:root {
  --bg: #f5f6f8;
  --surface: #ffffff;
  --surface-2: #eef1f5;
  --fg: #14181f;
  --muted: #5a626e;
  --border: #dde1e7;
  --field-border: #848c99;
  --accent: #1f5ea8;
  --accent-fg: #ffffff;
  --accent-soft: #e6eef8;
  --good: #1d7a46;
  --bad: #b3261e;
  --warn-bg: #fff4e5;
  --warn-fg: #8a4b00;
  --chart-grid: #e6e9ee;
  --sketch-fill: #dfe6ef;
  --sketch-fill-2: #c3d0e0;
  --radius: 8px;
  --mono: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0f1216; --surface: #171b21; --surface-2: #1f252d; --fg: #e7eaef; --muted: #9aa3af;
    --border: #2b323c; --field-border: #6b7482; --accent: #6aa5ec; --accent-fg: #0b1018; --accent-soft: #1b2a3d;
    --good: #5cc98c; --bad: #ff8a80; --warn-bg: #2e2312; --warn-fg: #f3c27a; --chart-grid: #262c35; --sketch-fill: #2a3542; --sketch-fill-2: #3d4b5c;
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #0f1216; --surface: #171b21; --surface-2: #1f252d; --fg: #e7eaef; --muted: #9aa3af;
  --border: #2b323c; --field-border: #6b7482; --accent: #6aa5ec; --accent-fg: #0b1018; --accent-soft: #1b2a3d;
  --good: #5cc98c; --bad: #ff8a80; --warn-bg: #2e2312; --warn-fg: #f3c27a; --chart-grid: #262c35; --sketch-fill: #2a3542; --sketch-fill-2: #3d4b5c;
  color-scheme: dark;
}

* { box-sizing: border-box; }
html, body { margin: 0; }
body {
  background: var(--bg); color: var(--fg);
  font: 14px/1.45 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
}
a { color: var(--accent); }
button, input, select, textarea { font: inherit; color: inherit; }
/* Keyboard focus: one clearly visible ring everywhere (WCAG 2.4.7). */
:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
main:focus { outline: none; }
.skip-link {
  position: absolute; left: 8px; top: -100px; z-index: 100;
  background: var(--accent); color: var(--accent-fg); padding: 8px 12px; border-radius: 6px; font-weight: 600;
}
.skip-link:focus { top: 8px; }

/* Header */
.topbar {
  position: sticky; top: 0; z-index: 10;
  display: flex; align-items: center; gap: 12px;
  padding: 10px 16px; background: var(--surface); border-bottom: 1px solid var(--border);
}
.topbar h1 { font-size: 16px; margin: 0; font-weight: 650; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; min-width: 0; }
.topbar h1 small { font-weight: 400; color: var(--muted); margin-left: 6px; }
.topbar .spacer { flex: 1; }
.topbar .toolbar { flex-wrap: nowrap; }

.btn {
  display: inline-flex; align-items: center; gap: 6px;
  border: 1px solid var(--border); background: var(--surface); color: var(--fg);
  padding: 6px 11px; border-radius: 6px; cursor: pointer; white-space: nowrap;
}
.btn:hover { background: var(--surface-2); }
.btn.primary { background: var(--accent); border-color: var(--accent); color: var(--accent-fg); }
.btn.primary:hover { filter: brightness(1.08); }
.btn.small { padding: 3px 8px; font-size: 13px; }
.btn.danger { color: var(--bad); }
.toolbar { display: flex; flex-wrap: wrap; gap: 6px; }
select.btn.lang-select { padding-right: 6px; appearance: auto; }
/* Segmented switch (unit system) */
.seg { display: inline-flex; border: 1px solid var(--border); border-radius: 6px; overflow: hidden; }
.seg button { font: inherit; font-size: 13px; color: inherit; background: var(--surface); border: 0; padding: 6px 10px; cursor: pointer; white-space: nowrap; }
.seg button + button { border-left: 1px solid var(--border); }
.seg button:hover { background: var(--surface-2); }
.seg button[aria-pressed="true"] { background: var(--accent); color: var(--accent-fg); }
.seg button:focus-visible { outline: 2px solid var(--accent); outline-offset: -2px; }
.seg .short { display: none; }

