/* ── Reset & Base ── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --success: #16a34a;
  --error: #dc2626;
  --bg: #f8fafc;
  --card-bg: #ffffff;
  --text: #1e293b;
  --muted: #64748b;
  --border: #e2e8f0;
  --radius: 8px;
  --shadow: 0 1px 3px rgba(0,0,0,.08), 0 1px 2px rgba(0,0,0,.06);
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang TC",
               "Microsoft JhengHei", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

.container {
  max-width: 800px;
  margin: 0 auto;
  padding: 0 1rem;
  width: 100%;
}

/* ── Header ── */
.site-header {
  background: var(--primary);
  color: #fff;
  padding: .75rem 0;
  position: sticky;
  top: 0;
  z-index: 10;
  box-shadow: 0 2px 4px rgba(0,0,0,.15);
}
.site-header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: .5rem;
}
.logo {
  font-size: 1.2rem;
  font-weight: 700;
  color: #fff;
  text-decoration: none;
}
.site-header nav a {
  color: rgba(255,255,255,.85);
  text-decoration: none;
  margin-left: 1rem;
  font-size: .9rem;
  transition: color .15s;
}
.site-header nav a:hover { color: #fff; }

/* ── Main ── */
main.container {
  flex: 1;
  padding-top: 2rem;
  padding-bottom: 3rem;
}
h1 {
  font-size: 1.8rem;
  font-weight: 700;
  color: var(--primary);
  margin-bottom: .25rem;
}
.subtitle {
  color: var(--muted);
  margin-bottom: 1.5rem;
}

/* ── Tabs ── */
.tab-bar {
  display: flex;
  flex-wrap: wrap;
  gap: .5rem;
  margin-bottom: 1.25rem;
}
.tab {
  background: var(--card-bg);
  border: 2px solid var(--border);
  border-radius: var(--radius);
  padding: .45rem 1rem;
  font-size: .9rem;
  cursor: pointer;
  color: var(--muted);
  transition: all .15s;
}
.tab:hover { border-color: var(--primary); color: var(--primary); }
.tab.active {
  background: var(--primary);
  border-color: var(--primary);
  color: #fff;
  font-weight: 600;
}

/* ── Tab Panels ── */
.tab-panel { display: none; }
.tab-panel.active { display: block; }

/* ── Card ── */
.card {
  background: var(--card-bg);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  border: 1px solid var(--border);
  padding: 1.5rem;
  margin-bottom: 1.25rem;
}
.card h2 {
  font-size: 1.05rem;
  font-weight: 600;
  margin-bottom: 1rem;
  color: var(--text);
}

/* ── Inputs ── */
.input-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: .6rem;
  margin-bottom: 1rem;
}
.input-row label {
  font-size: .85rem;
  color: var(--muted);
  min-width: 3.5rem;
}
.input-row input {
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: .45rem .75rem;
  font-size: 1rem;
  width: 8rem;
  transition: border-color .15s;
}
.input-row input:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(37,99,235,.15);
}
.unit {
  color: var(--muted);
  font-size: .9rem;
  white-space: nowrap;
}

/* ── Button ── */
.btn-calc {
  background: var(--primary);
  color: #fff;
  border: none;
  border-radius: var(--radius);
  padding: .55rem 1.5rem;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: background .15s;
}
.btn-calc:hover { background: var(--primary-dark); }
.btn-calc:active { transform: translateY(1px); }

/* ── Result / Error ── */
.result-box {
  margin-top: .75rem;
  padding: .75rem 1rem;
  background: #f0fdf4;
  border-left: 4px solid var(--success);
  border-radius: 4px;
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--success);
  display: none;
}
.result-box.visible { display: block; }

.error-msg {
  margin-top: .5rem;
  color: var(--error);
  font-size: .9rem;
  display: none;
}
.error-msg.visible { display: block; }

/* ── How-to ── */
.how-to-use {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  margin-top: 1.5rem;
  box-shadow: var(--shadow);
}
.how-to-use h2 {
  font-size: 1.1rem;
  margin-bottom: .75rem;
  color: var(--primary);
}
.how-to-use dl { display: grid; grid-template-columns: auto 1fr; gap: .5rem 1rem; }
.how-to-use dt { font-weight: 600; color: var(--text); }
.how-to-use dd { color: var(--muted); }

/* ── Footer ── */
.site-footer {
  background: var(--text);
  color: rgba(255,255,255,.7);
  padding: 1.25rem 0;
  font-size: .85rem;
  margin-top: auto;
}
.site-footer .container {
  display: flex;
  flex-wrap: wrap;
  gap: .5rem;
  justify-content: space-between;
  align-items: center;
}
.site-footer nav a {
  color: rgba(255,255,255,.7);
  text-decoration: none;
}
.site-footer nav a:hover { color: #fff; }

/* ── Responsive ── */
@media (max-width: 600px) {
  h1 { font-size: 1.4rem; }
  .input-row { flex-direction: column; align-items: flex-start; }
  .input-row input { width: 100%; }
  .site-header .container { flex-direction: column; align-items: flex-start; }
  .site-header nav a { margin-left: 0; margin-right: .75rem; }
  .how-to-use dl { grid-template-columns: 1fr; }
}

/* ── Inner pages ── */
.page-content {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 2rem;
  box-shadow: var(--shadow);
  margin-top: 2rem;
  margin-bottom: 3rem;
}
.page-content h1 { margin-bottom: 1rem; }
.page-content h2 { margin-top: 1.5rem; margin-bottom: .5rem; font-size: 1.1rem; color: var(--primary); }
.page-content p, .page-content li { color: var(--muted); margin-bottom: .5rem; }
.page-content ul { padding-left: 1.5rem; }

/* ── Tool Cards (portal) ── */
.tool-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 1.25rem;
  margin-top: 1.5rem;
}
.tool-card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  box-shadow: var(--shadow);
  text-decoration: none;
  color: var(--text);
  display: flex;
  flex-direction: column;
  gap: .5rem;
  transition: box-shadow .15s, border-color .15s;
}
.tool-card:hover { box-shadow: 0 4px 12px rgba(0,0,0,.12); border-color: var(--primary); }
.tool-card .tool-icon { font-size: 2rem; }
.tool-card .tool-name { font-size: 1.1rem; font-weight: 700; color: var(--primary); }
.tool-card .tool-desc { font-size: .9rem; color: var(--muted); line-height: 1.5; }