:root {
  --bg: #f4f6f9;
  --card: #ffffff;
  --ink: #1f2933;
  --muted: #5b6b7b;
  --line: #dce3ea;
  --accent: #1f6feb;
  --accent2: #0b3d91;
  --res: #e8f3ff;
  --warn: #fff4e5;
  --eng: #0b7d3e;
}
* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  font-family: "Segoe UI", system-ui, -apple-system, "Helvetica Neue", Arial, "Microsoft YaHei", "Noto Sans CJK", sans-serif;
  background: var(--bg);
  color: var(--ink);
  line-height: 1.55;
  font-size: 15px;
}
a { color: var(--accent); text-decoration: none; }

/* Header */
.app-header {
  background: linear-gradient(90deg, var(--accent2), var(--accent));
  color: #fff;
  padding: 0 18px;
  position: sticky;
  top: 0;
  z-index: 50;
  box-shadow: 0 2px 8px rgba(0,0,0,.12);
}
.app-header .inner {
  max-width: 1180px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  gap: 14px;
  height: 58px;
}
.brand { font-weight: 700; font-size: 18px; letter-spacing: .3px; white-space: nowrap; }
.brand small { font-weight: 400; opacity: .8; font-size: 12px; margin-left: 6px; }
.header-spacer { flex: 1; }
.lang-select {
  background: rgba(255,255,255,.15);
  color: #fff;
  border: 1px solid rgba(255,255,255,.4);
  border-radius: 6px;
  padding: 6px 10px;
  font-size: 13px;
  cursor: pointer;
}
.lang-select option { color: #1f2933; }
.btn-top {
  background: #fff;
  color: var(--accent2);
  border: none;
  border-radius: 6px;
  padding: 7px 14px;
  font-weight: 600;
  font-size: 13px;
  cursor: pointer;
  white-space: nowrap;
}
.btn-top:hover { background: #eef4ff; }
.btn-mail { background: #ffd34d; color: #1f2933; }

/* Layout */
.container { max-width: 1180px; margin: 22px auto; padding: 0 18px; }
.crumbs { font-size: 13px; color: var(--muted); margin-bottom: 14px; }
.crumbs a { color: var(--accent); }

/* Home */
.hero { background: var(--card); border-radius: 12px; padding: 18px 20px; box-shadow: 0 1px 4px rgba(0,0,0,.06); }
.hero h1 { margin: 0 0 6px; font-size: 22px; }
.hero p { color: var(--muted); margin: 0 0 14px; max-width: 760px; font-size: 13.5px; }
.cats { display: flex; flex-direction: column; gap: 16px; margin-top: 8px; }
.cat h3 { margin: 0 0 8px; font-size: 13px; color: var(--accent2); border-bottom: 2px solid var(--line); padding-bottom: 5px; text-transform: uppercase; letter-spacing: .4px; }
.tool-grid { display: flex; flex-wrap: wrap; gap: 10px; }
.tool-card {
  display: block;
  width: calc((100% - 30px) / 4);
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 10px 12px;
  box-shadow: 0 1px 3px rgba(0,0,0,.04);
  transition: .15s;
}
.tool-card:hover { border-color: var(--accent); transform: translateY(-1px); box-shadow: 0 4px 12px rgba(31,111,235,.15); }
.tool-card .tn { font-weight: 600; font-size: 13.5px; }
.tool-card .td { font-size: 12px; color: var(--muted); margin-top: 2px; }
@media (max-width: 980px) { .tool-card { width: calc((100% - 10px) / 2); } }
@media (max-width: 560px) { .tool-card { width: 100%; } }

/* Calculator page */
.page-head { background: var(--card); border-radius: 12px 12px 0 0; padding: 20px 24px; border: 1px solid var(--line); border-bottom: none; }
.page-head h1 { margin: 0 0 6px; font-size: 22px; }
.page-head p { color: var(--muted); margin: 0; }
.calc-body { background: var(--card); border-radius: 0 0 12px 12px; padding: 22px 24px; border: 1px solid var(--line); }
.form-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(230px, 1fr)); gap: 14px 22px; }
.field { display: flex; flex-direction: column; gap: 4px; }
.field label { font-size: 13px; color: var(--muted); font-weight: 500; }
.field input, .field select {
  padding: 9px 10px;
  border: 1px solid var(--line);
  border-radius: 7px;
  font-size: 14px;
  background: #fff;
  color: var(--ink);
}
.field input:focus, .field select:focus { outline: none; border-color: var(--accent); box-shadow: 0 0 0 2px rgba(31,111,235,.15); }
.field .hint { font-size: 11.5px; color: #97a3b0; }
.actions { margin: 20px 0 6px; display: flex; gap: 12px; }
.btn {
  border: none; border-radius: 7px; padding: 10px 22px; font-size: 14px; font-weight: 600; cursor: pointer;
}
.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { background: var(--accent2); }
.btn-ghost { background: #eef1f5; color: var(--ink); }
.btn-ghost:hover { background: #e2e7ee; }

