:root {
  --blue: #1a5fb4;
  --blue-dark: #12407d;
  --blue-light: #eaf2fb;
  --accent: #e8a33d;
  --ink: #1f2937;
  --muted: #5b6472;
  --line: #dde3ea;
  --bg: #f4f7fa;
  --card: #ffffff;
  --ok: #1f9d55;
  --warn: #d97706;
  --bad: #c0392b;
  --shadow: 0 2px 10px rgba(16, 42, 80, .08);
  --radius: 10px;
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  font-family: "Segoe UI", "PingFang SC", "Microsoft YaHei", "Helvetica Neue", Arial, sans-serif;
  background: var(--bg);
  color: var(--ink);
  line-height: 1.55;
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

/* ================= TOP BAR ================= */
.topbar {
  background: linear-gradient(120deg, var(--blue-dark), #1d6fce);
  color: #fff;
  box-shadow: 0 2px 12px rgba(0,0,0,.18);
  position: sticky; top: 0; z-index: 50;
}
.topbar-inner {
  max-width: 1180px; margin: 0 auto; padding: 10px 20px;
  display: flex; align-items: center; gap: 14px; flex-wrap: wrap;
}
.brand {
  display: flex; align-items: center; gap: 10px; font-weight: 700; font-size: 1.05rem; flex: 1 1 auto;
  cursor: default;
}
.brand .logo {
  width: 34px; height: 34px; border-radius: 8px;
  background: var(--accent); color: var(--blue-dark);
  display: grid; place-items: center; font-weight: 800; font-size: 1.15rem;
}
.top-actions { display: flex; align-items: center; gap: 8px; }
.top-actions a {
  display: inline-flex; align-items: center; gap: 6px;
  background: rgba(255,255,255,.16); color: #fff; text-decoration: none;
  padding: 7px 13px; border-radius: 8px; font-size: .9rem; font-weight: 600;
  border: 1px solid rgba(255,255,255,.14); transition: background .15s;
}
.top-actions a:hover { background: rgba(255,255,255,.3); }
.top-actions .btn-homepage { background: var(--accent); color: var(--blue-dark); border-color: var(--accent); }
.top-actions .btn-homepage:hover { filter: brightness(1.06); }
.lang-sel {
  padding: 6px 8px; border-radius: 8px; border: none; font-size: .85rem;
  background: rgba(255,255,255,.2); color: #fff; cursor: pointer; font-weight: 600;
}
.lang-sel option { color: var(--ink); background: #fff; }

/* ================= NAV ================= */
.mainnav { background: #fff; border-bottom: 1px solid var(--line); }
.mainnav ul {
  max-width: 1180px; margin: 0 auto; padding: 0 20px; list-style: none;
  display: flex; flex-wrap: wrap; gap: 4px;
}
.mainnav a {
  display: block; padding: 12px 14px; text-decoration: none; color: var(--muted);
  font-weight: 600; font-size: .92rem; border-bottom: 3px solid transparent; border-radius: 6px 6px 0 0;
}
.mainnav a:hover { color: var(--blue); background: var(--blue-light); }
.mainnav a.active { color: var(--blue); border-bottom-color: var(--blue); }

/* ================= LAYOUT / CARDS ================= */
.wrap { max-width: 1180px; margin: 0 auto; padding: 26px 20px 40px; flex: 1; }
.page-head { margin-bottom: 22px; }
.page-head h1 { margin: 0 0 6px; font-size: 1.7rem; }
.page-head p { margin: 0; color: var(--muted); }

.cards { display: grid; grid-template-columns: repeat(auto-fit, minmax(250px, 1fr)); gap: 18px; }
.card {
  background: var(--card); border: 1px solid var(--line); border-radius: var(--radius);
  box-shadow: var(--shadow); padding: 22px; display: flex; flex-direction: column; gap: 10px;
  text-decoration: none; color: inherit; transition: transform .12s, box-shadow .12s;
}
.card:hover { transform: translateY(-3px); box-shadow: 0 8px 22px rgba(16,42,80,.14); }
.card .ico {
  width: 44px; height: 44px; border-radius: 10px; display: grid; place-items: center;
  font-size: 1.5rem; background: var(--blue-light); color: var(--blue);
}
.card h3 { margin: 0; font-size: 1.05rem; }
.card p { margin: 0; color: var(--muted); font-size: .92rem; flex: 1; }
.card .go { color: var(--blue); font-weight: 700; font-size: .9rem; }

