/* ==========================================================================
   DecisionCalcs — design system v2
   Principles: one accent, hairline borders, tinted layered shadows,
   editorial left-aligned headings, restrained motion (150/260/420ms).
   ========================================================================== */

:root {
  /* ---- color: ink scale ---- */
  --ink-950: #060b16;
  --ink-900: #0a101d;
  --ink-800: #101a2e;
  --ink-700: #1c2740;
  --ink-600: #2e3b58;
  --slate-500: #62708c;
  --slate-400: #8b97ad;
  --slate-300: #b9c2d3;

  /* ---- color: surfaces ---- */
  --bg: #f7f9fc;
  --surface: #ffffff;
  --surface-2: #fbfcfe;
  --line: #e8ecf3;
  --line-strong: #d9dfe9;

  /* ---- color: single accent + semantic ---- */
  --accent: #2456e6;
  --accent-deep: #1a44c2;
  --accent-soft: #edf2fe;
  --ring: rgba(36, 86, 230, 0.15);
  --mint: #0ba57d;
  --mint-deep: #067a5b;
  --mint-soft: #e6f7f1;
  --rose: #d92d54;
  --rose-deep: #b31f42;
  --rose-soft: #fceef2;

  /* ---- type: single premium sans (Apple/Stripe/Linear register) ---- */
  --font-ui: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  --font-display: var(--font-ui);

  /* ---- shape ---- */
  --r-sm: 10px;
  --r-md: 14px;
  --r-lg: 20px;

  /* ---- elevation (ink-tinted, layered) ---- */
  --shadow-1: 0 1px 2px rgba(16, 24, 40, 0.04), 0 1px 3px rgba(16, 24, 40, 0.05);
  --shadow-2: 0 2px 4px rgba(16, 24, 40, 0.04), 0 12px 28px -8px rgba(16, 24, 40, 0.11);
  --shadow-3: 0 4px 8px rgba(16, 24, 40, 0.05), 0 32px 64px -16px rgba(16, 24, 40, 0.18);

  /* ---- motion ---- */
  --dur-1: 150ms;
  --dur-2: 260ms;
  --dur-3: 420ms;
  --ease: cubic-bezier(0.2, 0.8, 0.2, 1);
}

/* ---------- reset ---------- */
*, *::before, *::after { box-sizing: border-box; }
* { margin: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--font-ui);
  background: var(--bg);
  color: var(--ink-900);
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}
img, svg { display: block; }
button { font: inherit; cursor: pointer; }
input, select { font: inherit; }
a { color: inherit; }
::selection { background: var(--accent); color: #fff; }

:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

.container { width: min(1120px, 100% - 2.5rem); margin-inline: auto; }
#calculators, #panel, #learn { scroll-margin-top: 84px; }

/* ==========================================================================
   NAV — quiet glass, hairline seam
   ========================================================================== */
.nav {
  position: sticky; top: 0; z-index: 50;
  background: rgba(6, 11, 22, 0.82);
  backdrop-filter: saturate(150%) blur(16px);
  -webkit-backdrop-filter: saturate(150%) blur(16px);
  border-bottom: 1px solid rgba(255, 255, 255, 0.06);
}
.nav-inner { display: flex; align-items: center; justify-content: space-between; height: 60px; }
.brand { display: inline-flex; align-items: center; gap: 10px; text-decoration: none; }
.brand-mark {
  width: 30px; height: 30px; display: grid; place-items: center;
  color: #fff; background: linear-gradient(150deg, #3364f0, var(--accent-deep));
  border-radius: 8px;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.18), 0 2px 8px rgba(36, 86, 230, 0.35);
}
.brand-mark svg { width: 17px; height: 17px; }
.brand-name { font-weight: 700; letter-spacing: -0.02em; font-size: 1.02rem; color: #fff; }
.brand-tld { color: var(--slate-400); font-weight: 500; }
.nav-links { display: flex; align-items: center; gap: 1.6rem; }
.nav-links a {
  text-decoration: none; color: var(--slate-300); font-size: 0.9rem; font-weight: 500;
  transition: color var(--dur-1) var(--ease);
}
.nav-links a:hover { color: #fff; }
.nav-cta {
  color: #fff !important; background: var(--accent);
  padding: 0.48rem 1rem; border-radius: 999px; font-weight: 600 !important;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.16);
  transition: background var(--dur-1) var(--ease) !important;
}
.nav-cta:hover { background: var(--accent-deep); }
@media (max-width: 640px) { .nav-links a:not(.nav-cta) { display: none; } }

