; }
.prose code { font-family: var(--mono); font-size: 0.88em; overflow-wrap: anywhere; }
.prose strong { font-weight: 600; }
.prose blockquote { margin: 28px 0; padding: 16px 20px; border: 1px solid var(--ink); }
.prose blockquote p:last-child { margin-bottom: 0; }
.prose hr { border: 0; border-top: 1px solid var(--rule); margin: 32px 0; }
.table-fig { margin: 32px 0; }
.table-fig figcaption, .listing figcaption { font-family: var(--sans); font-size: 15px; line-height: 1.5; }
.table-fig figcaption { margin: 0 0 10px; }
.table-fig strong, .listing figcaption strong { font-weight: 600; }
.prose table { width: 100%; min-width: 520px; border-collapse: collapse; font-family: var(--sans); font-size: 15px; font-variant-numeric: tabular-nums; }
.prose th { padding: 6px 14px 6px 0; font-weight: 600; font-size: 14px; text-align: left; vertical-align: bottom; border-bottom: 1px solid var(--ink); }
.prose td { padding: 6px 14px 6px 0; vertical-align: top; line-height: 1.45; border-bottom: 1px solid var(--rule); }
.prose th:last-child, .prose td:last-child { padding-right: 0; }
.prose td code { font-size: 14px; }
.prose .num { text-align: right; }

/* listings: green-bar bands three lines deep, line numbers from the source file */
.listing { position: relative; margin: 36px 0 32px; }
.listing .highlight { overflow-x: auto; border-top: 1px solid var(--ink); border-bottom: 1px solid var(--ink); }
.highlight pre { margin: 0; padding: 0; font-family: var(--mono); font-size: 14px; line-height: 22px; color: var(--ink); }
.highlight code { font-family: inherit; font-size: inherit; overflow-wrap: normal; }
.listing pre { display: inline-block; min-width: 100%; vertical-align: top; padding-right: 24px;
  background-image: repeating-linear-gradient(to bottom, var(--bar) 0, var(--bar) 66px, #FFFFFF 66px, #FFFFFF 132px); }
.listing .ln::before { counter-increment: ln; content: counter(ln); display: inline-block; width: 60px; padding-right: 16px;
  text-align: right; color: var(--muted); font-variant-numeric: tabular-nums; -webkit-user-select: none; user-select: none; }
.listing figcaption { margin-top: 10px; }
.listing--cmd pre { padding: 8px 12px; background: none; }
.listing--cmd .ln::before { content: none; }
/* the copy button (js/common.js) sits above the listing's top rule, never over the code */
.listing .copy-btn { position: absolute; top: -28px; right: 0; float: none !important; margin: 0 !important;
  background: #FFFFFF !important; font-family: var(--sans) !important; }
.prose .nw { white-space: nowrap; }

/* code token colours (Pygments classes): ink keywords, blue literals, grey comments */
.highlight .k, .highlight .kc, .highlight .kd, .highlight .kn, .highlight .kp, .highlight .kr, .highlight .kt, .highlight .ow { color: #161616; font-weight: 500; }
.highlight .s, .highlight .s1, .highlight .s2, .highlight .sa, .highlight .sb, .highlight .sc, .highlight .sd, .highlight .se,
.highlight .sh, .highlight .si, .highlight .sr, .highlight .ss, .highlight .sx, .highlight .dl { color: #1C4E80; }
.highlight .m, .highlight .mb, .highlight .mf, .highlight .mh, .highlight .mi, .highlight .il, .highlight .mo { color: #1C4E80; }
.highlight .c, .highlight .c1, .highlight .ch, .highlight .cm, .highlight .cp, .highlight .cpf, .highlight .cs { color: #525252; }
.highlight .nf, .highlight .fm, .highlight .nc { font-weight: 500; }
.highlight .nb, .highlight .bp, .highlight .nt { color: #2B6A3E; }
.highlight .err { color: inherit; background: none; border: 0; }