.result-box { margin-top: 22px; background: var(--res); border: 1px solid #b9d8ff; border-radius: 10px; padding: 18px 20px; }
.result-box h3 { margin: 0 0 12px; font-size: 15px; color: var(--accent2); }
.res-row { display: flex; justify-content: space-between; gap: 16px; padding: 7px 0; border-bottom: 1px dashed #cfe3ff; }
.res-row:last-child { border-bottom: none; }
.res-row .k { color: var(--muted); font-size: 13.5px; }
.res-row .v { font-weight: 600; font-variant-numeric: tabular-nums; }
.res-row .v .u { font-weight: 400; color: #6b7a8a; font-size: 12px; margin-left: 4px; }
.note-box { margin-top: 16px; background: var(--warn); border: 1px solid #ffd9a0; border-radius: 9px; padding: 12px 16px; font-size: 13px; color: #7a5a1f; }

/* inspection table */
table.insp { border-collapse: collapse; width: 100%; font-size: 13.5px; margin-top: 6px; }
table.insp th, table.insp td { border: 1px solid var(--line); padding: 8px 10px; text-align: left; vertical-align: top; }
table.insp th { background: #eef4ff; color: var(--accent2); }
table.insp tr:nth-child(even) td { background: #fafcff; }

.table-scroll { overflow-x: auto; }
.sin-table { font-size: 12px; }
.sin-table td, .sin-table th { padding: 3px 6px; }

.footer { text-align: center; color: var(--muted); font-size: 12.5px; padding: 30px 18px 40px; }

/* SVG diagram */
.diagram { margin: 14px 0; background: #fbfdff; border: 1px solid var(--line); border-radius: 10px; padding: 10px; }
.diagram svg { width: 100%; height: auto; display: block; }

@media (max-width: 640px) {
  .brand small { display: none; }
  .app-header .inner { gap: 8px; height: 52px; }
  .btn-top { padding: 6px 10px; font-size: 12px; }
}

/* Tabs */
.tabs { display: flex; gap: 8px; margin: 18px 0 4px; flex-wrap: wrap; }
.tab { background: #fff; border: 1px solid var(--line); color: var(--muted); padding: 9px 16px; border-radius: 8px 8px 0 0; cursor: pointer; font-size: 14px; font-weight: 600; }
.tab.active { background: var(--accent); border-color: var(--accent); color: #fff; }

/* result status */
.res-row.ok .v { color: var(--eng); font-weight: 700; }
.res-row.bad .v { color: #c0392b; font-weight: 700; }

/* Unit chip */
.u-chip { font-size: 11px; color: var(--accent2); background: #eef4ff; border: 1px solid #cfe0ff; border-radius: 4px; padding: 1px 6px; margin-left: 6px; align-self: center; }
.field { position: relative; }
input.invalid, select.invalid { border-color: #c0392b !important; background: #fff6f5; }

/* Formula box */
.formula-box { margin-top: 16px; background: #f7fafc; border: 1px solid var(--line); border-left: 3px solid var(--accent); border-radius: 8px; padding: 12px 16px; font-size: 13px; color: #33414f; }
.formula-box h4 { margin: 0 0 8px; font-size: 13px; color: var(--accent2); }
.formula-box code, .formula-box pre { font-family: "SFMono-Regular", Consolas, "Liberation Mono", monospace; background: #eef3f8; padding: 2px 6px; border-radius: 4px; font-size: 12.5px; display: block; margin: 4px 0; white-space: pre-wrap; }

/* Print */
@media print {
  .app-header, .actions, .u-chip, .note-box, .footer { display: none !important; }
  body { background: #fff; }
  .container { margin: 0; }
  .calc-body, .page-head { box-shadow: none; border: none; }
  .result-box { border: 1px solid #999; }
}