/* ==========================================================================
   HERO — deep ink, engineered dot grid, one restrained glow
   ========================================================================== */
.hero {
  position: relative; overflow: hidden;
  background: linear-gradient(180deg, var(--ink-900) 0%, var(--ink-950) 100%);
  color: #fff;
  padding: clamp(2rem, 3.6vw, 2.7rem) 0 clamp(2.2rem, 3.8vw, 2.9rem);
}
.hero::before {
  content: ""; position: absolute; inset: 0;
  background-image: radial-gradient(rgba(255, 255, 255, 0.055) 1px, transparent 1px);
  background-size: 26px 26px;
  mask-image: linear-gradient(180deg, rgba(0,0,0,0.9), transparent 75%);
  -webkit-mask-image: linear-gradient(180deg, rgba(0,0,0,0.9), transparent 75%);
  pointer-events: none;
}
.hero-glow {
  position: absolute; top: -45%; left: 50%; transform: translateX(-50%);
  width: 820px; height: 420px;
  background: radial-gradient(50% 50% at 50% 50%, rgba(36, 86, 230, 0.26), transparent 70%);
  pointer-events: none;
}
.hero-inner { position: relative; text-align: center; max-width: 860px; margin-inline: auto; }
.hero-title {
  font-family: var(--font-display);
  font-weight: 750; letter-spacing: -0.032em;
  font-size: clamp(2rem, 4.3vw, 3.15rem);
  line-height: 1.08; margin-bottom: 0.7rem;
}
.hero-title-accent {
  background: linear-gradient(92deg, #86a7ff 0%, #4d7dff 55%, #6d8fff 100%);
  -webkit-background-clip: text; background-clip: text;
  -webkit-text-fill-color: transparent; color: #5d86ff;
}
.hero-sub {
  color: var(--slate-300); font-size: clamp(0.95rem, 1.8vw, 1.08rem);
  max-width: 640px; margin: 0 auto 1.25rem; line-height: 1.6;
  text-wrap: balance;
}
.hero-actions { display: flex; gap: 0.7rem; justify-content: center; flex-wrap: wrap; margin-bottom: 1.1rem; }
@media (max-width: 430px) {
  .hero-actions { flex-direction: column; align-items: stretch; max-width: 300px; margin-inline: auto; margin-bottom: 1.2rem; }
}
.btn {
  display: inline-flex; align-items: center; justify-content: center;
  padding: 0.8rem 1.45rem; border-radius: 999px; border: none;
  font-weight: 600; font-size: 0.95rem; text-decoration: none;
  transition: transform var(--dur-2) var(--ease), box-shadow var(--dur-2) var(--ease), background var(--dur-2) var(--ease);
}
.btn:active { transform: translateY(0) scale(0.99); }
.btn-primary {
  background: var(--accent); color: #fff;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.18), 0 6px 20px -4px rgba(36, 86, 230, 0.55);
}
.btn-primary:hover { background: var(--accent-deep); transform: translateY(-1px); box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.18), 0 10px 26px -4px rgba(36, 86, 230, 0.6); }
.btn-ghost { background: rgba(255, 255, 255, 0.07); color: #fff; border: 1px solid rgba(255, 255, 255, 0.14); }
.btn-ghost:hover { background: rgba(255, 255, 255, 0.12); transform: translateY(-1px); }
.hero-trust { color: var(--slate-400); font-size: 0.82rem; font-weight: 500; letter-spacing: 0.005em; }

