:root {
  --navy: #0b2540; --navy-2: #133a5e; --ink: #1a2433; --muted: #5b6878;
  --line: #e2e8f0; --bg: #f7f9fc; --card: #fff; --accent: #ff7a1a; --accent-2: #e5620a;
  --cool: #0e8fd6; --ok: #0f9d6b; --radius: 14px; --shadow: 0 1px 2px rgb(11 37 64 / .06), 0 8px 24px rgb(11 37 64 / .06);
  --font: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
}
*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 80px; }
body { margin: 0; font: 17px/1.65 var(--font); color: var(--ink); background: var(--bg); -webkit-font-smoothing: antialiased; }
img, svg { max-width: 100%; }
a { color: var(--cool); text-underline-offset: 3px; }
a:hover { color: var(--navy-2); }
:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; border-radius: 4px; }
.wrap { width: min(1180px, 100% - 2.5rem); margin-inline: auto; }
.narrow { max-width: 760px; padding-block: 2rem 4rem; }
.skip { position: absolute; left: -999px; }
.skip:focus { left: 1rem; top: 1rem; z-index: 99; background: #fff; padding: .5rem 1rem; }
h1, h2, h3 { line-height: 1.2; color: var(--navy); letter-spacing: -.015em; }
h1 { font-size: clamp(2rem, 4vw, 2.8rem); margin: .3em 0 .4em; }
h2 { font-size: clamp(1.4rem, 2.4vw, 1.75rem); margin: 2.2em 0 .6em; }
h3 { font-size: 1.15rem; margin: 1.6em 0 .4em; }

/* header */
.site-header { position: sticky; top: 0; z-index: 50; background: rgb(11 37 64 / .97); backdrop-filter: blur(8px); color: #fff; }
.bar { display: flex; align-items: center; justify-content: space-between; height: 64px; gap: 1rem; }
.logo { display: flex; align-items: center; gap: .6rem; color: #fff; text-decoration: none; font-weight: 750; font-size: 1.1rem; }
.logo svg { width: 32px; height: 32px; }
.nav { display: flex; align-items: center; gap: .25rem; }
.nav > a, .more summary { color: #d6e2f0; text-decoration: none; padding: .5rem .8rem; border-radius: 8px; font-size: .95rem; cursor: pointer; }
.nav > a:hover, .more summary:hover { background: var(--navy-2); color: #fff; }
.more { position: relative; }
.more summary { list-style: none; }
.more summary::after { content: " ▾"; }
.more .menu, .mobile .menu { position: absolute; right: 0; top: 110%; background: #fff; border-radius: 12px; box-shadow: var(--shadow); padding: .5rem; min-width: 240px; display: grid; }
.menu a { color: var(--ink); text-decoration: none; padding: .55rem .8rem; border-radius: 8px; }
.menu a:hover { background: var(--bg); }
.mobile { display: none; position: relative; }
.mobile summary { list-style: none; cursor: pointer; padding: .45rem .9rem; border: 1px solid #3b5878; border-radius: 8px; }
@media (max-width: 900px) { .nav { display: none; } .mobile { display: block; } }

/* buttons */
.btn { display: inline-block; background: var(--accent); color: #fff; padding: .8rem 1.4rem; border-radius: 10px; text-decoration: none; font-weight: 650; border: 2px solid var(--accent); transition: background .15s; }
.btn:hover { background: var(--accent-2); color: #fff; }
.btn.ghost { background: transparent; border-color: #ffffff55; }
.btn.ghost:hover { background: #ffffff14; }

/* home */
.hero { background: radial-gradient(1000px 400px at 80% -10%, #1f5a8c 0%, transparent 60%), linear-gradient(160deg, var(--navy), #082035); color: #e7eef7; padding: clamp(3rem, 8vw, 6rem) 0; }
.hero h1 { color: #fff; max-width: 17ch; font-size: clamp(2.2rem, 5vw, 3.6rem); }
.hero .lead { max-width: 60ch; font-size: 1.15rem; color: #c4d3e4; }
.cta { display: flex; gap: .8rem; flex-wrap: wrap; margin: 1.8rem 0; }
.stats { display: flex; gap: 2rem; list-style: none; padding: 0; margin: 2rem 0 0; color: #9fb3c9; flex-wrap: wrap; }
.stats strong { display: block; font-size: 1.8rem; color: #fff; }
.eyebrow { text-transform: uppercase; letter-spacing: .08em; font-size: .78rem; font-weight: 700; color: var(--accent); margin: 0; }
.grid3 { display: grid; grid-template-columns: repeat(auto-fit, minmax(260px, 1fr)); gap: 1.5rem; }
.how { padding-bottom: 4rem; }
.how .grid3 > div { background: var(--card); padding: 1.5rem; border-radius: var(--radius); box-shadow: var(--shadow); }
.how h3 { margin-top: 0; }

