/* ============================================================
   OctaCalc — Global Stylesheet
   Aesthetic: Modern SaaS / soft dark — grey + ink blue
   Font: DM Mono + Plus Jakarta Sans
   ============================================================ */

@import url('https://fonts.googleapis.com/css2?family=DM+Mono:wght@300;400;500&family=Plus+Jakarta+Sans:wght@300;400;500;600&display=swap');

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

/* ── Design Tokens ───────────────────────────────────────── */
:root {
  --bg:          #f0f2f7;
  --bg-deep:     #e4e8f2;
  --surface:     #ffffff;
  --surface-alt: #f7f8fc;
  --border:      #dde1ed;
  --border-dk:   #b8bfd4;
  --text:        #16181f;
  --text-mid:    #4a5068;
  --text-soft:   #8890aa;
  --accent:      #3d6af0;
  --accent-dk:   #2a52cc;
  --accent-bg:   #eef2fe;
  --accent-glow: rgba(61,106,240,.14);
  --result-bg:   #1a2040;
  --result-mid:  #243060;
  --result-fg:   #eef2fe;
  --result-unit: #7da4ff;
  --mono:        'DM Mono', 'Courier New', monospace;
  --sans:        'Plus Jakarta Sans', system-ui, sans-serif;
  --radius-sm:   8px;
  --radius:      14px;
  --radius-lg:   20px;
  --shadow-sm:   0 1px 3px rgba(30,40,90,.07), 0 2px 8px rgba(30,40,90,.05);
  --shadow:      0 2px 8px rgba(30,40,90,.08), 0 8px 28px rgba(30,40,90,.08);
  --shadow-card: 0 4px 16px rgba(30,40,90,.09), 0 1px 3px rgba(30,40,90,.06);
}

/* ── Base ────────────────────────────────────────────────── */
html { font-size: 16px; scroll-behavior: smooth; }

body {
  font-family: var(--sans);
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ── Site Header ─────────────────────────────────────────── */
.site-header {
  background: rgba(240,242,247,.82);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
  padding: 0 1.5rem;
  position: sticky;
  top: 0;
  z-index: 100;
}

.site-header-inner {
  max-width: 880px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  gap: 1.5rem;
  height: 56px;
}

.site-logo {
  font-family: var(--mono);
  font-size: 1rem;
  font-weight: 500;
  letter-spacing: .05em;
  color: var(--text);
  text-decoration: none;
  flex-shrink: 0;
}

.site-logo span { color: var(--accent); }

.header-tagline {
  font-family: var(--sans);
  font-size: .75rem;
  font-weight: 400;
  color: var(--text-soft);
  border-left: 1px solid var(--border);
  padding-left: 1.5rem;
}

/* ── Main Layout ─────────────────────────────────────────── */
main {
  flex: 1;
  max-width: 880px;
  margin: 0 auto;
  padding: 3rem 1.5rem 4.5rem;
  width: 100%;
}

/* ── Homepage ────────────────────────────────────────────── */
.home-hero {
  margin-bottom: 2.5rem;
  padding-bottom: 2.5rem;
  border-bottom: 1px solid var(--border);
}

.home-hero h1 {
  font-family: var(--mono);
  font-size: clamp(2.2rem, 5vw, 3.2rem);
  font-weight: 300;
  letter-spacing: -.02em;
  line-height: 1.1;
  margin-bottom: .9rem;
}

.home-hero h1 em {
  color: var(--accent);
  font-style: normal;
}

.home-hero p {
  font-size: 1.05rem;
  font-weight: 400;
  color: var(--text-mid);
  max-width: 480px;
}

/* Tool Grid — individual cards with gap */
.tool-grid {
  display: grid;
  gap: .75rem;
}

.tool-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  display: flex;
  align-items: center;
  gap: 1.1rem;
  text-decoration: none;
  color: inherit;
  box-shadow: var(--shadow-sm);
  transition: box-shadow .2s, border-color .2s, transform .15s;
}

.tool-card:hover {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-glow), var(--shadow);
  transform: translateY(-1px);
}

.tool-card:hover .tool-card-arrow { color: var(--accent); }

.tool-card-icon {
  width: 40px;
  height: 40px;
  border-radius: var(--radius-sm);
  background: var(--accent-bg);
  border: 1px solid rgba(61,106,240,.18);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  font-family: var(--mono);
  font-size: .68rem;
  font-weight: 500;
  color: var(--accent);
  letter-spacing: .03em;
}