/* ==========================================================================
   SECTIONS — editorial, left-aligned, kicker labels
   ========================================================================== */
.section { padding: clamp(3.5rem, 7vw, 5.5rem) 0; }
.section-panel { padding-top: 1rem; }
#calculators { padding-top: clamp(1.6rem, 3vw, 2.1rem); padding-bottom: clamp(2.25rem, 4vw, 3rem); }
.section-head { margin-bottom: 1.4rem; max-width: 62ch; }
.section-kicker {
  display: block; font-size: 0.72rem; font-weight: 700;
  letter-spacing: 0.12em; text-transform: uppercase; color: var(--accent);
  margin-bottom: 0.6rem;
}
.section-head h2 {
  font-family: var(--font-display); font-weight: 700; letter-spacing: -0.026em;
  font-size: clamp(1.5rem, 3vw, 2.05rem); margin-bottom: 0.35rem;
}
.section-head p { color: var(--slate-500); font-size: 0.95rem; }
.cat-row {
  list-style: none; padding: 0; margin-top: 0.7rem;
  display: flex; flex-wrap: wrap; gap: 0.45rem;
}
.cat-row li {
  font-size: 0.78rem; font-weight: 550; color: var(--slate-500);
  background: var(--surface); border: 1px solid var(--line);
  padding: 0.28rem 0.7rem; border-radius: 999px;
}

/* ==========================================================================
   CALCULATOR CARDS — even grid, one featured treatment, quiet hover
   ========================================================================== */
.card-grid { display: grid; gap: 0.85rem; grid-template-columns: 1fr; }
@media (min-width: 560px) { .card-grid { grid-template-columns: repeat(2, 1fr); } }
@media (min-width: 900px) { .card-grid { grid-template-columns: repeat(3, 1fr); } }

.calc-card {
  position: relative; text-align: left;
  display: flex; flex-direction: column; gap: 0.55rem;
  background: var(--surface); border: 1px solid var(--line);
  border-radius: var(--r-md); padding: 1.3rem 1.25rem 1.4rem;
  box-shadow: var(--shadow-1);
  transition: transform var(--dur-2) var(--ease), box-shadow var(--dur-2) var(--ease), border-color var(--dur-2) var(--ease);
}
.calc-card:not(.is-soon):hover { transform: translateY(-3px); box-shadow: var(--shadow-2); border-color: var(--line-strong); }
.calc-card:not(.is-soon):active { transform: translateY(-1px); transition-duration: var(--dur-1); }
.calc-card:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.calc-card.active { border-color: var(--accent); box-shadow: 0 0 0 1px var(--accent), var(--shadow-2); }

/* flagship: CommissionCheck */
.calc-card.is-featured {
  background: linear-gradient(180deg, #f5f8ff 0%, #ffffff 60%);
}
.calc-card.is-featured::before {
  content: ""; position: absolute; top: -1px; left: 14px; right: 14px; height: 2px;
  background: linear-gradient(90deg, transparent, var(--accent), transparent);
  border-radius: 2px;
}
.card-icon {
  width: 40px; height: 40px; border-radius: 11px;
  display: grid; place-items: center;
  background: var(--accent-soft); color: var(--accent);
  transition: transform var(--dur-2) var(--ease);
}
.calc-card:not(.is-soon):hover .card-icon { transform: translateY(-2px); }
.card-icon svg { width: 21px; height: 21px; }
.card-title { font-weight: 650; font-size: 0.98rem; letter-spacing: -0.011em; }
.card-desc { color: var(--slate-500); font-size: 0.84rem; line-height: 1.5; }
.card-badge {
  position: absolute; top: 0.95rem; right: 0.95rem;
  font-size: 0.64rem; font-weight: 700; letter-spacing: 0.08em; text-transform: uppercase;
  background: var(--accent); color: #fff;
  padding: 0.22rem 0.58rem; border-radius: 999px;
}

/* compact mobile cards: icon-left rows for better density */
@media (max-width: 559px) {
  .calc-card {
    display: grid; grid-template-columns: 40px 1fr; grid-template-rows: auto auto;
    column-gap: 0.9rem; row-gap: 0.15rem; align-items: start;
    padding: 1.05rem 1.1rem;
  }
  .card-icon { grid-row: 1 / 3; margin-top: 2px; }
  .card-desc { font-size: 0.8rem; }
  .card-badge { top: 0.8rem; right: 0.8rem; }
  .calc-card.is-featured .card-title { padding-right: 4.6rem; }
}