.panel {
  background: var(--card); border: 1px solid var(--line); border-radius: var(--radius);
  box-shadow: var(--shadow); padding: 22px; margin-bottom: 20px;
}
.panel h2 { margin: 0 0 14px; font-size: 1.2rem; }

/* ================= TABS ================= */
.tabs { display: flex; gap: 6px; flex-wrap: wrap; margin-bottom: 20px; }
.tabs button {
  padding: 10px 18px; border: 1px solid var(--line); background: #fff; border-radius: 8px;
  font-weight: 700; font-size: .92rem; color: var(--muted); cursor: pointer;
}
.tabs button.active { background: var(--blue); color: #fff; border-color: var(--blue); }
.tabpane { display: none; }
.tabpane.active { display: block; }

/* ================= FORM ================= */
.grid2 { display: grid; grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); gap: 14px; }
.field label { display: block; font-size: .84rem; font-weight: 700; color: var(--muted); margin-bottom: 5px; }
.field input, .field select {
  width: 100%; padding: 9px 11px; border: 1px solid var(--line); border-radius: 8px;
  font-size: .95rem; background: #fff;
}
.field input:focus, .field select:focus { outline: 2px solid var(--blue-light); border-color: var(--blue); }
.field .hint { font-size: .76rem; color: var(--muted); margin-top: 4px; }

.btn-row { margin-top: 18px; display: flex; gap: 10px; flex-wrap: wrap; }
.btn {
  padding: 11px 22px; border: none; border-radius: 8px; font-weight: 700; font-size: .95rem;
  cursor: pointer; background: var(--blue); color: #fff; transition: background .15s;
}
.btn:hover { background: var(--blue-dark); }
.btn.secondary { background: #e6ecf3; color: var(--ink); }
.btn.secondary:hover { background: #d6e0ec; }

/* ================= RESULTS ================= */
.result {
  margin-top: 20px; padding: 16px 18px; border-radius: 10px; background: var(--blue-light);
  border: 1px solid #c9dcf3; display: none;
}
.result.show { display: block; }
.result .rrow { display: flex; justify-content: space-between; gap: 12px; padding: 7px 0; border-bottom: 1px dashed rgba(26,95,180,.18); }
.result .rrow:last-child { border-bottom: none; }
.result .rk { color: var(--muted); font-size: .9rem; }
.result .rv { font-weight: 800; color: var(--blue-dark); font-size: 1.05rem; }
.result .big { font-size: 1.3rem; }
.status { font-weight: 800; font-size: .92rem; margin-top: 8px; padding-top: 8px; border-top: 1px solid rgba(26,95,180,.18); }
.status.ok { color: var(--ok); }
.status.warn { color: var(--warn); }
.status.bad { color: var(--bad); }

.note {
  margin-top: 16px; padding: 12px 14px; border-radius: 8px; font-size: .85rem;
  background: #fff7e6; border: 1px solid #f0dcae; color: #7a5a12;
}

/* ================= TABLES ================= */
.data-table { width: 100%; border-collapse: collapse; font-size: .9rem; }
.data-table th, .data-table td { border: 1px solid var(--line); padding: 9px 11px; text-align: left; }
.data-table th { background: var(--blue-light); color: var(--blue-dark); font-weight: 700; }
.data-table tbody tr:nth-child(even) { background: #f8fafc; }
.data-table tbody tr:hover { background: #eef4fb; }
.table-tools { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; margin-bottom: 14px; }
.table-tools input[type=search] { min-width: 220px; padding: 8px 11px; border: 1px solid var(--line); border-radius: 8px; }
.badge { display: inline-block; padding: 1px 8px; border-radius: 6px; font-size: .78rem; font-weight: 800; }

