/* ==========================================================================
   basisthread.com — shared single-purpose calculator shell.
   Used by every simple tool (Quick Convert, Air-side heat, Water-side
   heat, Air changes, Duct velocity). Psychrometrics has its own richer
   app-shell (tabs/history/settings) and doesn't use this file.
   Responsive by nature of being a centered card with relative sizing --
   no breakpoint-specific layout swap needed the way the tabbed app-shell
   requires.
   ========================================================================== */

body {
  min-height: 100vh;
  display: flex;
  justify-content: center;
  padding: var(--space-7) var(--space-5);
  background:
    linear-gradient(var(--color-paper-dim) 1px, transparent 1px),
    linear-gradient(90deg, var(--color-paper-dim) 1px, transparent 1px);
  background-size: 32px 32px;
}

.bt-page {
  width: 100%;
  max-width: 560px;
}

.bt-back {
  display: inline-flex; align-items: center; gap: var(--space-2);
  margin-bottom: var(--space-5); font-size: 0.875rem;
}
.bt-back a { color: var(--color-accent-strong); text-decoration: none; }
.bt-back a:hover { text-decoration: underline; }

.bt-card {
  background: var(--color-paper);
  border: 1px solid var(--color-graphite);
  border-radius: 10px;
  overflow: hidden;
  box-shadow: 0 24px 48px rgba(27, 31, 35, 0.1);
}

.bt-card-header {
  padding: var(--space-6) var(--space-6) var(--space-5);
  border-bottom: 1px solid var(--color-steel-light);
}
.bt-eyebrow {
  display: block; font-family: var(--font-mono); font-size: 0.6875rem;
  letter-spacing: 0.08em; color: var(--color-accent); margin-bottom: var(--space-2);
}
.bt-card-header h1 { margin: 0 0 var(--space-2); font-size: 1.5rem; }
.bt-card-header p { margin: 0; color: var(--color-graphite); font-size: 0.9375rem; }

.bt-card-body { padding: var(--space-6); }

.bt-field { margin-bottom: var(--space-5); }
.bt-field label {
  display: block; font-size: 0.8125rem; font-weight: 600; margin-bottom: var(--space-2);
}
.bt-field select,
.bt-field input {
  width: 100%; min-height: 44px;
  border: 1px solid var(--color-graphite);
  background: var(--color-white);
  font-family: var(--font-mono); font-size: 1rem; color: var(--color-charcoal);
  padding: 0 0.625rem;
}
.bt-field-hint { display: block; margin-top: var(--space-2); font-size: 0.75rem; color: var(--color-steel); }
.bt-input-row { display: flex; flex-wrap: wrap; gap: var(--space-4); }
.bt-input-row .bt-field { flex: 1 1 140px; min-width: 0; }
.bt-input-row-3 .bt-field { flex-basis: 30%; }

.bt-swap-row {
  display: grid; grid-template-columns: 1fr auto 1fr; gap: var(--space-3);
  align-items: end; margin-bottom: var(--space-5);
}
.bt-swap-btn {
  width: 44px; height: 44px; border: 1px solid var(--color-graphite);
  background: var(--color-paper); color: var(--color-charcoal);
  font-size: 1.125rem; cursor: pointer;
}
.bt-swap-btn:hover { background: var(--color-accent-wash); }

.bt-result {
  margin-top: var(--space-6);
  padding: var(--space-5);
  background: var(--color-charcoal);
  color: var(--color-paper);
}
.bt-result-label {
  display: block; font-family: var(--font-mono); font-size: 0.6875rem;
  letter-spacing: 0.06em; color: var(--color-steel-light); margin-bottom: var(--space-3);
}
.bt-result-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 1px; background: rgba(255,255,255,0.15); }
.bt-result-cell { padding: var(--space-4); background: var(--color-charcoal); }
.bt-result-cell .label { font-family: var(--font-mono); font-size: 0.6875rem; color: var(--color-steel-light); display: block; margin-bottom: var(--space-1); }
.bt-result-value {
  font-family: var(--font-mono); font-weight: 600; font-size: 1.75rem; line-height: 1.15;
  color: var(--color-white); word-break: break-word;
}
.bt-result-unit { font-size: 0.8125rem; color: var(--color-accent-bright); margin-left: var(--space-1); }
.bt-result-formula { margin-top: var(--space-4); font-family: var(--font-mono); font-size: 0.75rem; color: var(--color-steel-light); }
.bt-result-error { color: #F2B8B5; font-size: 0.9375rem; }

.bt-actions { display: flex; flex-wrap: wrap; gap: var(--space-3); align-items: center; margin-top: var(--space-5); }
.bt-btn {
  min-height: 40px; padding: 0 var(--space-4);
  border: 1px solid var(--color-graphite); background: var(--color-white); color: var(--color-charcoal);
  font-family: var(--font-sans); font-size: 0.875rem; font-weight: 600; cursor: pointer;
}
.bt-btn:hover { background: var(--color-accent-wash); border-color: var(--color-accent); }
.bt-btn-quiet { border-color: transparent; background: none; color: var(--color-steel); }
.bt-btn-quiet:hover { color: var(--color-charcoal); background: none; }
.bt-copy-status { font-size: 0.8125rem; color: var(--color-steel); }

.bt-disclaimer { margin-top: var(--space-5); font-size: 0.8125rem; color: var(--color-steel); }

@media (max-width: 480px) {
  body { padding: 0; }
  .bt-page { max-width: none; }
  .bt-back { margin: var(--space-4) var(--space-5) 0; }
  .bt-card { border: 0; border-radius: 0; box-shadow: none; }
}