/* ---------- coming soon: quiet strip, not competing with real tools ---------- */
.soon-row { margin-top: 2.2rem; display: flex; flex-direction: column; gap: 0.8rem; }
.soon-label {
  font-size: 0.72rem; font-weight: 700; letter-spacing: 0.12em;
  text-transform: uppercase; color: var(--slate-500);
}
.soon-grid { display: grid; gap: 0.7rem; grid-template-columns: repeat(2, 1fr); }
@media (min-width: 720px) { .soon-grid { grid-template-columns: repeat(4, 1fr); } }
.soon-card {
  display: flex; align-items: center; gap: 0.7rem;
  border: 1px dashed var(--line-strong); border-radius: var(--r-sm);
  padding: 0.75rem 0.9rem;
  color: var(--slate-500); font-size: 0.85rem; font-weight: 550;
  background: transparent;
}
.soon-card svg { width: 17px; height: 17px; color: var(--slate-400); flex: none; }

/* ==========================================================================
   ACTIVE CALCULATOR PANEL
   ========================================================================== */
.calc-panel {
  background: var(--surface); border: 1px solid var(--line);
  border-radius: var(--r-lg); box-shadow: var(--shadow-2);
  padding: clamp(1.5rem, 3.4vw, 2.5rem);
  animation: panelIn var(--dur-3) var(--ease);
}
.calc-panel[hidden] { display: none; }
@keyframes panelIn {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: none; }
}
.panel-head {
  display: flex; align-items: flex-start; justify-content: space-between; gap: 1rem;
  padding-bottom: 1.5rem; margin-bottom: 1.75rem; border-bottom: 1px solid var(--line);
}
.panel-kicker {
  display: inline-block; font-size: 0.7rem; font-weight: 700;
  letter-spacing: 0.11em; text-transform: uppercase; color: var(--accent);
  margin-bottom: 0.4rem;
}
.panel-title { font-family: var(--font-display); font-weight: 700; font-size: clamp(1.3rem, 2.8vw, 1.65rem); letter-spacing: -0.024em; }
.panel-sub { color: var(--slate-500); font-size: 0.92rem; margin-top: 0.35rem; max-width: 56ch; line-height: 1.6; }
.btn-reset {
  flex: none; background: transparent; color: var(--slate-500);
  border: 1px solid var(--line-strong); border-radius: 999px;
  padding: 0.4rem 0.95rem; font-size: 0.83rem; font-weight: 600;
  transition: color var(--dur-1) var(--ease), border-color var(--dur-1) var(--ease), background var(--dur-1) var(--ease);
}
.btn-reset:hover { color: var(--ink-800); border-color: var(--slate-400); background: var(--surface-2); }

.panel-body { display: grid; gap: 2rem; min-width: 0; }
@media (min-width: 880px) {
  .panel-body { grid-template-columns: minmax(0, 5fr) minmax(0, 6fr); gap: 2.75rem; align-items: start; }
}

/* ---------- form ---------- */
.panel-form { display: flex; flex-direction: column; gap: 1.1rem; min-width: 0; }
.field-row { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: 0.9rem; min-width: 0; }
@media (max-width: 480px) { .field-row { grid-template-columns: 1fr; gap: 1.1rem; } }
.field { display: flex; flex-direction: column; gap: 0.4rem; min-width: 0; }
.field > label { font-size: 0.82rem; font-weight: 600; color: var(--ink-600); letter-spacing: 0.002em; }
.field .hint { font-weight: 450; color: var(--slate-500); font-size: 0.76rem; }
.field[hidden] { display: none; }