.tool-card-content { flex: 1; }

.tool-card-title {
  font-family: var(--sans);
  font-size: .95rem;
  font-weight: 600;
  margin-bottom: .2rem;
  color: var(--text);
}

.tool-card-desc {
  font-size: .82rem;
  color: var(--text-soft);
  font-weight: 400;
}

.tool-card-arrow {
  color: var(--border-dk);
  font-size: 1rem;
  transition: color .2s;
  flex-shrink: 0;
}

/* ── Tool Page ───────────────────────────────────────────── */
.tool-breadcrumb {
  font-family: var(--mono);
  font-size: .73rem;
  color: var(--text-soft);
  margin-bottom: 2rem;
  letter-spacing: .03em;
}

.tool-breadcrumb a { color: var(--accent); text-decoration: none; }
.tool-breadcrumb a:hover { text-decoration: underline; }

.tool-header { margin-bottom: 2.5rem; }

.tool-header h1 {
  font-family: var(--mono);
  font-size: clamp(1.45rem, 3.5vw, 2rem);
  font-weight: 400;
  letter-spacing: -.02em;
  line-height: 1.2;
  margin-bottom: .65rem;
}

.tool-header p {
  font-size: 1rem;
  color: var(--text-mid);
  max-width: 520px;
  font-weight: 400;
}

/* ── Calculator Card ─────────────────────────────────────── */
.calc-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow-card);
  margin-bottom: 2.5rem;
}

.calc-card-inner {
  padding: 2rem 2rem 2rem;
}

/* Field Groups */
.field-group {
  display: grid;
  gap: 1.1rem;
  margin-bottom: 1.5rem;
}

.field {
  display: flex;
  flex-direction: column;
  gap: .45rem;
}

label {
  font-family: var(--sans);
  font-size: .78rem;
  font-weight: 600;
  letter-spacing: .03em;
  color: var(--text-mid);
}

label .unit {
  font-weight: 400;
  color: var(--text-soft);
  letter-spacing: 0;
  margin-left: .2rem;
}

input[type="number"],
input[type="text"],
select {
  width: 100%;
  padding: .8rem 1rem;
  font-family: var(--mono);
  font-size: 1.08rem;
  font-weight: 400;
  color: var(--text);
  background: var(--surface-alt);
  border: 1.5px solid var(--border);
  border-radius: var(--radius-sm);
  outline: none;
  transition: border-color .18s, box-shadow .18s, background .18s;
  -moz-appearance: textfield;
}

input[type="number"]::-webkit-outer-spin-button,
input[type="number"]::-webkit-inner-spin-button { -webkit-appearance: none; }

input:focus {
  border-color: var(--accent);
  background: var(--surface);
  box-shadow: 0 0 0 3px var(--accent-glow);
}

input.error-field { border-color: #e05555; }

/* Input hint */
.input-hint {
  font-family: var(--sans);
  font-size: .75rem;
  font-weight: 400;
  color: var(--text-soft);
  margin-top: -.1rem;
  padding: .5rem .75rem;
  background: var(--accent-bg);
  border-radius: var(--radius-sm);
  border: 1px solid rgba(61,106,240,.15);
}

/* Calculate Button */
.btn-calc {
  width: 100%;
  padding: .9rem 1rem;
  font-family: var(--sans);
  font-size: .9rem;
  font-weight: 600;
  letter-spacing: .02em;
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: background .18s, box-shadow .18s, transform .12s;
  box-shadow: 0 2px 8px rgba(61,106,240,.3);
}

.btn-calc:hover {
  background: var(--accent-dk);
  box-shadow: 0 4px 14px rgba(61,106,240,.38);
}

.btn-calc:active { transform: translateY(1px); box-shadow: none; }

/* Result Panel */
.result-panel {
  display: none;
  background: var(--result-bg);
  color: var(--result-fg);
  padding: 1.75rem 2rem;
  position: relative;
  overflow: hidden;
}

/* Subtle decorative glow blob behind result */
.result-panel::before {
  content: '';
  position: absolute;
  top: -40px;
  right: -40px;
  width: 180px;
  height: 180px;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(61,106,240,.25) 0%, transparent 70%);
  pointer-events: none;
}

