:root {
    --paper:#f3f9fa;
    --white:#ffffff;
    --line:#c9dde4;
    --line-bright:#e2eef2;
    --ink:#31566d;
    --ink-soft:#52778d;
    --accent:#117c94;
    --accent-light:#e0f0f3;
    --accent-dark:#216a84;
    --warm:#cb665b;
    --warm-light:#fff0ef;
    --shell:1220px;
    --space:24px;
}
* { box-sizing:border-box; }
html { scroll-behavior:smooth; }
body { margin:0; color:var(--ink); background:var(--paper); font-family:system-ui,-apple-system,"Segoe UI",Roboto,Arial,sans-serif; line-height:1.62; }
a { color:var(--accent-dark); text-underline-offset:3px; }
a:hover { color:var(--warm); }
a:focus-visible, summary:focus-visible { outline:3px solid var(--warm); outline-offset:4px; }
.shell { width:min(calc(100% - 64px),var(--shell)); margin-inline:auto; }
.site-head { background:var(--white); border-bottom:1px solid var(--line); }
.head-line { display:flex; align-items:center; gap:30px; min-height:92px; }
.site-mark { display:flex; align-items:center; gap:13px; text-decoration:none; color:var(--ink); flex-shrink:0; }
.mark-graphic { width:43px; height:43px; border:2px solid var(--accent); display:flex; align-items:flex-end; gap:4px; padding:8px; background:var(--accent-light); }
.mark-graphic span { background:var(--accent); width:6px; }
.mark-graphic span:nth-child(1) { height:15px; }
.mark-graphic span:nth-child(2) { height:24px; }
.mark-graphic span:nth-child(3) { height:19px; }
.mark-name { display:flex; flex-direction:column; font-size:20px; font-weight:800; letter-spacing:.14em; line-height:1.1; }
.mark-name small { margin-top:6px; font-size:10px; font-weight:650; letter-spacing:.1em; color:var(--ink-soft); }
.nav-main { display:flex; flex-wrap:wrap; gap:4px 17px; justify-content:flex-end; margin-left:auto; }
.nav-main a { font-size:13px; font-weight:650; padding:10px 0; text-decoration:none; color:var(--ink-soft); border-bottom:2px solid transparent; white-space:nowrap; }
.nav-main a[aria-current],.nav-main a:hover { border-color:var(--warm); color:var(--ink); }
.mobile-navigation { display:none; }
.service-strip { background:#dbeef3; border-bottom:1px solid #c6e2e9; }
.strip-line { display:flex; justify-content:space-between; gap:20px; padding-block:8px; font-size:10px; letter-spacing:.19em; font-weight:750; color:#46798f; }
.content { padding-block:50px 76px; }
.opening { display:grid; grid-template-columns:minmax(0,1.6fr) minmax(295px,.88fr); align-items:stretch; gap:32px; margin-bottom:52px; }
.opening-copy { padding:6px 0; }
.eyebrow { display:block; color:var(--warm); font-size:11px; letter-spacing:.17em; font-weight:800; margin-bottom:13px; }
h1 { font-size:40px; line-height:1.19; letter-spacing:-.025em; margin:0 0 22px; color:var(--ink); font-weight:800; overflow-wrap:anywhere; }
h2 { font-size:28px; line-height:1.26; letter-spacing:-.024em; margin:0; color:var(--ink); }
h3 { font-size:20px; line-height:1.35; margin:0 0 12px; color:var(--ink); }
p { font-size:16px; margin:0 0 15px; line-height:1.75; }
p:last-child { margin-bottom:0; }
.opening-copy p { max-width:700px; }
.work-sheet { position:relative; border:1px solid var(--line); background:var(--white); border-left:5px solid var(--accent); padding:17px 24px 19px 22px; box-shadow:7px 7px 0 #e2f0f3; }
.work-sheet:after { content:""; position:absolute; left:8px; top:12px; bottom:12px; border-left:1px dotted var(--line); }
.sheet-top { display:flex; justify-content:space-between; align-items:center; color:var(--warm); font-size:11px; letter-spacing:.14em; font-weight:800; padding-bottom:9px; border-bottom:1px solid var(--line); }
.sheet-sign { font-size:23px; line-height:1; color:var(--accent); }
.sheet-list { padding:0; margin:5px 0 0; list-style:none; }
.sheet-list li { border-bottom:1px solid var(--line-bright); padding:12px 0; }
.sheet-list li:last-child { border-bottom:0; padding-bottom:0; }
.quick-label { font-size:11px; font-weight:800; text-transform:uppercase; letter-spacing:.13em; color:var(--accent); display:block; margin-bottom:3px; }
.sheet-list strong { display:block; font-size:14px; line-height:1.4; font-weight:650; color:var(--ink); }
.chapter-stack { border-top:2px solid var(--ink-soft); }