.control {
  display: flex; align-items: center; height: 46px;
  background: var(--surface); border: 1px solid var(--line-strong); border-radius: var(--r-sm);
  transition: border-color var(--dur-1) var(--ease), box-shadow var(--dur-1) var(--ease);
  overflow: hidden;
}
.control:hover { border-color: var(--slate-400); }
.control:focus-within { border-color: var(--accent); box-shadow: 0 0 0 3.5px var(--ring); }
.control input, .control select {
  flex: 1; min-width: 0; height: 100%; border: none; outline: none; background: transparent;
  padding: 0 0.85rem; font-size: 0.97rem; font-weight: 500; color: var(--ink-900);
  font-variant-numeric: tabular-nums;
  appearance: textfield; -moz-appearance: textfield;
}
.control input::-webkit-outer-spin-button, .control input::-webkit-inner-spin-button { -webkit-appearance: none; }
.control input::placeholder { color: var(--slate-300); font-weight: 400; }
.control.prefix span, .control.suffix span {
  flex: none; color: var(--slate-400); font-weight: 550; font-size: 0.88rem; line-height: 1;
}
.control.prefix span { padding-left: 0.85rem; }
.control.prefix input { padding-left: 0.4rem; }
.control.suffix span { padding-right: 0.85rem; }
.control.suffix input { padding-right: 0.4rem; }
.control.select select { cursor: pointer; padding-right: 0.6rem; }
.form-note { font-size: 0.78rem; color: var(--slate-500); line-height: 1.55; }

/* ---------- segmented control ---------- */
.seg {
  display: inline-flex; gap: 3px; padding: 3px;
  background: #eef1f7; border-radius: var(--r-sm);
  border: 1px solid var(--line);
  max-width: 100%;
}
.seg-wrap { flex-wrap: wrap; }
.seg-btn {
  border: none; background: transparent; color: var(--slate-500);
  padding: 0.44rem 0.85rem; border-radius: 8px;
  font-size: 0.84rem; font-weight: 600; white-space: nowrap;
  transition: color var(--dur-1) var(--ease), background var(--dur-1) var(--ease), box-shadow var(--dur-1) var(--ease);
}
.seg-btn:hover { color: var(--ink-800); }
.seg-btn:focus-visible { outline: 2px solid var(--accent); outline-offset: -2px; }
.seg-btn.active {
  background: #fff; color: var(--ink-900);
  box-shadow: 0 1px 2px rgba(16, 24, 40, 0.1), 0 0 0 1px rgba(16, 24, 40, 0.04);
}
@media (max-width: 480px) {
  .seg { display: flex; flex-wrap: wrap; width: 100%; }
  .seg-btn { flex: 1 1 auto; min-width: 0; }
}

/* ---------- results ---------- */
.panel-results { display: flex; flex-direction: column; gap: 0.9rem; }
.result-hero {
  position: relative; overflow: hidden;
  background: linear-gradient(165deg, var(--ink-800), var(--ink-950));
  border-radius: var(--r-md); padding: 1.55rem 1.65rem 1.6rem;
  color: #fff;
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.07), var(--shadow-2);
}
.result-hero::after {
  content: ""; position: absolute; top: -60%; right: -20%;
  width: 340px; height: 260px;
  background: radial-gradient(50% 50% at 50% 50%, rgba(36, 86, 230, 0.22), transparent 70%);
  pointer-events: none;
}
.result-label {
  display: block; font-size: 0.72rem; font-weight: 650;
  letter-spacing: 0.09em; text-transform: uppercase; color: var(--slate-500);
  margin-bottom: 0.35rem;
}
.result-hero .result-label { color: #8fa2c9; }
.result-value {
  display: block; font-size: clamp(1.85rem, 4.4vw, 2.45rem);
  font-weight: 700; letter-spacing: -0.025em; line-height: 1.12;
  font-variant-numeric: tabular-nums;
}
.result-value.sm { font-size: clamp(1.12rem, 2.6vw, 1.35rem); letter-spacing: -0.015em; }
.result-value.updated { animation: tick var(--dur-3) var(--ease); }
@keyframes tick {
  0% { opacity: 0.4; transform: translateY(3px); }
  100% { opacity: 1; transform: none; }
}
.result-note { display: block; margin-top: 0.55rem; font-size: 0.85rem; color: #a5b3cf; line-height: 1.55; max-width: 46ch; }
.result-note.good { color: #5eead4; }
.result-note.warn { color: #fcd34d; }
.result-note:empty { display: none; }

