/* Stair & Roof: charcoal + carpenter-pencil yellow, square corners, blueprint grid in the work area */
[hidden] { display: none !important; }
:root {
  --bg: #f7f6f2; --sheet: #ffffff; --ink: #1f2329; --ink-2: #4b525c; --ink-3: #6c737d; --edge: #d9d6cc; --edge-2: #ebe8df;
  --char: #23272e; --on-char: #f2f0ea; --pencil: #f2b705; --on-pencil: #1f2329; --blue: #1f5fa8; --blue-wash: #eaf1fa;
  --good: #23743f; --bad: #b3261e; --grid: rgba(31, 95, 168, .07);
  --f-head: "Avenir Next", "Futura", "Century Gothic", "Segoe UI", system-ui, sans-serif;
  --f-body: system-ui, -apple-system, "Segoe UI", Roboto, Ubuntu, sans-serif;
}
@media (prefers-color-scheme: dark) { :root {
  --bg: #15181c; --sheet: #1d2126; --ink: #ecebe6; --ink-2: #c4c7cc; --ink-3: #969ba3; --edge: #343a42; --edge-2: #2a2f36;
  --char: #0f1114; --on-char: #ecebe6; --pencil: #f5c534; --on-pencil: #15181c; --blue: #79aef0; --blue-wash: #1c2a3b;
  --good: #6fcf8e; --bad: #ff8a80; --grid: rgba(121, 174, 240, .08); } }
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body { margin: 0; background: var(--bg); color: var(--ink); font: 17px/1.6 var(--f-body); }
a { color: var(--blue); text-decoration-thickness: 1px; text-underline-offset: 2px; }
.wrap { max-width: 1080px; margin: 0 auto; padding: 0 16px; }
.skip { position: absolute; left: -9999px; } .skip:focus { left: 12px; top: 12px; z-index: 9; background: var(--pencil); color: var(--on-pencil); padding: 8px 12px; }

.top { background: var(--char); color: var(--on-char); border-bottom: 4px solid var(--pencil); }
.top-in { display: flex; align-items: center; justify-content: space-between; flex-wrap: wrap; gap: 8px 24px; min-height: 60px; padding-top: 6px; padding-bottom: 6px; }
.logo { display: inline-flex; align-items: center; gap: 10px; color: var(--on-char); text-decoration: none; font: 700 21px/1 var(--f-head); letter-spacing: .02em; text-transform: uppercase; }
.logo i { font-style: normal; color: var(--pencil); margin: 0 2px; }
.mark { width: 30px; height: 30px; color: var(--on-char); }
.menu { display: flex; flex-wrap: wrap; gap: 4px 18px; font: 600 14px var(--f-head); letter-spacing: .04em; text-transform: uppercase; }
.menu a { color: var(--on-char); text-decoration: none; opacity: .82; padding: 4px 0; }
.menu a:hover, .menu a[aria-current] { opacity: 1; box-shadow: inset 0 -2px 0 var(--pencil); }

.trail { margin: 18px 0 0; font-size: 14px; color: var(--ink-3); }
.trail a { color: var(--ink-2); } .trail .sep { margin: 0 8px; color: var(--edge); }
.head { margin: 12px 0 20px; max-width: 760px; }
h1 { font: 700 clamp(28px, 4.2vw, 42px)/1.12 var(--f-head); letter-spacing: -.005em; margin: 0 0 10px; }
h2 { font: 700 clamp(21px, 2.6vw, 27px)/1.25 var(--f-head); margin: 46px 0 12px; }
h3 { font: 700 18px/1.3 var(--f-head); margin: 26px 0 8px; }
.answer { font-size: 19px; color: var(--ink-2); margin: 0; border-left: 4px solid var(--pencil); padding-left: 14px; }
.prose { max-width: 760px; }
.prose p, .prose li { color: var(--ink-2); }
.prose strong { color: var(--ink); }
.num { font-variant-numeric: tabular-nums; }

/* work area: form + result side by side */
.bench { display: grid; grid-template-columns: minmax(0, 340px) minmax(0, 1fr); gap: 0; background: var(--sheet); border: 1px solid var(--edge); }
@media (max-width: 820px) { .bench { grid-template-columns: 1fr; } }
.inputs { padding: 18px; border-right: 1px solid var(--edge); }
@media (max-width: 820px) { .inputs { border-right: 0; border-bottom: 1px solid var(--edge); } }
.out { padding: 18px; background-color: var(--sheet); background-image: linear-gradient(var(--grid) 1px, transparent 1px), linear-gradient(90deg, var(--grid) 1px, transparent 1px); background-size: 20px 20px; min-width: 0; }
.units { display: inline-flex; border: 1px solid var(--edge); margin-bottom: 14px; }
.units button { font: 600 13px var(--f-head); letter-spacing: .04em; text-transform: uppercase; border: 0; background: transparent; color: var(--ink-2); padding: 7px 14px; cursor: pointer; }
.units button[aria-pressed="true"] { background: var(--char); color: var(--on-char); }
.field { margin-bottom: 13px; }
.field label { display: block; font: 600 14px var(--f-head); margin-bottom: 4px; }
.field small { display: block; color: var(--ink-3); font-size: 13px; line-height: 1.4; margin-top: 3px; }
.field input, .field select { width: 100%; font: 17px var(--f-body); padding: 9px 10px; border: 1px solid var(--edge); border-radius: 0; background: var(--bg); color: var(--ink); }
.field input:focus, .field select:focus { outline: 3px solid var(--pencil); outline-offset: 0; border-color: var(--char); }
.field input[aria-invalid="true"] { border-color: var(--bad); }
.pair { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; }
details.more { margin: 4px 0 10px; } details.more summary { cursor: pointer; font: 600 14px var(--f-head); color: var(--blue); padding: 4px 0; }
.go { width: 100%; font: 700 15px var(--f-head); letter-spacing: .05em; text-transform: uppercase; background: var(--pencil); color: var(--on-pencil); border: 0; padding: 12px; cursor: pointer; }
.go:hover { filter: brightness(.95); }

