:root {
  --ink: #17212b;
  --muted: #586574;
  --line: #cbd3db;
  --soft: #f2f5f7;
  --paper: #fff;
  --navy: #173f68;
  --navy-dark: #102f4f;
  --link: #075ea8;
  --accent: #e6a11f;
  --good: #17643a;
  --max: 1120px;
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--ink);
  background: #e9edf0;
  font-family: Arial, Helvetica, sans-serif;
  font-size: 16px;
  line-height: 1.58;
}
a { color: var(--link); text-decoration-thickness: 1px; text-underline-offset: 2px; }
a:hover { color: #003e70; }
a:focus-visible, button:focus-visible, input:focus-visible, select:focus-visible, textarea:focus-visible, summary:focus-visible {
  outline: 3px solid #f2b84b;
  outline-offset: 2px;
}
.skip-link { position: absolute; left: -9999px; top: 8px; z-index: 20; background: #fff; padding: 8px 12px; }
.skip-link:focus { left: 8px; }
.site-header { background: var(--paper); border-bottom: 1px solid #b9c4ce; }
.header-inner { max-width: var(--max); margin: auto; padding: 18px 20px 14px; display: flex; gap: 28px; align-items: center; }
.brand { color: var(--navy); font-size: 28px; font-weight: 700; text-decoration: none; letter-spacing: -1px; }
.brand span { color: #b86d00; }
.tagline { color: var(--muted); font-size: 14px; }
.main-nav { position: relative; z-index: 10; background: var(--navy); border-bottom: 3px solid #0e3152; }
.nav-inner { max-width: var(--max); margin: auto; padding: 0 20px; }
.main-nav .nav-list { display: flex; align-items: stretch; margin: 0; padding: 0; list-style: none; }
.main-nav .nav-link { position: relative; display: block; min-height: 45px; margin: 0 4px 0 0; border: 0; border-radius: 0; padding: 11px 18px 10px; background: transparent; color: #fff; font: 700 14px Arial, sans-serif; text-decoration: none; }
.main-nav button.nav-link { cursor: pointer; }
.main-nav .nav-link::after { position: absolute; right: 18px; bottom: 0; left: 18px; height: 3px; background: var(--accent); content: ""; opacity: 0; transform: scaleX(.35); transition: opacity .15s ease, transform .15s ease; }
.main-nav .nav-link:hover, .main-nav .nav-link:focus-visible, .main-nav .nav-link[aria-expanded="true"] { background: #204e79; color: #fff; }
.main-nav .nav-link:hover::after, .main-nav .nav-link:focus-visible::after, .main-nav .nav-link[aria-current="page"]::after, .main-nav .section-current::after, .main-nav .nav-link[aria-expanded="true"]::after { opacity: 1; transform: scaleX(1); }
.menu-arrow { display: inline-block; width: 7px; height: 7px; margin: 0 0 3px 9px; border-right: 2px solid currentColor; border-bottom: 2px solid currentColor; transform: rotate(45deg); transition: transform .15s ease; }
.menu-trigger[aria-expanded="true"] .menu-arrow { margin-bottom: -1px; transform: rotate(225deg); }
.mega-menu { position: absolute; top: 100%; right: 0; left: 0; visibility: hidden; border-bottom: 1px solid #8394a3; background: #fff; box-shadow: 0 8px 18px rgba(16, 47, 79, .2); color: var(--ink); opacity: 0; transform: translateY(-5px); transition: opacity .15s ease, transform .15s ease, visibility .15s; }
.menu-trigger[aria-expanded="true"] + .mega-menu { visibility: visible; opacity: 1; transform: translateY(0); }
.mega-inner { display: grid; grid-template-columns: repeat(5, minmax(0, 1fr)); gap: 0; max-width: var(--max); margin: auto; padding: 20px; }
.mega-group { padding: 0 22px; border-left: 1px solid #d4dbe1; }
.mega-group:first-child { padding-left: 0; border-left: 0; }
