/* ─── Design tokens (mirrors shelterland style) ─────────────────── */
  :root {
    color-scheme: light dark;
    --bg:        #101816;
    --surface:   #17211e;
    --surface-2: #20302a;
    --surface-3: #25372f;
    --text:      #f1f7f2;
    --muted:     #b2c2ba;
    --line:      rgba(241, 247, 242, 0.12);
    --accent:    #7fd3b1;
    --accent-dk: #9fdcc4;
    --accent-2:  #d4b16a;
    --mark-filter: invert(92%) sepia(15%) saturate(287%) hue-rotate(103deg) brightness(104%) contrast(94%);
    --shadow:    0 22px 64px rgba(0, 0, 0, 0.28);
    --radius:    12px;
    --radius-sm: 8px;
    --font: "Manrope", "Noto Sans TC", "PingFang TC", "Microsoft JhengHei",
            "Heiti TC", ui-sans-serif, system-ui, -apple-system, sans-serif;
  }
   /* ─── Reset ──────────────────────────────────────────────────────── */
  *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
  html { scroll-behavior: smooth; }
   /* ─── Base ───────────────────────────────────────────────────────── */
  body {
    font-family: var(--font);
    background: radial-gradient(circle at top left, color-mix(in srgb, var(--accent) 11%, transparent), transparent 34rem),
                radial-gradient(circle at 85% 8%, color-mix(in srgb, var(--accent-2) 12%, transparent), transparent 28rem),
                var(--bg);
    color: var(--text);
    line-height: 1.6;
    min-height: 100dvh;
  }
  a { color: inherit; text-decoration: none; }
   /* ─── Header ─────────────────────────────────────────────────────── */
  .site-header {
    position: sticky;
    top: 0;
    z-index: 10;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 1.5rem;
    padding: .9rem clamp(1rem, 4vw, 4rem);
    backdrop-filter: blur(18px);
    background: color-mix(in srgb, var(--bg) 78%, transparent);
    border-bottom: 1px solid var(--line);
  }
  .header-left { display: flex; align-items: center; gap: .75rem; }
  .brand {
    display: inline-flex;
    align-items: center;
    gap: .75rem;
    font-weight: 800;
    font-size: 1.1rem;
    letter-spacing: -.02em;
  }
  .brand-mark {
    width: 2.2rem;
    height: 2.2rem;
    object-fit: contain;
    filter: var(--mark-filter);
  }
  .header-sep { margin: 0 .25rem; opacity: .35; }
  .header-tool {
    font-size: .92rem;
    color: var(--muted);
    font-weight: 500;
  }
  .header-right { display: flex; align-items: center; gap: .75rem; }
  .header-nav {
    display: flex;
    gap: 1.25rem;
    font-size: .88rem;
    color: var(--muted);
  }
  .header-nav a { text-decoration: none; color: var(--muted); }
  .header-nav a:hover { color: var(--text); }
  .theme-toggle {
    width: 2.5rem; height: 2.5rem;
    border: 1px solid var(--line);
    background: color-mix(in srgb, var(--surface) 86%, transparent);
    color: var(--text);
    border-radius: 999px;
    display: grid; place-items: center;
    cursor: pointer;
    backdrop-filter: blur(16px);
  }
  .theme-toggle .theme-icon { grid-area: 1 / 1; width: 1.05rem; height: 1.05rem; fill: none; stroke: currentColor; stroke-width: 1.8; stroke-linecap: round; stroke-linejoin: round; transition: opacity .18s ease, transform .18s ease; }
  .theme-toggle .sun circle { fill: currentColor; stroke: none; }
  .theme-toggle .moon { opacity: 1; transform: scale(1) rotate(0deg); }
  .theme-toggle .sun  { opacity: 0; transform: scale(.7) rotate(-20deg); }
  :root[data-theme="day"] .theme-toggle .moon { opacity: 0; transform: scale(.7) rotate(-20deg); }
  :root[data-theme="day"] .theme-toggle .sun  { opacity: 1; transform: scale(1) rotate(0deg); }
  @media (prefers-color-scheme: light) {
    :root:not([data-theme="night"]) .theme-toggle .moon { opacity: 0; transform: scale(.7) rotate(-20deg); }
    :root:not([data-theme="night"]) .theme-toggle .sun  { opacity: 1; transform: scale(1) rotate(0deg); }
  }
  .mobile-back {
    display: none;
    align-items: center;
    gap: .4rem;
    padding: .5rem clamp(1rem,4vw,2rem);
    font-size: .82rem;
    color: var(--muted);
    border-bottom: 1px solid var(--line);
  }
  .mobile-back a { color: var(--accent); text-decoration: none; }
   /* ─── Main wrapper ───────────────────────────────────────────────── */
  .page {
    width: min(800px, calc(100% - 2rem));
    margin: 0 auto;
    padding: clamp(2.5rem, 5vw, 4rem) 0 5rem;
  }
   /* ─── Page heading ───────────────────────────────────────────────── */
  .page-title {
    font-size: clamp(1.6rem, 4vw, 2.2rem);