/* ================= GUIDE / FOOTER ================= */
.guide ol, .guide ul { margin: 4px 0; padding-left: 22px; color: var(--muted); }
.guide li { margin-bottom: 7px; }
.guide p { color: var(--muted); margin: 8px 0; }
.guide h3 { margin: 20px 0 8px; font-size: 1.04rem; color: var(--blue-dark); }
.guide h4 { margin: 18px 0 4px; font-size: .96rem; color: var(--blue); }
.formula {
  font-family: "Cambria Math", "Times New Roman", Georgia, serif;
  background: var(--blue-light); border: 1px solid #c9dcf3; border-radius: 8px;
  padding: 8px 13px; margin: 6px 0; color: var(--blue-dark);
  font-weight: 700; font-size: 1.02rem;
}
.formula small { font-weight: 600; color: var(--muted); display: block; margin-top: 2px; }
.figrow { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; margin: 10px 0 4px; }
.figrow.figs3 { grid-template-columns: repeat(3, 1fr); }
.steps { display: grid; gap: 10px; margin: 8px 0 2px; }
.step {
  background: var(--card); border: 1px solid var(--line); border-left: 4px solid var(--blue);
  border-radius: 8px; padding: 10px 12px 9px;
}
.step .step-no { display: block; font-weight: 800; color: var(--blue-dark); font-size: .95rem; margin-bottom: 6px; }
.step .step-note { margin: 7px 0 0; color: var(--muted); font-size: .9rem; line-height: 1.5; }
.step .derive { margin: 9px 0 0; padding: 9px 12px; background: rgba(26,95,180,.055); border: 1px dashed rgba(26,95,180,.35); border-radius: 6px; font-size: .88rem; line-height: 1.75; color: var(--ink); white-space: pre-line; }
.step .derive-t { display: block; font-weight: 700; color: var(--blue-dark); font-size: .84rem; letter-spacing: .02em; margin-bottom: 5px; }
.figread { margin: 7px 2px 2px; text-align: left; color: var(--muted); font-size: .86rem; line-height: 1.55; }
.fig {
  background: var(--card); border: 1px solid var(--line); border-radius: 10px;
  padding: 6px 10px 4px; text-align: center;
}
.fig svg { width: 100%; height: auto; max-width: 380px; display: block; margin: 0 auto; }
.fig .cap { font-size: .84rem; font-weight: 700; color: var(--blue-dark); padding: 4px 0 6px; }
.fig .cap small { display: block; font-weight: 500; color: var(--muted); margin-top: 2px; font-size: .78rem; }
@media (max-width: 720px) { .figrow { grid-template-columns: 1fr; } }
/* ================= FORMULA VISUALISATION PLOTS ================= */
.viz-h { margin: 22px 0 6px; font-size: 1.04rem; color: var(--blue-dark); }
.viz-sub { color: var(--muted); font-size: .88rem; margin: 0 0 10px; }
.plots { display: grid; grid-template-columns: repeat(auto-fit, minmax(210px, 1fr)); gap: 12px; }
.plot {
  background: var(--card); border: 1px solid var(--line); border-radius: 10px;
  padding: 8px 8px 6px; text-align: center;
}
.plot svg { width: 100%; height: auto; display: block; margin: 0 auto; }
.plot .pv { min-height: 46px; }
.plot .pl { font-size: .8rem; font-weight: 700; color: var(--blue-dark); padding: 2px 0 3px; text-align: center; }
.plot .pk { font-size: .76rem; font-weight: 800; color: var(--accent); display: block; margin-top: 2px; }
@media (max-width: 720px) { .plots { grid-template-columns: 1fr; } }
.callout {
  background: var(--blue-light); border-left: 4px solid var(--blue);
  padding: 14px 18px; border-radius: 0 10px 10px 0; margin-top: 20px; font-size: .9rem;
}
.site-footer {
  margin-top: auto; background: #16222e; color: #c7d2dd; font-size: .82rem;
  padding: 20px; text-align: center; line-height: 1.7;
}
.site-footer a { color: #e8c98a; }

@media (max-width: 640px) {
  .brand span.sub { display: none; }
  .top-actions { width: 100%; justify-content: flex-end; }
}