.result-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.9rem; }
@media (max-width: 420px) { .result-grid { grid-template-columns: 1fr; } }
.result-card {
  background: var(--surface-2); border: 1px solid var(--line);
  border-radius: var(--r-md); padding: 1rem 1.1rem;
}
.result-card.wide { grid-column: 1 / -1; }
.result-card .result-label { margin-bottom: 0.25rem; }
.result-card .hint { text-transform: none; letter-spacing: 0; font-weight: 450; color: var(--slate-500); }
.result-card.positive { background: var(--mint-soft); border-color: #b9e7d8; }
.result-card.positive .result-value { color: var(--mint-deep); }
.result-card.positive .result-label { color: var(--mint-deep); opacity: 0.75; }
.result-card.negative { background: var(--rose-soft); border-color: #f3c3d0; }
.result-card.negative .result-value { color: var(--rose-deep); }
.result-card.negative .result-label { color: var(--rose-deep); opacity: 0.75; }
.formula-card code {
  display: block; margin-top: 0.25rem; font-size: 0.9rem; font-weight: 550;
  color: var(--ink-700); word-break: break-word;
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
}

/* ---------- mortgage breakdown: tonal scale, one warning hue ---------- */
.breakdown {
  display: flex; flex-direction: column; gap: 0.75rem;
  background: var(--surface-2); border: 1px solid var(--line);
  border-radius: var(--r-md); padding: 1rem 1.1rem;
}
.breakdown-bar {
  display: flex; height: 10px; border-radius: 999px; overflow: hidden;
  background: #eef1f6;
}
.breakdown-bar span { display: block; height: 100%; transition: width var(--dur-3) var(--ease); }
.bd-pi { background: var(--accent); }
.bd-tax { background: #7f9cf2; }
.bd-ins { background: #bccdf8; }
.bd-hoa { background: #94a3b8; }
.bd-pmi { background: var(--rose); }
.breakdown-legend {
  list-style: none; padding: 0; display: flex; flex-wrap: wrap; gap: 0.45rem 1.15rem;
  font-size: 0.8rem; color: var(--slate-500); font-weight: 500;
}
.breakdown-legend b { color: var(--ink-900); font-weight: 650; font-variant-numeric: tabular-nums; margin-left: 0.3rem; }
.breakdown-legend .dot { display: inline-block; width: 8px; height: 8px; border-radius: 50%; margin-right: 0.4rem; }

/* ---------- amortization table ---------- */
.amort {
  overflow-x: auto;
  background: var(--surface-2); border: 1px solid var(--line);
  border-radius: var(--r-md); padding: 1rem 1.1rem 0.6rem;
}
.amort h4 {
  font-size: 0.72rem; font-weight: 650; letter-spacing: 0.09em; text-transform: uppercase;
  margin-bottom: 0.6rem; color: var(--slate-500);
}
.amort table { width: 100%; border-collapse: collapse; font-size: 0.84rem; font-variant-numeric: tabular-nums; }
.amort th, .amort td { text-align: right; padding: 0.48rem 0.7rem; border-bottom: 1px solid var(--line); white-space: nowrap; }
.amort th:first-child, .amort td:first-child { text-align: left; padding-left: 0; }
.amort th:last-child, .amort td:last-child { padding-right: 0; }
.amort th {
  font-size: 0.68rem; text-transform: uppercase; letter-spacing: 0.07em;
  color: var(--slate-500); font-weight: 650;
}
.amort td { color: var(--ink-700); }
.amort tr:last-child td { border-bottom: none; }

/* ---------- explain ---------- */
.explain {
  border: 1px solid var(--line); border-radius: var(--r-md);
  background: var(--surface-2); overflow: hidden;
}
.explain summary {
  list-style: none; cursor: pointer; user-select: none;
  padding: 0.85rem 1.1rem; font-weight: 600; font-size: 0.86rem; color: var(--ink-600);
  display: flex; align-items: center; justify-content: space-between;
  transition: background var(--dur-1) var(--ease), color var(--dur-1) var(--ease);
}
.explain summary::-webkit-details-marker { display: none; }
.explain summary::after {
  content: "+"; font-size: 1.1rem; font-weight: 450; color: var(--slate-400);
  transition: transform var(--dur-2) var(--ease);
}
.explain[open] summary::after { transform: rotate(45deg); }
.explain summary:hover { background: #f2f5fa; color: var(--ink-900); }
.explain > div {
  padding: 0.15rem 1.1rem 1.05rem; font-size: 0.85rem; color: var(--slate-500);
  display: flex; flex-direction: column; gap: 0.55rem; line-height: 1.65;
  animation: fadeIn var(--dur-2) var(--ease);
}
@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }
.explain code {
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  background: var(--accent-soft); color: var(--accent-deep);
  padding: 0.08em 0.35em; border-radius: 5px; font-size: 0.92em;
}