/* Layout */
.layout { display: grid; grid-template-columns: 260px 1fr; min-height: calc(100vh - 53px); }
.sidebar {
  background: var(--surface); border-right: 1px solid var(--border);
  padding: 12px; position: sticky; top: 53px; height: calc(100vh - 53px); overflow-y: auto;
}
/* Desktop: the menu button hides/shows the calculator list to give the page full width. */
body.nav-collapsed .layout { grid-template-columns: 1fr; }
body.nav-collapsed .sidebar { display: none; }
.sidebar input[type="search"] {
  width: 100%; padding: 7px 10px; border: 1px solid var(--field-border); border-radius: 6px; background: var(--bg);
}
.nav-group { margin-top: 14px; }
.nav-group h2 { font-size: 11px; text-transform: uppercase; letter-spacing: .06em; color: var(--muted); margin: 0 0 4px 6px; }
.nav-item {
  display: block; width: 100%; text-align: left; border: 0; background: none; cursor: pointer;
  padding: 6px 8px; border-radius: 6px; color: var(--fg);
}
.nav-item:hover { background: var(--surface-2); }
.nav-item.active { background: var(--accent-soft); color: var(--accent); font-weight: 600; }

main { padding: 20px 24px 48px; max-width: 1280px; min-width: 0; }
.calc-head h2 { margin: 0 0 4px; font-size: 22px; }
.calc-head p { margin: 0 0 6px; color: var(--muted); max-width: 75ch; }
.calc-head .meta { font-size: 13px; color: var(--muted); }
.calc-head .loaded { color: var(--accent); font-weight: 600; }
.calc-actions { margin: 14px 0 18px; }

.grid { display: grid; grid-template-columns: minmax(300px, 420px) 1fr; gap: 18px; align-items: start; }
.card { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 14px 16px; min-width: 0; }
.card h3 { margin: 0 0 8px; font-size: 14px; }

/* Form */
.form-section { font-size: 12px; text-transform: uppercase; letter-spacing: .05em; color: var(--muted); margin: 14px 0 6px; font-weight: 600; }
.form-section:first-child { margin-top: 0; }
.field { display: grid; grid-template-columns: 1fr 120px 64px; gap: 8px; align-items: center; padding: 3px 0; }
.field label { font-size: 13px; }
.field label .sym { color: var(--muted); margin-left: 4px; font-style: italic; }
.field .hint { grid-column: 1 / -1; font-size: 12px; color: var(--muted); margin-top: -2px; }
.field input, .field select {
  width: 100%; padding: 5px 8px; border: 1px solid var(--field-border); border-radius: 5px; background: var(--bg);
}
.field input { text-align: right; font-variant-numeric: tabular-nums; }
.field.wide { grid-template-columns: 1fr 184px; }
.field .unit { font-size: 12px; color: var(--muted); }
.field input.invalid { border-color: var(--bad); background: color-mix(in srgb, var(--bad) 8%, var(--bg)); }
.field input:focus, .field select:focus, .project input:focus, .project textarea:focus { outline: 2px solid var(--accent); outline-offset: -1px; }
.project { display: grid; gap: 6px; margin-top: 16px; }
.project input, .project textarea { width: 100%; padding: 6px 8px; border: 1px solid var(--field-border); border-radius: 5px; background: var(--bg); }
.project textarea { min-height: 56px; resize: vertical; }

/* Results */
table.results { width: 100%; border-collapse: collapse; font-variant-numeric: tabular-nums; }
table.results td { padding: 5px 6px; border-bottom: 1px solid var(--border); vertical-align: top; }
table.results td.sym { color: var(--muted); font-style: italic; white-space: nowrap; }
table.results td.val { text-align: right; font-weight: 600; font-family: var(--mono); font-size: 13px; white-space: nowrap; }
table.results td.unit { color: var(--muted); white-space: nowrap; width: 1%; }
table.results tr.section td { border-bottom: 0; padding-top: 12px; font-size: 12px; text-transform: uppercase; letter-spacing: .05em; color: var(--accent); font-weight: 600; }
table.results tr.good td.val { color: var(--good); }
table.results tr.bad td.val { color: var(--bad); }
.warnings { margin: 0 0 12px; padding: 10px 12px; background: var(--warn-bg); color: var(--warn-fg); border-radius: 6px; font-size: 13px; }
.warnings ul { margin: 0; padding-left: 18px; }
.charts canvas { display: block; max-width: 100%; margin-top: 12px; border-radius: 6px; }
.formulas { margin-top: 18px; }
.formulas ul { margin: 0; padding-left: 18px; font-family: var(--mono); font-size: 12.5px; line-height: 1.7; }
.disclaimer { margin-top: 18px; font-size: 12px; color: var(--muted); }
.corrections { margin-top: 18px; }
.corrections ul { margin: 0; padding-left: 18px; font-size: 13.5px; line-height: 1.6; }
.corrections li + li { margin-top: 6px; }
.corrections h4 { margin: 14px 0 6px; font-size: 13px; }
.corrections .cite { color: var(--muted); white-space: nowrap; }
.corrections .refs { margin: 0; padding-left: 22px; font-size: 12px; line-height: 1.55; color: var(--muted); }
.mat-note { font-size: 10px; margin-left: 2px; cursor: help; }