.mega-group h2 { margin: 0 0 8px; border: 0; padding: 0; color: #435b70; font-size: 12px; letter-spacing: .05em; text-transform: uppercase; }
.main-nav .mega-group ul { display: block; margin: 0; padding: 0; list-style: none; }
.main-nav .mega-group a { display: block; margin: 0 -8px; padding: 5px 8px; color: var(--link); font-size: 14px; font-weight: 700; line-height: 1.35; text-decoration: none; }
.main-nav .mega-group a:hover, .main-nav .mega-group a:focus-visible { background: #edf3f7; color: #003e70; text-decoration: underline; }
.compact-menu .mega-inner { grid-template-columns: 1fr; }
.compact-menu .mega-group { max-width: 280px; border: 0; padding: 0; }
.page-shell { max-width: var(--max); margin: 0 auto; background: #fff; min-height: 65vh; border-left: 1px solid #d2d8de; border-right: 1px solid #d2d8de; }
.content-grid { display: grid; grid-template-columns: minmax(0, 1fr) 290px; gap: 30px; padding: 24px 28px 48px; }
.content-grid > * { min-width: 0; }
.single-column { max-width: 830px; padding: 28px 30px 55px; }
.home-shell { overflow: hidden; }
.home-intro { padding: 42px 44px 34px; background: linear-gradient(90deg, #f7fafc 0, #fff 70%); border-bottom: 1px solid #cbd3db; }
.home-intro h1 { max-width: 760px; font-size: clamp(34px, 5vw, 50px); }
.eyebrow { margin: 0 0 5px; color: #9a5a00; font-size: 12px; font-weight: 700; letter-spacing: .08em; text-transform: uppercase; }
.tool-finder { max-width: 760px; margin-top: 24px; padding: 17px 18px 16px; border: 1px solid #9baab7; border-top: 4px solid var(--navy); background: #fff; box-shadow: 4px 4px 0 #dfe6eb; }
.tool-search-row { display: grid; grid-template-columns: minmax(0, 1fr) auto; gap: 8px; }
.tool-search-row input { margin-top: 6px; padding: 12px 13px; font-size: 17px; }
.tool-search-row button { align-self: end; min-height: 49px; }
.search-help { margin: 7px 0 0; color: var(--muted); font-size: 13px; }
.search-results { margin-top: 10px; }
.search-results:empty { display: none; }
.search-results p { margin: 0 0 5px; color: var(--muted); font-size: 13px; }
.search-results ul { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 4px 20px; margin: 0; padding: 10px 0 0 20px; border-top: 1px solid var(--line); }
.quick-start, .browse-board { padding: 30px 44px; }
.browse-board { background: var(--soft); border-top: 1px solid #d6dde3; border-bottom: 1px solid #d6dde3; }
.section-heading { display: flex; justify-content: space-between; gap: 24px; align-items: end; margin-bottom: 18px; }
.section-heading h2 { margin: 0; border: 0; padding: 0; }
.section-heading > p { max-width: 360px; margin: 0; color: var(--muted); font-size: 14px; text-align: right; }
.featured-grid { display: grid; grid-template-columns: repeat(4, minmax(0, 1fr)); gap: 13px; }
.featured-tool { display: block; min-width: 0; padding: 16px; border: 1px solid #aeb9c3; border-bottom: 3px solid var(--navy); background: #fbfcfd; color: var(--ink); text-decoration: none; transition: transform .15s ease, box-shadow .15s ease; }
.featured-tool:hover, .featured-tool:focus-visible { color: var(--ink); box-shadow: 3px 4px 0 #d6dfe6; transform: translateY(-2px); }
.featured-tool strong { display: block; margin: 8px 0 5px; color: var(--link); font-size: 18px; line-height: 1.25; text-decoration: underline; text-decoration-thickness: 1px; text-underline-offset: 2px; }
.featured-tool > span:last-child { display: block; color: #43515f; font-size: 14px; line-height: 1.45; }