/* ---------- unit converter ---------- */
.convert-row { display: grid; grid-template-columns: 1fr auto 1fr; gap: 0.7rem; align-items: end; }
@media (max-width: 480px) {
  .convert-row { grid-template-columns: 1fr; }
  .swap-btn { justify-self: center; transform: rotate(90deg); }
  .swap-btn:hover { transform: rotate(270deg); }
}
.swap-btn {
  width: 46px; height: 46px; flex: none;
  border: 1px solid var(--line-strong); border-radius: var(--r-sm);
  background: var(--surface); color: var(--slate-500);
  display: grid; place-items: center;
  transition: color var(--dur-2) var(--ease), border-color var(--dur-2) var(--ease), transform var(--dur-3) var(--ease);
}
.swap-btn svg { width: 18px; height: 18px; }
.swap-btn:hover { color: var(--accent); border-color: var(--accent); transform: rotate(180deg); }

/* ==========================================================================
   LEARN — editorial two-column, numbered
   ========================================================================== */
.section-learn { background: var(--surface); border-top: 1px solid var(--line); }
.learn-grid {
  display: grid; gap: 0.9rem;
  grid-template-columns: 1fr;
  counter-reset: learn;
}
@media (min-width: 720px) { .learn-grid { grid-template-columns: 1fr 1fr; } }
.learn-card {
  position: relative;
  background: var(--bg); border: 1px solid var(--line);
  border-radius: var(--r-md); padding: 1.5rem 1.5rem 1.55rem;
  transition: border-color var(--dur-2) var(--ease), box-shadow var(--dur-2) var(--ease);
}
.learn-card:hover { border-color: var(--line-strong); box-shadow: var(--shadow-1); }
.learn-card::before {
  counter-increment: learn;
  content: "0" counter(learn);
  display: block;
  font-size: 0.72rem; font-weight: 700; letter-spacing: 0.12em;
  color: var(--accent); margin-bottom: 0.75rem;
  font-variant-numeric: tabular-nums;
}
.learn-card h3 { font-size: 1rem; font-weight: 650; letter-spacing: -0.011em; margin-bottom: 0.5rem; }
.learn-card p { font-size: 0.88rem; color: var(--slate-500); line-height: 1.7; }
.learn-card code {
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  background: var(--accent-soft); color: var(--accent-deep);
  padding: 0.05em 0.3em; border-radius: 5px; font-size: 0.9em;
}

/* ==========================================================================
   FOOTER
   ========================================================================== */
.footer { background: var(--ink-950); color: var(--slate-400); padding: 3rem 0 2.4rem; }
.footer-top {
  display: flex; align-items: center; justify-content: space-between; gap: 1rem; flex-wrap: wrap;
  padding-bottom: 1.6rem; margin-bottom: 1.6rem;
  border-bottom: 1px solid rgba(255, 255, 255, 0.07);
}
.footer .brand-name { font-size: 0.98rem; }
.footer-links { display: flex; gap: 1.5rem; }
.footer-links a { text-decoration: none; font-size: 0.85rem; color: var(--slate-400); transition: color var(--dur-1) var(--ease); }
.footer-links a:hover { color: #fff; }
.footer-calcs {
  display: flex; flex-wrap: wrap; gap: 0.5rem 1.4rem;
  margin-bottom: 1.5rem;
}
.footer-calcs a {
  text-decoration: none; font-size: 0.82rem; color: var(--slate-400);
  transition: color var(--dur-1) var(--ease);
}
.footer-calcs a:hover { color: #fff; }
.footer-disclaimer { font-size: 0.82rem; line-height: 1.7; max-width: 70ch; margin-bottom: 0.9rem; color: var(--slate-400); }
.footer-copy { font-size: 0.76rem; color: var(--slate-500); }

/* ==========================================================================
   MOTION PREFERENCES
   ========================================================================== */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: 0.01ms !important; transition-duration: 0.01ms !important; }
  html { scroll-behavior: auto; }
}