/* Theory help next to the calculator title */
.title-row { display: flex; align-items: center; gap: 10px; margin-bottom: 4px; }
.title-row h2 { margin: 0; }
.help { position: relative; flex: none; }
.help-btn {
  width: 26px; height: 26px; border-radius: 50%; border: 1.5px solid var(--accent); background: var(--accent-soft);
  color: var(--accent); font-weight: 700; font-size: 14px; line-height: 1; cursor: help; padding: 0;
}
.help-btn:hover, .help-btn[aria-expanded="true"] { background: var(--accent); color: var(--accent-fg); }
.help-btn:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.help-pop {
  position: absolute; top: calc(100% + 8px); left: 0; z-index: 20;
  width: min(460px, calc(100vw - 32px)); max-height: min(70vh, 560px); overflow-y: auto;
  background: var(--surface); color: var(--fg); border: 1px solid var(--border); border-radius: var(--radius);
  box-shadow: 0 10px 30px rgb(0 0 0 / .18); padding: 12px 14px; font-size: 13px;
}
.help-pop[hidden] { display: none; }
.help-pop h3 { margin: 0 0 6px; font-size: 14px; }
.help-pop h4 { margin: 10px 0 4px; font-size: 11px; text-transform: uppercase; letter-spacing: .05em; color: var(--muted); }
.help-pop p { margin: 0 0 4px; color: var(--fg); max-width: none; }
.help-pop ul { margin: 0; padding-left: 18px; }
.help-pop li { margin: 2px 0; }
.help-pop .help-tip { margin-top: 10px; color: var(--accent); }
.help-pop .help-src { margin-top: 8px; font-size: 12px; }

/* Geometry preview */
.preview { margin-bottom: 18px; }
.preview-head { display: flex; align-items: center; justify-content: space-between; gap: 8px; margin-bottom: 8px; }
.preview-head h3 { margin: 0; }
.preview-caption { margin: 6px 0 0; font-size: 12.5px; font-family: var(--mono); color: var(--accent); min-height: 1.45em; }
.preview svg { display: block; width: 100%; height: auto; max-height: 360px; }
.preview-notes { margin: 6px 0 0; font-size: 12px; color: var(--muted); }

/* Materials table */
.table-wrap { overflow-x: auto; }
table.materials { border-collapse: collapse; width: 100%; font-variant-numeric: tabular-nums; font-size: 13px; }
table.materials th, table.materials td { padding: 6px 8px; border-bottom: 1px solid var(--border); text-align: right; white-space: nowrap; }
table.materials th:first-child, table.materials td:first-child { text-align: left; }
table.materials th { position: sticky; top: 0; background: var(--surface); font-size: 12px; color: var(--muted); }

/* Dialog */
dialog {
  border: 1px solid var(--border); border-radius: 10px; padding: 0; width: min(680px, calc(100vw - 32px));
  background: var(--surface); color: var(--fg);
}
dialog::backdrop { background: rgb(0 0 0 / .35); }
.dialog-head { display: flex; align-items: center; gap: 10px; padding: 12px 16px; border-bottom: 1px solid var(--border); }
.dialog-head h3 { margin: 0; flex: 1; font-size: 15px; }
.dialog-body { padding: 12px 16px 16px; max-height: 60vh; overflow-y: auto; }
.snap { display: grid; grid-template-columns: 1fr auto; gap: 8px; align-items: center; padding: 8px 0; border-bottom: 1px solid var(--border); }
.snap .name { font-weight: 600; word-break: break-word; }
.snap .info { font-size: 12px; color: var(--muted); }
.snap .acts { display: flex; gap: 6px; }
.empty { color: var(--muted); padding: 12px 0; }

.toast {
  position: fixed; bottom: 20px; left: 50%; transform: translateX(-50%);
  background: var(--fg); color: var(--bg); padding: 8px 14px; border-radius: 6px; font-size: 13px;
  opacity: 0; transition: opacity .2s; pointer-events: none; z-index: 50;
}
.toast.show { opacity: 1; }

@media (max-width: 1000px) {
  .grid { grid-template-columns: 1fr; }
}
@media (max-width: 760px) {
  .layout { grid-template-columns: 1fr; }
  .sidebar { display: none; position: fixed; top: 53px; left: 0; right: 0; bottom: 0; height: auto; z-index: 9; border-right: 0; }
  body.nav-open .sidebar { display: block; }
  body.nav-collapsed .layout { grid-template-columns: 1fr; }
  .topbar h1 small { display: none; }
  .seg button { padding: 6px 8px; }
  .seg .long { display: none; }
  .seg .short { display: inline; }
  .topbar { gap: 8px; padding: 10px 12px; }
  .topbar h1 { font-size: 15px; }
  main { padding: 16px 16px 40px; }
  .help { position: static; }
  .title-row { position: relative; }
  .field { grid-template-columns: 1fr 104px 52px; }
  .field.wide { grid-template-columns: 1fr; }
}

@media print {
  .topbar, .sidebar, .calc-actions, .project, .no-print, .help, #btnAnim, .preview-caption { display: none !important; }
  .layout { display: block; }
  body { background: #fff; color: #000; }
  .card { border: 0; padding: 0; }
  .grid { grid-template-columns: 1fr 1fr; }
}