.shelf-grid { display: grid; grid-template-columns: repeat(4, minmax(0, 1fr)); border: 1px solid #aeb9c3; background: #fff; }
.tool-shelf { min-width: 0; padding: 20px 22px; border-left: 1px solid #cbd3db; }
.tool-shelf:first-child { border-left: 0; }
.tool-shelf h3 { margin-top: 0; color: var(--navy); font-size: 20px; }
.tool-shelf p { color: var(--muted); font-size: 14px; }
.tool-shelf ul { padding-left: 20px; }
.tool-shelf li { margin: 7px 0; }
.text-button { border: 0; border-radius: 0; background: transparent; color: var(--link); padding: 2px 0; font-size: 14px; text-decoration: underline; }
.text-button:hover { background: transparent; color: #003e70; }
.site-promise { display: grid; grid-template-columns: minmax(0, 1.3fr) minmax(260px, .7fr); gap: 40px; padding: 34px 44px; }
.site-promise h2 { margin: 0 0 10px; border: 0; padding: 0; }
.site-promise dl { margin: 0; border: 1px solid #b7c1ca; }
.site-promise dl div { display: grid; grid-template-columns: 100px 1fr; gap: 10px; padding: 10px 13px; border-top: 1px solid #d1d8de; }
.site-promise dl div:first-child { border-top: 0; }
.site-promise dt { color: var(--navy); font-weight: 700; }
.site-promise dd { margin: 0; color: var(--muted); }
.home-ad { margin: 0 44px 38px; min-height: 76px; }
.breadcrumbs { color: var(--muted); font-size: 13px; margin-bottom: 14px; }
.breadcrumbs a { color: #475b6d; }
h1, h2, h3 { color: #162d43; line-height: 1.25; }
h1 { margin: 0 0 10px; font-size: clamp(29px, 4vw, 42px); letter-spacing: -0.7px; }
h2 { margin: 38px 0 12px; padding-bottom: 7px; border-bottom: 1px solid var(--line); font-size: 25px; }
h3 { margin: 26px 0 8px; font-size: 19px; }
p { margin: 0 0 16px; }
.lede { color: #3c4d5c; font-size: 18px; max-width: 760px; }
.updated { color: var(--muted); font-size: 13px; margin: 8px 0 20px; }
.quick-answer { border: 2px solid var(--navy); background: #f7fafc; margin: 22px 0; padding: 18px 20px; }
.quick-answer .label { display: block; color: var(--navy); font-size: 13px; font-weight: 700; text-transform: uppercase; letter-spacing: .05em; }
.formula { overflow-x: auto; padding: 8px 0; font-family: Georgia, "Times New Roman", serif; font-size: clamp(22px, 3.5vw, 31px); font-weight: 700; white-space: nowrap; }
.formula-wrap { overflow-wrap: anywhere; white-space: normal; }
.compact-formula { font-family: Georgia, "Times New Roman", serif; font-size: 20px; }
.ad-slot { min-height: 100px; border: 1px dashed #9ca8b2; background: #f7f7f5; color: #6f7880; display: grid; place-content: center; text-align: center; margin: 22px 0; padding: 10px; font-size: 12px; }
.ad-slot span { display: block; font-size: 10px; letter-spacing: .08em; text-transform: uppercase; }
.calculator { border: 1px solid #aeb9c3; background: #f5f7f8; padding: 20px; margin: 18px 0 24px; }
.calculator h2 { margin-top: 0; border: 0; padding: 0; }
.calculator-intro { max-width: 720px; }
.coefficient-grid { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 12px; margin: 16px 0; }
.coefficient-grid label { min-width: 0; }
.polynomial-preview { overflow-x: auto; border: 1px solid #c3ccd4; background: #fff; padding: 12px 14px; margin: 14px 0; font-family: Georgia, "Times New Roman", serif; font-size: 20px; white-space: nowrap; }
.root-list { margin: 10px 0 16px; padding-left: 24px; }
.root-list li { margin: 5px 0; font-family: Georgia, "Times New Roman", serif; font-size: 18px; }
.residual-table td:last-child { font-variant-numeric: tabular-nums; }