.big { display: grid; grid-template-columns: repeat(auto-fit, minmax(140px, 1fr)); gap: 10px; margin-bottom: 14px; }
.big div { background: var(--sheet); border: 1px solid var(--edge); padding: 10px 12px; }
.big b { display: block; font: 700 22px/1.2 var(--f-head); font-variant-numeric: tabular-nums; }
.big span { font-size: 13px; color: var(--ink-3); }
.big .key { border-color: var(--char); box-shadow: inset 0 4px 0 var(--pencil); }
.drawing { background: var(--sheet); border: 1px solid var(--edge); margin: 0 0 14px; }
.drawing svg { display: block; width: 100%; height: auto; }
.drawing figcaption { font-size: 13px; color: var(--ink-3); padding: 6px 10px; border-top: 1px solid var(--edge-2); }
.code { list-style: none; padding: 0; margin: 0 0 12px; background: var(--sheet); border: 1px solid var(--edge); }
.code li { display: flex; gap: 10px; align-items: baseline; padding: 7px 10px; border-top: 1px solid var(--edge-2); font-size: 15px; }
.code li:first-child { border-top: 0; }
.code .st { font-weight: 700; min-width: 36px; } .code .ok { color: var(--good); } .code .no { color: var(--bad); }
.code em { margin-left: auto; font-style: normal; color: var(--ink-3); font-size: 13px; white-space: nowrap; }
.tools { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 4px; }
.tools button { font: 600 13px var(--f-head); background: var(--sheet); color: var(--ink); border: 1px solid var(--char); padding: 7px 12px; cursor: pointer; }
.hint { color: var(--ink-3); font-size: 15px; }
.warn { background: #fff4d1; color: #4d3a00; border-left: 4px solid var(--pencil); padding: 8px 12px; margin: 0 0 12px; font-size: 15px; }
@media (prefers-color-scheme: dark) { .warn { background: #3a3012; color: #f6e7b3; } }

.scroll { overflow-x: auto; -webkit-overflow-scrolling: touch; margin: 10px 0 6px; border: 1px solid var(--edge); background: var(--sheet); }
table { border-collapse: collapse; width: 100%; font-size: 15px; font-variant-numeric: tabular-nums; }
th, td { text-align: left; padding: 8px 10px; border-top: 1px solid var(--edge-2); white-space: nowrap; }
thead th { background: var(--char); color: var(--on-char); font: 600 13px var(--f-head); letter-spacing: .03em; text-transform: uppercase; border-top: 0; }
tr.pick td { background: var(--blue-wash); font-weight: 700; }
.tag { display: inline-block; font: 700 11px var(--f-head); letter-spacing: .05em; text-transform: uppercase; padding: 1px 6px; border: 1px solid currentColor; }
.tag.ok { color: var(--good); } .tag.no { color: var(--bad); }

.tiles { display: grid; grid-template-columns: repeat(auto-fit, minmax(230px, 1fr)); gap: 12px; margin: 14px 0; }
.tile { display: block; background: var(--sheet); border: 1px solid var(--edge); padding: 14px 16px; color: var(--ink); text-decoration: none; }
a.tile:hover { border-color: var(--char); box-shadow: inset 0 -4px 0 var(--pencil); }
.tile h3 { margin: 0 0 4px; } .tile p { margin: 0; color: var(--ink-3); font-size: 15px; }
.tile.soon { border-style: dashed; } .tile.soon h3::after { content: " · in progress"; font: 600 12px var(--f-head); color: var(--ink-3); text-transform: uppercase; }
.steps { counter-reset: s; list-style: none; padding: 0; }
.steps li { counter-increment: s; position: relative; padding-left: 40px; margin: 10px 0; }
.steps li::before { content: counter(s); position: absolute; left: 0; top: 1px; width: 26px; height: 26px; background: var(--char); color: var(--pencil); font: 700 14px/26px var(--f-head); text-align: center; }
.faq details { border-top: 1px solid var(--edge); padding: 10px 0; } .faq details:last-child { border-bottom: 1px solid var(--edge); }
.faq summary { cursor: pointer; font: 600 17px var(--f-head); }
.faq p { margin: 8px 0 0; color: var(--ink-2); }
.formula { font: 15px/1.6 ui-monospace, Menlo, Consolas, monospace; background: var(--sheet); border: 1px solid var(--edge); border-left: 4px solid var(--blue); padding: 10px 14px; overflow-x: auto; }
.byline { font-size: 14px; color: var(--ink-3); margin: 34px 0 0; border-top: 1px solid var(--edge); padding-top: 12px; }

.foot { margin-top: 64px; background: var(--char); color: var(--on-char); padding: 26px 0 30px; font-size: 15px; }
.foot-in { display: grid; gap: 14px; }
.foot nav { display: flex; flex-wrap: wrap; gap: 6px 18px; } .foot a { color: var(--on-char); }
.foot .fine { margin: 0; opacity: .7; font-size: 13px; }

@media print {
  .top, .foot, .inputs, .tools, .trail, .skip, #dev-panel, #dev-toggle { display: none !important; }
  body { background: #fff; color: #000; } .bench { border: 0; display: block; } .out { background: none; }
}
@media (prefers-reduced-motion: reduce) { * { transition: none !important; animation: none !important; } }