/* lesson guide (the right-hand column) */
.guide-block { margin: 0 0 40px; }
.guide-h { margin: 0 0 8px; padding-bottom: 8px; border-bottom: 1px solid var(--ink); font-family: var(--sans); font-weight: 600; font-size: 16px; line-height: 1.4; }
.guide-list { list-style: none; margin: 0; padding: 0; }
.guide-list li { display: flex; gap: 12px; padding: 7px 0; border-bottom: 1px solid var(--rule); }
.toc-n { flex: 0 0 46px; color: var(--green); font-variant-numeric: tabular-nums; }
.is-current { font-weight: 600; }
.files-box ul { list-style: none; margin: 0; padding: 0; }
.files-box li { padding: 8px 0; border-bottom: 1px solid var(--rule); overflow-wrap: anywhere; font-size: 14px; color: var(--muted); }
.files-box a { font-family: var(--mono); font-size: 14px; }
.sources ol { margin: 0; padding-left: 22px; font-size: 13px; line-height: 1.45; }
.sources li { margin: 0 0 10px; padding-left: 2px; overflow-wrap: anywhere; }
.tag-row { margin: 32px 0 0; font-family: var(--sans); font-size: 14px; color: var(--muted); }
.tag-label { margin-right: 6px; font-weight: 600; color: var(--ink); }
.honesty-note { margin: 24px 0; padding: 16px 20px; border: 1px solid var(--ink); font-size: 16px; }
.prev-next { margin: 24px 0 0; padding-top: 16px; border-top: 1px solid var(--ink); display: flex; flex-wrap: wrap; justify-content: space-between;
  gap: 16px 32px; font-family: var(--sans); font-size: 15px; line-height: 1.5; }
.prev-next p { margin: 0; flex: 1 1 260px; }
.pn-next { text-align: right; }
.pn-label { display: block; color: var(--muted); }

/* ---- index pages ---- */
.index-head { padding-top: 56px; }
.index-head h1 { margin: 0; font-family: var(--sans); font-weight: 600; font-size: clamp(32px, 4vw, 46px); line-height: 1.12; letter-spacing: -0.015em; }
.index-head .lede { margin: 16px 0 0; max-width: 40em; font-size: 19px; line-height: 1.55; }
.part-label { margin: 0 0 6px; font-family: var(--sans); font-size: 15px; font-weight: 600; color: var(--green); }
.index-body { padding-top: 24px; }
.month h2 { margin: 32px 0 0; padding-top: 10px; border-top: 2px solid var(--ink); font-family: var(--sans); font-weight: 600; font-size: 24px; line-height: 1.3; }
.entries { list-style: none; margin: 0; padding: 0; }
.entry { display: grid; grid-template-columns: 120px 48px minmax(0, 1fr) 64px; gap: 4px 20px; align-items: baseline; padding: 16px 0;
  border-bottom: 1px solid var(--rule); }
.entry-meta { margin: 0; font-family: var(--sans); font-size: 14px; line-height: 1.5; color: var(--muted); }
.entry-meta time { display: block; }
.entry-no { margin: 0; font-family: var(--sans); font-weight: 600; color: var(--green); font-variant-numeric: tabular-nums; }
.entry-main h3 { margin: 0; font-family: var(--sans); font-weight: 600; font-size: 19px; line-height: 1.35; }
.entry-desc { margin: 4px 0 0; font-size: 16px; line-height: 1.55; }
.entry-time { margin: 0; text-align: right; font-family: var(--sans); font-size: 14px; color: var(--muted); }
.part-list { list-style: none; margin: 0; padding: 0; }
.part-row { display: flex; gap: 24px; padding: 20px 0; border-top: 2px solid var(--ink); }
.part-row .part-no { flex: 0 0 40px; margin: 0; font-family: var(--sans); font-weight: 600; font-size: 28px; line-height: 1.2; }
.part-row h2 { margin: 0; font-family: var(--sans); font-weight: 600; font-size: 24px; line-height: 1.3; }
.part-row h2 a { color: var(--ink); }
.part-row p { margin: 6px 0 0; }
.part-row .small { font-family: var(--sans); font-size: 14px; color: var(--muted); }