.field-row { display: grid; grid-template-columns: 1fr 120px 1fr; gap: 14px; align-items: end; }
.field-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 14px; }
label { display: block; font-weight: 700; font-size: 14px; }
input, select, textarea { width: 100%; margin-top: 5px; padding: 10px 11px; border: 1px solid #7f8b95; border-radius: 2px; background: #fff; color: #111; font: inherit; }
textarea { resize: vertical; line-height: 1.45; }
input[type="checkbox"] { width: auto; margin: 0 6px 0 0; padding: 0; }
.operator-label { text-align: center; }
.button-row { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 16px; }
button, .button-link { border: 1px solid #0c3151; border-radius: 2px; background: var(--navy); color: white; padding: 10px 15px; font: 700 15px Arial, sans-serif; cursor: pointer; text-decoration: none; }
button:hover, .button-link:hover { background: var(--navy-dark); color: #fff; }
button.secondary { color: var(--navy); background: #fff; }
.result { margin-top: 18px; border-left: 4px solid var(--good); background: #fff; padding: 15px 16px; }
.result[hidden] { display: none; }
.result-title { color: var(--good); font-weight: 700; }
.result ol { margin-bottom: 0; padding-left: 22px; }
.result h3 { margin-top: 18px; }
.result-summary { font-size: 19px; color: var(--good); font-weight: 700; }
.result-pair { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 10px; margin: 10px 0 18px; }
.result-pair div { border: 1px solid #b8c4ce; background: #f8fafb; padding: 12px; min-width: 0; }
.result-pair span { display: block; color: var(--muted); font-size: 12px; font-weight: 700; text-transform: uppercase; }
.result-pair strong { display: block; overflow-wrap: anywhere; color: var(--navy); font-size: 21px; }
.number-list { max-height: 280px; overflow: auto; border: 1px solid #c3ccd4; background: #fff; padding: 12px; overflow-wrap: anywhere; }
.live-values { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 10px; margin: 18px 0; }
.live-values div { min-width: 0; border: 1px solid #b8c4ce; background: #f8fafb; padding: 12px; }
.live-values span, .result-pair small { display: block; color: var(--muted); font-size: 12px; }
.live-values strong { display: block; overflow-wrap: anywhere; color: var(--navy); font-size: 20px; font-variant-numeric: tabular-nums; }
.result-pair small { margin-top: 5px; }
.group-row { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr) auto; gap: 12px; align-items: end; margin: 12px 0; padding: 12px; border: 1px solid #b8c4ce; background: #fff; }
.group-row legend { padding: 0 6px; color: var(--navy); font-weight: 700; }
.group-row button { align-self: end; margin-bottom: 0; }
.calculator hr { border: 0; border-top: 1px solid var(--line); margin: 28px 0; }
.table-scroll { max-width: 100%; overflow-x: auto; }
.table-scroll .formula-table { min-width: 650px; }
.compact-calculator { margin-top: 18px; }
.compact-calculator h3 { margin-top: 0; }
.polynomial-coefficients { grid-template-columns: repeat(4, minmax(0, 1fr)); }
.polynomial-steps p { margin-bottom: 7px; }
.matrix-input-wrap { overflow-x: auto; margin: 16px 0; }
.matrix-grid { display: grid; gap: 8px; width: max-content; min-width: 230px; padding: 8px 13px; border-left: 2px solid #30485e; border-right: 2px solid #30485e; }
.matrix-grid.size-2 { grid-template-columns: repeat(2, 86px); }
.matrix-grid.size-3 { grid-template-columns: repeat(3, 76px); }
.matrix-grid input { margin: 0; text-align: center; }