.chapter { padding:30px 0 38px; border-bottom:1px solid var(--line); }
.section-head { display:flex; align-items:baseline; gap:15px; margin:0 0 22px; }
.section-index { flex:0 0 auto; border:1px solid var(--line); background:white; font-size:12px; font-weight:800; color:var(--warm); padding:4px 9px; letter-spacing:.04em; }
.chapter-text { column-count:2; column-gap:42px; column-rule:1px solid var(--line); }
.chapter-text p { break-inside:avoid; }
.data-source { color:var(--ink-soft); font-size:16px; line-height:1.55; padding:11px 15px; border-left:3px solid var(--accent); background:var(--white); margin-top:20px; }
.stages { list-style:none; margin:0; padding:0; display:grid; grid-template-columns:repeat(4,minmax(0,1fr)); border:1px solid var(--line); background:var(--white); }
.stages li { position:relative; padding:18px 16px 22px; border-right:1px solid var(--line); min-width:0; }
.stages li:last-child { border-right:0; }
.stages li:before { content:""; position:absolute; top:0; left:0; width:100%; border-top:4px solid var(--accent); }
.stages li:nth-child(even):before { border-top-color:var(--warm); }
.stage-number { font-size:14px; color:var(--warm); font-weight:850; letter-spacing:.1em; display:block; margin-bottom:11px; }
.stages strong { display:block; font-size:15px; line-height:1.4; margin-bottom:6px; }
.stages p { font-size:16px; line-height:1.55; margin:0; }
.matrix { border-top:2px solid var(--accent); background:var(--white); }
.matrix-row { display:grid; grid-template-columns:minmax(145px,.7fr) minmax(0,1.15fr) minmax(0,1.15fr); gap:16px; align-items:start; padding:17px 20px; border-bottom:1px solid var(--line); font-size:15px; line-height:1.6; }
.matrix-row:nth-child(even) { background:#f0f8fa; }
.matrix-row strong { font-size:15px; color:var(--accent-dark); }
.paired { display:grid; grid-template-columns:repeat(2,minmax(0,1fr)); gap:16px; }
.paired-item { padding:22px 24px 24px; background:var(--white); border-top:3px solid var(--accent); border-bottom:1px solid var(--line); }
.paired-item:nth-child(2) { border-top-color:var(--warm); }
.paired-item p { line-height:1.75; }
.equations { list-style:none; margin:0; padding:0; background:var(--white); border:1px solid var(--line); }
.equations li { display:grid; grid-template-columns:minmax(180px,.8fr) minmax(0,2fr); gap:20px; padding:18px 20px; border-bottom:1px solid var(--line); }
.equations li:last-child { border-bottom:0; }
.equations span { font-weight:750; color:var(--accent); }
.equations strong { font-weight:650; }
.field-notes { list-style:none; margin:0; padding:0; display:grid; grid-template-columns:repeat(3,minmax(0,1fr)); gap:16px; }
.field-notes li { display:flex; align-items:flex-start; gap:15px; padding:18px 18px 20px 0; border-bottom:2px solid var(--line); }
.note-rule { display:block; width:5px; height:33px; flex:0 0 5px; background:var(--warm); }
.field-notes li:nth-child(even) .note-rule { background:var(--accent); }
.field-notes strong { display:block; font-size:15px; line-height:1.5; margin-bottom:7px; }
.field-notes p { font-size:16px; line-height:1.65; margin:0; }
.subject-nav { margin-top:50px; background:var(--white); border:1px solid var(--line); padding:24px 28px; }
.subject-nav h2 { font-size:28px; margin-bottom:20px; }
.subject-nav ul { display:grid; grid-template-columns:repeat(4,minmax(0,1fr)); list-style:none; margin:0; padding:0; gap:0 24px; }
.subject-nav li { border-top:1px solid var(--line-bright); }
.subject-nav a { display:block; padding:9px 1px; font-size:14px; font-weight:650; text-decoration:none; }
.subject-nav a[aria-current] { color:var(--warm); }
.site-footer { background:#dceef2; border-top:1px solid var(--line); padding-block:24px; }
.footer-row { display:flex; gap:18px; align-items:center; }
.footer-row>div:nth-child(2) { display:flex; flex-direction:column; line-height:1.5; margin-right:auto; }
.footer-row strong { letter-spacing:.13em; font-size:16px; }
.footer-row small { letter-spacing:.1em; font-weight:700; font-size:10px; color:var(--ink-soft); }
.footer-row>a { font-size:13px; font-weight:700; text-decoration:none; }