/* cards */
.cards { display: grid; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); gap: 1rem; }
.card { display: flex; flex-direction: column; gap: .35rem; background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 1.15rem 1.25rem; text-decoration: none; color: var(--ink); transition: transform .15s, box-shadow .15s, border-color .15s; }
.card:hover { transform: translateY(-2px); box-shadow: var(--shadow); border-color: #c8d6e6; color: var(--ink); }
.card strong { color: var(--navy); line-height: 1.3; }
.card span { font-size: .9rem; color: var(--muted); }
.card em { font-style: normal; font-size: .8rem; color: var(--accent-2); font-weight: 650; margin-top: auto; }
.hub { padding-block: 1.5rem 4rem; }
.lead { font-size: 1.12rem; color: var(--muted); max-width: 70ch; }
.related { padding-bottom: 4rem; }

/* article */
.article-grid { display: grid; grid-template-columns: minmax(0, 1fr) 270px; gap: 3rem; padding-block: 1.5rem 3rem; }
@media (max-width: 1000px) { .article-grid { grid-template-columns: 1fr; } .toc { display: none; } }
.crumbs { font-size: .88rem; color: var(--muted); }
.crumbs a { color: var(--muted); }
.prose { max-width: 780px; }
.prose p, .prose li { color: #2a3646; }
.prose ul, .prose ol { padding-left: 1.3rem; }
.prose li { margin: .3rem 0; }
.prose table { width: 100%; border-collapse: collapse; margin: 1.2rem 0; font-size: .95rem; background: var(--card); border-radius: 10px; overflow: hidden; box-shadow: 0 0 0 1px var(--line); display: block; overflow-x: auto; }
.prose th, .prose td { padding: .6rem .8rem; text-align: left; border-bottom: 1px solid var(--line); white-space: nowrap; }
.prose th { background: #eef3f9; color: var(--navy); font-weight: 650; }
.prose tr:last-child td { border-bottom: 0; }
.prose blockquote, .callout { margin: 1.4rem 0; padding: 1rem 1.2rem; border-left: 4px solid var(--cool); background: #eaf5fc; border-radius: 0 10px 10px 0; }
.callout.warn { border-color: var(--accent); background: #fff3ea; }
.formula { font-family: ui-monospace, SFMono-Regular, Consolas, monospace; background: var(--navy); color: #e7eef7; padding: 1rem 1.2rem; border-radius: 10px; overflow-x: auto; font-size: .95rem; }
.tldr { background: var(--card); border: 1px solid var(--line); border-left: 4px solid var(--ok); border-radius: 0 var(--radius) var(--radius) 0; padding: 1rem 1.3rem; margin: 1rem 0 1.5rem; }
.tldr strong { color: var(--ok); font-size: .82rem; text-transform: uppercase; letter-spacing: .07em; }
.tldr p { margin: .3rem 0 0; }
.toc .sticky { position: sticky; top: 88px; background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 1.1rem 1.2rem; font-size: .9rem; max-height: calc(100vh - 110px); overflow: auto; }
.toc h2 { font-size: .8rem; text-transform: uppercase; letter-spacing: .08em; margin: 0 0 .6rem; color: var(--muted); }
.toc ol { margin: 0 0 1rem; padding-left: 1.1rem; }
.toc li { margin: .35rem 0; }
.toc a { color: var(--ink); text-decoration: none; }
.toc a:hover { color: var(--cool); }
.toc .btn { display: block; text-align: center; padding: .6rem; font-size: .9rem; }
details { background: var(--card); border: 1px solid var(--line); border-radius: 10px; margin: .6rem 0; }
details summary { cursor: pointer; padding: .9rem 1.1rem; font-weight: 600; color: var(--navy); }
details > div { padding: 0 1.1rem 1rem; }
.site-header details { background: none; border: 0; margin: 0; }
.site-header details summary { font-weight: 400; color: #d6e2f0; }
.updated { font-size: .85rem; color: var(--muted); margin-top: 3rem; }