/* ---- documents (about, how, contact, privacy, terms, 404) ---- */
.doc { padding-top: 56px; }
.doc-body { max-width: 720px; }
.doc-body h1 { margin: 0 0 20px; font-family: var(--sans); font-weight: 600; font-size: clamp(32px, 4vw, 46px); line-height: 1.12; letter-spacing: -0.015em; }
.doc-body h2 { margin: 40px 0 12px; padding-top: 12px; border-top: 1px solid var(--ink); font-family: var(--sans); font-weight: 600; font-size: 24px; line-height: 1.3; }
.doc-body p, .doc-body li { font-size: 18px; line-height: 1.7; }
.doc-body p { margin: 0 0 20px; }
.doc-body ul, .doc-body ol { margin: 0 0 20px; padding-left: 1.4em; }
.doc-body .lede { font-size: 21px; line-height: 1.5; }
.doc-body .small { font-family: var(--sans); font-size: 15px; color: var(--muted); }
.doc-body code { font-family: var(--mono); font-size: 0.88em; }
.card { margin: 24px 0; padding: 16px 0 0; border-top: 1px solid var(--rule); border-bottom: 1px solid var(--rule); }
.editor-box { margin: 32px 0; padding: 4px 24px 8px; border: 1px solid var(--ink); }
.doc-body .editor-box h2 { margin: 16px 0 8px; padding-top: 0; border-top: 0; font-size: 20px; }

/* ---- footer ---- */
.site-foot { margin-top: 80px; border-top: 2px solid var(--ink); font-family: var(--sans); font-size: 15px; line-height: 1.5; }
.foot-grid { display: flex; flex-wrap: wrap; gap: 32px 64px; padding-top: 40px; padding-bottom: 32px; }
.foot-brand { flex: 2 1 340px; min-width: 0; }
.foot-name { margin: 0 0 12px; font-size: 19px; }
.foot-brand p { margin: 0 0 12px; max-width: 34em; }
.foot-owner { color: var(--muted); }
.site-foot nav { flex: 1 1 180px; min-width: 0; }
.foot-h { margin: 0 0 12px; font-weight: 600; }
.site-foot ul { list-style: none; margin: 0; padding: 0; }
.site-foot li { margin: 0 0 8px; }
.foot-legal { display: flex; flex-wrap: wrap; justify-content: space-between; gap: 8px 32px; padding: 16px 0 40px; border-top: 1px solid var(--rule);
  font-size: 14px; color: var(--muted); }
.foot-legal p { margin: 0; }
.foot-legal-line { flex: 1 1 520px; max-width: 62em; }

/* ---- small screens ---- */
@media (max-width: 640px) {
  body { font-size: 17px; }
  .title-grid { padding-top: 40px; }
  .contents > .wrap { padding-top: 48px; }
  .contents-head h2 { font-size: 30px; }
  .toc a { font-size: 16px; }
  .toc-time { min-width: 44px; }
  .lesson-head, .index-head, .doc { padding-top: 32px; }
  .lesson-head .lede { font-size: 19px; }
  .prose h2 { font-size: 22px; }
  .entry { grid-template-columns: 40px minmax(0, 1fr); }
  .entry-meta { grid-column: 1 / -1; }
  .entry-meta time { display: inline; margin-right: 8px; }
  .entry-time { grid-column: 2; text-align: left; }
  .listing .ln::before { width: 44px; padding-right: 12px; }
}

/* ---- topic introductions (fix round 2026-10-15, item 4): a 150-300 word intro under each topic head ---- */
.topic-intro { max-width: 40em; margin: 0 0 28px; }
.topic-intro p { margin: 0 0 16px; font-size: 17px; line-height: 1.65; }