.matrix-display { display: inline-grid; gap: 5px 16px; padding: 8px 13px; margin: 7px 5px; border-left: 2px solid #30485e; border-right: 2px solid #30485e; vertical-align: middle; text-align: right; font-family: Georgia, "Times New Roman", serif; }
.matrix-display.columns-2 { grid-template-columns: repeat(2, minmax(45px, auto)); }
.matrix-display.columns-3 { grid-template-columns: repeat(3, minmax(45px, auto)); }
.matrix-display.columns-4 { grid-template-columns: repeat(4, minmax(45px, auto)); }
.equation-line { overflow-x: auto; white-space: nowrap; margin: 10px 0; }
.system-inputs { max-width: 100%; overflow-x: auto; margin: 16px 0; padding-bottom: 5px; }
.system-equation-row { display: flex; align-items: center; gap: 8px; width: max-content; min-width: 100%; margin: 9px 0; }
.system-coefficient { display: flex; align-items: center; gap: 5px; font-family: Georgia, "Times New Roman", serif; font-size: 18px; }
.system-coefficient input, .system-constant { width: 74px; margin: 0; text-align: center; font-family: Arial, Helvetica, sans-serif; }
.system-constant { display: inline-block; }
.code-block { max-width: 100%; overflow-x: auto; margin: 16px 0; padding: 14px 16px; border: 1px solid #aeb9c3; background: #f4f6f8; color: #17212b; font: 15px/1.55 Consolas, "Courier New", monospace; }
.code-block code { font: inherit; }
.code-inline { overflow-wrap: anywhere; word-break: break-word; }
.verification { border: 1px solid #a9c8b5; background: #f2faf5; padding: 11px 13px; }
.warning-result { border-color: #aa3a2e; background: #fff5f3; }
.pay-breakdown { width: 100%; border-collapse: collapse; margin-top: 14px; }
.pay-breakdown th, .pay-breakdown td { padding: 9px 10px; border-bottom: 1px solid #cbd3db; text-align: left; }
.pay-breakdown td:last-child { text-align: right; font-variant-numeric: tabular-nums; }
.pay-total th, .pay-total td { border-top: 2px solid #647585; font-weight: 700; }
.money-highlight { display: grid; grid-template-columns: repeat(3, 1fr); gap: 10px; margin: 14px 0; }
.money-highlight div { border: 1px solid #b8c4ce; background: #f8fafb; padding: 12px; }
.money-highlight span { display: block; color: var(--muted); font-size: 12px; text-transform: uppercase; }
.money-highlight strong { display: block; color: var(--navy); font-size: 20px; }
.source-list { font-size: 14px; }
.note { background: #fff8e8; border-left: 4px solid var(--accent); padding: 12px 15px; margin: 18px 0; }
.mistake { border-left-color: #aa3a2e; background: #fff5f3; }
.formula-table { width: 100%; border-collapse: collapse; margin: 16px 0; }
.formula-table th, .formula-table td { border: 1px solid #bfc8d0; padding: 10px; text-align: left; vertical-align: top; }
.formula-table th { background: #e8edf1; }
.proof-figure { margin: 20px 0; border: 1px solid #c0c9d1; padding: 14px; background: #fbfcfd; }
.proof-figure img { display: block; width: 100%; max-width: 650px; height: auto; margin: auto; }
.proof-figure figcaption { color: var(--muted); font-size: 13px; margin-top: 10px; }
.toc, .sidebar-box { border: 1px solid #c2cad2; background: #f8fafb; padding: 15px 17px; }
.toc { margin: 20px 0; }
.toc strong, .sidebar-box h2 { display: block; margin: 0 0 8px; border: 0; padding: 0; font-size: 16px; }
.toc ul, .sidebar-box ul { margin: 0; padding-left: 20px; }
.sidebar { padding-top: 18px; }
.sidebar-box { margin-bottom: 18px; }
.sidebar .ad-slot { min-height: 250px; }