.result-panel.visible { display: block; }

.result-label {
  font-family: var(--sans);
  font-size: .7rem;
  font-weight: 600;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--result-unit);
  opacity: .7;
  margin-bottom: .5rem;
}

.result-value {
  font-family: var(--mono);
  font-size: clamp(2rem, 6vw, 3rem);
  font-weight: 300;
  line-height: 1;
  margin-bottom: .5rem;
  position: relative;
}

.result-value .result-unit {
  font-size: .42em;
  color: var(--result-unit);
  margin-left: .3em;
  font-weight: 400;
}

.result-note {
  font-family: var(--mono);
  font-size: .73rem;
  color: rgba(180,195,255,.55);
  position: relative;
}

/* Error panel */
.error-panel {
  display: none;
  background: #fdf0f0;
  border-top: 2px solid #e05555;
  padding: 1.1rem 2rem;
  font-family: var(--sans);
  font-size: .85rem;
  font-weight: 500;
  color: #c94444;
}

.error-panel.visible { display: block; }

/* ── Content Sections ────────────────────────────────────── */
.content-section {
  margin-bottom: 2.25rem;
}

.content-section h2 {
  font-family: var(--sans);
  font-size: .72rem;
  font-weight: 700;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--text-soft);
  margin-bottom: .9rem;
  padding-bottom: .5rem;
  border-bottom: 1px solid var(--border);
}

.content-section p {
  font-size: .95rem;
  font-weight: 400;
  color: var(--text-mid);
  margin-bottom: .75rem;
  max-width: 580px;
}

/* Formula block */
.formula-block {
  background: var(--surface);
  border: 1.5px solid var(--border);
  border-left: 3px solid var(--accent);
  border-radius: var(--radius-sm);
  padding: .85rem 1.25rem;
  font-family: var(--mono);
  font-size: 1rem;
  color: var(--text);
  margin: .6rem 0;
  display: inline-block;
  min-width: 200px;
  box-shadow: var(--shadow-sm);
}

/* Example block */
.example-block {
  background: var(--surface);
  border: 1.5px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 1.25rem 1.5rem;
  font-family: var(--mono);
  font-size: .84rem;
  color: var(--text-mid);
  line-height: 1.95;
  box-shadow: var(--shadow-sm);
}

.example-block strong {
  color: var(--text);
  font-weight: 500;
}

.example-block .ex-result {
  color: var(--accent);
  font-weight: 500;
}

/* ── Related Tools ───────────────────────────────────────── */
.related-tools {
  margin-top: 2.75rem;
  padding-top: 2rem;
  border-top: 1px solid var(--border);
}

.related-tools h2 {
  font-family: var(--sans);
  font-size: .72rem;
  font-weight: 700;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--text-soft);
  margin-bottom: .9rem;
}

.related-list {
  display: flex;
  flex-wrap: wrap;
  gap: .55rem;
}

.related-link {
  font-family: var(--sans);
  font-size: .8rem;
  font-weight: 500;
  padding: .45rem 1rem;
  border: 1.5px solid var(--border);
  border-radius: 100px;
  color: var(--text-mid);
  text-decoration: none;
  background: var(--surface);
  transition: border-color .18s, color .18s, background .18s, box-shadow .18s;
}

.related-link:hover {
  border-color: var(--accent);
  color: var(--accent);
  background: var(--accent-bg);
  box-shadow: 0 0 0 3px var(--accent-glow);
}

/* ── Site Footer ─────────────────────────────────────────── */
footer {
  border-top: 1px solid var(--border);
  padding: 1.5rem;
  text-align: center;
  font-family: var(--sans);
  font-size: .75rem;
  font-weight: 400;
  color: var(--text-soft);
}

footer a { color: var(--accent); text-decoration: none; }
footer a:hover { text-decoration: underline; }

/* ── Responsive ──────────────────────────────────────────── */
@media (min-width: 600px) {
  .field-group.two-col { grid-template-columns: 1fr 1fr; }
  .field-group.three-col { grid-template-columns: 1fr 1fr 1fr; }
}

@media (max-width: 480px) {
  main { padding: 2rem 1rem 3.5rem; }
  .calc-card-inner { padding: 1.25rem; }
  .result-panel { padding: 1.35rem 1.25rem; }
  .error-panel { padding: 1rem 1.25rem; }
}