.footer-symbol { display:flex; align-items:end; gap:3px; width:34px; height:34px; padding:7px; border:2px solid var(--accent); }
.footer-symbol i { display:block; width:5px; height:14px; background:var(--accent); }
.footer-symbol i:nth-child(2) { height:20px; }
.footer-symbol i:nth-child(3) { height:10px; }
@media(max-width:1080px) {
    .head-line { gap:20px; }
    .nav-main { gap:3px 10px; }
    .nav-main a { font-size:12px; }
    .opening { grid-template-columns:minmax(0,1.5fr) minmax(250px,.85fr); gap:24px; }
    .stages { grid-template-columns:repeat(2,minmax(0,1fr)); }
    .stages li:nth-child(2) { border-right:0; }
    .stages li:nth-child(-n+2) { border-bottom:1px solid var(--line); }
    .field-notes { grid-template-columns:repeat(2,minmax(0,1fr)); }
    .field-notes li:last-child:nth-child(odd) { grid-column:1/-1; }
}
@media(max-width:790px) {
    .shell { width:min(calc(100% - 38px),var(--shell)); }
    .head-line { min-height:72px; }
    .nav-main { display:none; }
    .mobile-navigation { display:block; margin-left:auto; position:relative; }
    .mobile-navigation summary { cursor:pointer; list-style:none; color:var(--ink); font-size:14px; font-weight:800; padding:8px 12px; border:1px solid var(--line); background:var(--white); }
    .mobile-navigation summary::-webkit-details-marker { display:none; }
    .menu-symbol:after { content:"+"; color:var(--accent); padding-left:8px; }
    .mobile-navigation[open] .menu-symbol:after { content:"−"; }
    .mobile-navigation nav { position:absolute; top:calc(100% + 4px); right:0; z-index:5; width:min(260px,calc(100vw - 38px)); display:flex; flex-direction:column; background:var(--white); box-shadow:0 10px 22px #b9d3db80; border:1px solid var(--line); padding:8px; }
    .mobile-navigation nav a { padding:10px 12px; text-decoration:none; font-weight:650; border-bottom:1px solid var(--line-bright); }
    .mobile-navigation nav a:last-child { border-bottom:0; }
    .content { padding-top:30px; }
    .opening { grid-template-columns:1fr; gap:24px; margin-bottom:34px; }
    .work-sheet { box-shadow:5px 5px 0 #e2f0f3; }
    .sheet-list { display:grid; grid-template-columns:repeat(3,minmax(0,1fr)); gap:16px; }
    .sheet-list li { border-bottom:0; }
    .chapter-text { column-count:1; }
    .subject-nav ul { grid-template-columns:repeat(3,minmax(0,1fr)); }
}
@media(max-width:600px) {
    .shell { width:min(calc(100% - 28px),var(--shell)); }
    .mark-name { font-size:17px; }
    .mark-name small { font-size:8px; }
    .mark-graphic { width:36px; height:36px; padding:6px; }
    .strip-line { font-size:9px; letter-spacing:.1em; }
    .strip-line span:last-child { display:none; }
    .content { padding-bottom:50px; }
    h1 { font-size:40px; }
    h2 { font-size:28px; }
    p { font-size:16px; }
    .opening { gap:18px; }
    .work-sheet { padding:14px 16px; }
    .sheet-list { grid-template-columns:1fr; gap:0; }
    .sheet-list li { border-bottom:1px solid var(--line-bright); padding:10px 0; }
    .sheet-list li:last-child { border-bottom:0; }
    .section-head { gap:9px; align-items:flex-start; }
    .section-index { margin-top:4px; }
    .chapter { padding:25px 0 29px; }
    .stages { grid-template-columns:1fr; }
    .stages li { border-right:0; border-bottom:1px solid var(--line); padding:15px; }
    .stages li:nth-child(2) { border-bottom:1px solid var(--line); }
    .stages li:last-child { border-bottom:0; }
    .matrix-row { grid-template-columns:1fr; gap:6px; padding:15px; }
    .matrix-row strong { border-left:3px solid var(--warm); padding-left:9px; }
    .matrix-row span { padding-left:12px; }
    .paired { grid-template-columns:1fr; }
    .equations li { grid-template-columns:1fr; gap:5px; padding:14px 15px; }
    .field-notes { grid-template-columns:1fr; }
    .field-notes li:last-child:nth-child(odd) { grid-column:auto; }
    .subject-nav { padding:20px 16px; }
    .subject-nav ul { grid-template-columns:repeat(2,minmax(0,1fr)); gap:0 12px; }
    .footer-row { flex-wrap:wrap; }
    .footer-row>div:nth-child(2) { width:calc(100% - 60px); }
}
@media(max-width:360px) { .subject-nav ul { grid-template-columns:1fr; } .mark-name small { letter-spacing:.03em; } }