.example { border-top: 1px solid #d5dbe0; padding-top: 15px; margin-top: 18px; }
details { border: 1px solid #c5cdd5; border-bottom: 0; padding: 0; }
details:last-of-type { border-bottom: 1px solid #c5cdd5; }
summary { cursor: pointer; font-weight: 700; padding: 13px 15px; background: #f5f7f8; }
details p { padding: 12px 15px 2px; }
.category-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 18px; margin: 24px 0; }
.category-card { border: 1px solid #bcc6cf; padding: 18px; background: #fbfcfd; }
.category-card h2 { border: 0; margin: 0 0 7px; padding: 0; font-size: 20px; }
.badge { display: inline-block; padding: 2px 7px; background: #e8eef3; color: #3e566a; font-size: 12px; font-weight: 700; }
.site-footer { background: #1e2d3a; color: #dce2e7; }
.footer-inner { max-width: var(--max); margin: auto; padding: 28px 20px; display: grid; grid-template-columns: 1fr auto; gap: 25px; }
.footer-links { display: flex; flex-wrap: wrap; gap: 12px 18px; }
.footer-links a { color: #fff; }
.footer-brand { color: #fff; }
.copyright { color: #b9c5ce; font-size: 13px; margin-top: 10px; }
.print-only { display: none; }
@media (max-width: 820px) {
  .header-inner { display: block; }
  .tagline { margin-top: 2px; }
  .content-grid { grid-template-columns: 1fr; padding: 20px 18px 40px; }
  .sidebar { padding-top: 0; }
  .sidebar .ad-slot { min-height: 100px; }
  .category-grid { grid-template-columns: 1fr; }
  .featured-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .shelf-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .tool-shelf { border-top: 1px solid #cbd3db; border-left: 0; }
  .tool-shelf:first-child { border-top: 0; }
  .site-promise { grid-template-columns: 1fr; }
}
@media (max-width: 560px) {
  .nav-inner { padding: 0; }
  .main-nav .nav-list { display: grid; grid-template-columns: repeat(4, auto); overflow-x: auto; }
  .main-nav .nav-link { min-height: 44px; margin: 0; padding: 11px 12px 9px; white-space: nowrap; }
  .main-nav .nav-link::after { right: 12px; left: 12px; }
  .menu-arrow { margin-left: 6px; }
  .mega-menu { position: fixed; top: auto; max-height: calc(100vh - 132px); overflow-y: auto; }
  .mega-inner { grid-template-columns: 1fr; padding: 15px 18px; }
  .mega-group, .mega-group:first-child { padding: 12px 0; border: 0; border-top: 1px solid #d4dbe1; }
  .mega-group:first-child { border-top: 0; }
  .home-intro, .quick-start, .browse-board, .site-promise { padding-right: 20px; padding-left: 20px; }
  .tool-search-row, .featured-grid, .search-results ul { grid-template-columns: 1fr; }
  .tool-search-row button { justify-self: start; min-height: 40px; }
  .section-heading { display: block; }
  .section-heading > p { margin-top: 5px; text-align: left; }
  .home-ad { margin-right: 20px; margin-left: 20px; }
  .field-row { grid-template-columns: 1fr; }
  .operator-label { text-align: left; }
  .footer-inner { grid-template-columns: 1fr; }
  .formula-table { display: block; max-width: 100%; overflow-x: auto; font-size: 14px; }
  .field-grid, .money-highlight, .coefficient-grid, .result-pair, .live-values, .group-row, .shelf-grid { grid-template-columns: 1fr; }
}
@media print {
  body { background: #fff; font-size: 12pt; }
  .site-header, .main-nav, .sidebar, .ad-slot, .calculator, .site-footer, .breadcrumbs, .toc { display: none !important; }
  .page-shell, .content-grid { border: 0; display: block; max-width: none; padding: 0; }
  .print-only { display: block; }
  a { color: #000; text-decoration: none; }
}