/* calculator */
.calc { background: var(--card); border: 1px solid var(--line); border-radius: 18px; box-shadow: var(--shadow); padding: clamp(1.2rem, 3vw, 2rem); margin: 1.5rem 0 2rem; }
.calc h2 { margin-top: 0; }
.fields { display: grid; grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); gap: 1rem 1.2rem; }
.fields label { display: flex; flex-direction: column; gap: .35rem; font-weight: 600; font-size: .92rem; color: var(--navy); }
.fields small { font-weight: 400; color: var(--muted); }
.ctl { display: flex; align-items: center; border: 1.5px solid #cfd9e5; border-radius: 10px; background: #fff; overflow: hidden; }
.ctl:focus-within { border-color: var(--cool); box-shadow: 0 0 0 3px #0e8fd622; }
.ctl input, .ctl select { flex: 1; min-width: 0; border: 0; padding: .7rem .8rem; font: inherit; font-weight: 400; color: var(--ink); background: transparent; outline: none; }
.unit { padding: 0 .8rem; color: var(--muted); font-weight: 500; font-size: .85rem; background: #f2f6fa; align-self: stretch; display: flex; align-items: center; }
.calc button { margin-top: 1.3rem; background: var(--navy); color: #fff; border: 0; padding: .8rem 1.6rem; border-radius: 10px; font: inherit; font-weight: 650; cursor: pointer; }
.calc button:hover { background: var(--navy-2); }
.results { display: grid; grid-template-columns: repeat(auto-fit, minmax(190px, 1fr)); gap: .8rem; margin-top: 1.4rem; }
.result { background: var(--bg); border-radius: 12px; padding: .9rem 1rem; display: flex; flex-direction: column; }
.result span { font-size: .82rem; color: var(--muted); }
.result strong { font-size: 1.35rem; color: var(--navy); }
.result.primary { background: linear-gradient(135deg, var(--navy), var(--navy-2)); }
.result.primary span { color: #a9bfd6; }
.result.primary strong { color: #fff; font-size: 1.7rem; }
.result small { font-size: .8rem; font-weight: 500; opacity: .8; }
.error { color: #c0392b; }

/* footer */
.site-footer { background: var(--navy); color: #a9bfd6; padding: 3.5rem 0 1.5rem; font-size: .93rem; }
.grid4 { display: grid; grid-template-columns: 1.5fr repeat(3, 1fr); gap: 2rem; }
@media (max-width: 800px) { .grid4 { grid-template-columns: 1fr 1fr; } }
.site-footer h2 { color: #fff; font-size: .85rem; text-transform: uppercase; letter-spacing: .08em; margin: 0 0 .8rem; }
.site-footer ul { list-style: none; padding: 0; margin: 0; }
.site-footer li { margin: .35rem 0; }
.site-footer a { color: #d6e2f0; text-decoration: none; }
.site-footer a:hover { color: #fff; text-decoration: underline; }
.logo-text { color: #fff; font-weight: 750; font-size: 1.1rem; margin: 0 0 .5rem; }
.fine { border-top: 1px solid #ffffff1a; margin-top: 2.5rem; padding-top: 1.2rem; font-size: .82rem; }
@media (prefers-reduced-motion: reduce) { * { transition: none !important; scroll-behavior: auto !important; } }
@media print { .site-header, .site-footer, .toc, .related, .calc button { display: none; } }

/* homepage explainers (inline SVG) */
.explainers { padding-top: 1rem; }
.explainer { margin: 0; background: var(--card); border: 1px solid var(--line); border-radius: 18px; box-shadow: var(--shadow); overflow: hidden; display: flex; flex-direction: column; }
.explainer svg { display: block; width: 100%; height: auto; background: #fbfdff; border-bottom: 1px solid var(--line); padding: .75rem; }
.explainer figcaption { padding: 1.1rem 1.3rem 1.3rem; display: flex; flex-direction: column; gap: .2rem; flex: 1; }
.explainer h3 { margin: 0 0 .2rem; }
.explainer p { margin: 0 0 .6rem; color: #2a3646; font-size: .97rem; }
.explainer a { margin-top: auto; font-weight: 650; text-decoration: none; }
.explainer.wide { display: grid; grid-template-columns: minmax(0, 1.6fr) minmax(0, 1fr); margin-bottom: 1.2rem; }
.explainer.wide svg { border-bottom: 0; border-right: 1px solid var(--line); padding: 0; }
.explainer.wide figcaption { justify-content: center; padding: 1.5rem 1.8rem; }
.explainer-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); gap: 1.2rem; }
@media (max-width: 860px) { .explainer.wide { grid-template-columns: 1fr; } .explainer.wide svg { border-right: 0; border-bottom: 1px solid var(--line); } }
.calc-group { padding-top: .5rem; }
.calc-group h2 { margin-bottom: .2rem; }
.calc-group .lead { margin: 0 0 1rem; font-size: 1rem; }
.nav > a[aria-current="page"] { background: var(--navy-2); color: #fff; box-shadow: inset 0 -2px 0 var(--accent); }
.menu a[aria-current="page"] { font-weight: 700; color: var(--accent-2); }