    font-weight: 800;
    letter-spacing: -.03em;
    margin-bottom: .5rem;
  }
  .page-subtitle {
    color: var(--muted);
    font-size: .95rem;
    margin-bottom: 2rem;
  }
   /* ─── Category tabs ──────────────────────────────────────────────── */
  .tabs {
    display: flex;
    flex-wrap: wrap;
    gap: .5rem;
    margin-bottom: 2rem;
  }
  .tab-btn {
    padding: .45rem 1.1rem;
    border: 1px solid var(--line);
    border-radius: 999px;
    background: color-mix(in srgb, var(--surface) 80%, transparent);
    color: var(--muted);
    font-family: var(--font);
    font-size: .88rem;
    font-weight: 600;
    cursor: pointer;
    transition: background .15s, color .15s, border-color .15s;
    white-space: nowrap;
  }
  .tab-btn:hover {
    color: var(--text);
    border-color: color-mix(in srgb, var(--accent) 40%, transparent);
  }
  .tab-btn.active {
    background: var(--accent-dk);
    color: #fff;
    border-color: var(--accent-dk);
  }
   /* ─── Converter panel ────────────────────────────────────────────── */
  .panel { display: none; }
  .panel.active { display: block; }
   /* ─── Field grid ─────────────────────────────────────────────────── */
  .fields {
    display: grid;
    /* 2 columns on desktop, 1 on mobile */
    grid-template-columns: repeat(auto-fill, minmax(min(100%, 320px), 1fr));
    gap: 1rem;
  }
   /* ─── Individual field ───────────────────────────────────────────── */
  .field {
    background: var(--surface);
    border: 1px solid var(--line);
    border-radius: var(--radius);
    padding: 1rem 1.2rem;
    transition: border-color .15s, box-shadow .15s;
  }
  .field:focus-within {
    border-color: color-mix(in srgb, var(--accent) 60%, transparent);
    box-shadow: 0 0 0 3px color-mix(in srgb, var(--accent) 12%, transparent);
  }
  .field label {
    display: block;
    font-size: .78rem;
    font-weight: 700;
    letter-spacing: .05em;
    text-transform: uppercase;
    color: var(--muted);
    margin-bottom: .5rem;
  }
  .field-row {
    display: flex;
    align-items: center;
    gap: .6rem;
  }
  .field input[type="number"] {
    flex: 1;
    min-width: 0;
    background: transparent;
    border: none;
    outline: none;
    color: var(--text);
    font-family: var(--font);
    font-size: 1.35rem;
    font-weight: 700;
    letter-spacing: -.02em;
    /* Hide number spinners for cleaner look */
    -moz-appearance: textfield;
  }
  .field input[type="number"]::-webkit-inner-spin-button,
  .field input[type="number"]::-webkit-outer-spin-button { -webkit-appearance: none; }
   .field-unit {
    font-size: .82rem;
    font-weight: 600;
    color: var(--accent);
    white-space: nowrap;
  }
   /* ─── Temperature note ───────────────────────────────────────────── */
  .panel-note {
    margin-top: 1.25rem;
    padding: .85rem 1.1rem;
    background: color-mix(in srgb, var(--accent-dk) 20%, transparent);
    border: 1px solid color-mix(in srgb, var(--accent-dk) 40%, transparent);
    border-radius: var(--radius-sm);
    font-size: .82rem;
    color: var(--muted);
  }
  .panel-note strong { color: var(--text); }
   /* ─── Footer ─────────────────────────────────────────────────────── */
  .site-footer {
    border-top: 1px solid var(--line);
    padding: 2rem clamp(1rem, 4vw, 4rem);
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: space-between;
    gap: 1rem;
    font-size: .82rem;
    color: var(--muted);
  }
  .site-footer a:hover { color: var(--text); }
   /* ─── Responsive ─────────────────────────────────────────────────── */
  @media (prefers-color-scheme: light) {
    :root:not([data-theme="night"]) {
      color-scheme: light;
      --bg: #f8f5ee; --surface: #fffdf8; --surface-2: #eee7da; --surface-3: #e5dccb;
      --text: #26312d; --muted: #64746c; --line: rgba(38,49,45,.12);
      --accent: #3f8068; --accent-dk: #34745f; --shadow: 0 18px 52px rgba(72,80,67,.13);
      --mark-filter: none;
    }
  }
  :root[data-theme="day"] {
    color-scheme: light;
    --bg: #f8f5ee; --surface: #fffdf8; --surface-2: #eee7da; --surface-3: #e5dccb;
    --text: #26312d; --muted: #64746c; --line: rgba(38,49,45,.12);
    --accent: #3f8068; --accent-dk: #34745f; --shadow: 0 18px 52px rgba(72,80,67,.13);
    --mark-filter: none;
  }
  @media (max-width: 520px) {
    .fields { grid-template-columns: 1fr; }
    .header-nav { display: none; }
    .mobile-back { display: flex; }
  }