:root {
  --bg: #edf2f6;
  --bg-2: #e6edf3;
  --panel: #0f1728;
  --panel-2: #17233a;
  --panel-3: #21314f;
  --surface: #ffffff;
  --surface-2: #f6f9fc;
  --surface-3: #eef3f8;
  --text: #142033;
  --text-soft: #516072;
  --text-inverse: #f5f8fd;
  --line: #d7e0ea;
  --line-strong: #bcc9d7;
  --shadow: 0 24px 48px rgba(18, 29, 43, 0.08);
  --shadow-soft: 0 10px 24px rgba(18, 29, 43, 0.06);
  --radius-xl: 24px;
  --radius-lg: 18px;
  --radius-md: 12px;
  --font-head: "IBM Plex Sans", "Noto Sans SC", sans-serif;
  --font-body: "IBM Plex Sans", "Noto Sans SC", sans-serif;
  --font-mono: "IBM Plex Mono", monospace;
  --blue: #256ef2;
  --purple: #6e56cf;
  --red: #d14343;
  --orange: #df8a1a;
  --green: #228a50;
  --cyan: #0c8ca3;
  --teal: #0b7f73;
  --indigo: #3754d6;
  --coral: #d96b45;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100vh;
  background:
    linear-gradient(rgba(255, 255, 255, 0.48) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255, 255, 255, 0.48) 1px, transparent 1px),
    linear-gradient(180deg, var(--bg) 0%, var(--bg-2) 100%);
  background-size: 32px 32px, 32px 32px, auto;
  color: var(--text);
  font-family: var(--font-body);
}

button,
input,
textarea {
  font: inherit;
}

input,
textarea {
  font-variant-numeric: tabular-nums;
}

.page-shell {
  width: min(1440px, calc(100vw - 32px));
  margin: 18px auto 40px;
}

.hero {
  padding: 24px 28px;
  border: 1px solid rgba(255, 255, 255, 0.5);
  border-radius: 28px;
  background:
    linear-gradient(140deg, rgba(15, 23, 40, 0.98), rgba(24, 36, 61, 0.95)),
    linear-gradient(180deg, rgba(37, 110, 242, 0.2), transparent);
  box-shadow: 0 28px 60px rgba(16, 27, 45, 0.14);
}

.hero-copy {
  max-width: 880px;
}

.eyebrow,
.panel-label,
.card-kicker,
.section-kicker {
  margin: 0;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  font-size: 0.76rem;
  font-weight: 700;
  color: #7eb0ff;
}

.hero h1,
.section-intro h2,
.formula-intro h2,
.card-head h2,
.cluster h3 {
  margin: 0;
  font-family: var(--font-head);
  letter-spacing: -0.02em;
}

.hero h1 {
  margin-top: 10px;
  color: var(--text-inverse);
  font-size: clamp(2.4rem, 4vw, 4rem);
  line-height: 1;
}

.lead {
  margin: 14px 0 0;
  max-width: 64ch;
  color: rgba(245, 248, 253, 0.78);
  font-size: 1rem;
  line-height: 1.72;
}

.tabbar {
  display: inline-flex;
  gap: 8px;
  margin: 20px 0 18px;
  padding: 6px;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: rgba(255, 255, 255, 0.88);
  box-shadow: var(--shadow-soft);
}

.tab-button {
  border: 0;
  border-radius: 10px;
  padding: 11px 16px;
  background: transparent;
  color: var(--text-soft);
  font-weight: 600;
  cursor: pointer;
  transition: background 0.2s ease, color 0.2s ease, transform 0.2s ease;
}

.tab-button:hover {
  color: var(--text);
  background: var(--surface-3);
}

.tab-button.is-active {
  background: var(--panel);
  color: var(--text-inverse);
}

.content-panel {
  animation: fade-slide 0.18s ease;
}

@keyframes fade-slide {
  from {
    opacity: 0;
    transform: translateY(6px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.section-intro,
.formula-intro {
  display: flex;
  align-items: end;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 18px;
  padding: 0 2px;
}

.section-intro h2,
.formula-intro h2 {
  margin-top: 6px;
  font-size: 1.7rem;
}

.section-intro p:last-child,
.formula-intro p:last-child {
  max-width: 62ch;
  margin: 0;
  color: var(--text-soft);
  line-height: 1.65;
}

.cards-grid {
  display: grid;
  grid-template-columns: repeat(12, minmax(0, 1fr));
  gap: 16px;
}

.tool-card {
  grid-column: span 6;
  min-width: 0;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: var(--radius-xl);
  background: var(--surface);
  box-shadow: var(--shadow-soft);
}

.tool-card.wide {
  grid-column: span 12;
}

.card-stripe {
  height: 4px;
  background: var(--accent);
}

.tool-card.accent-blue {
  --accent: var(--blue);
  --accent-rgb: 37, 110, 242;
}

.tool-card.accent-purple {
  --accent: var(--purple);
  --accent-rgb: 110, 86, 207;
}

.tool-card.accent-red {
  --accent: var(--red);
  --accent-rgb: 209, 67, 67;
}

.tool-card.accent-orange {
  --accent: var(--orange);
  --accent-rgb: 223, 138, 26;
}

.tool-card.accent-green {
  --accent: var(--green);
  --accent-rgb: 34, 138, 80;
}

.tool-card.accent-cyan {
  --accent: var(--cyan);
  --accent-rgb: 12, 140, 163;
}

.tool-card.accent-teal {
  --accent: var(--teal);
  --accent-rgb: 11, 127, 115;
}

.tool-card.accent-indigo {
  --accent: var(--indigo);
  --accent-rgb: 55, 84, 214;
}

.tool-card.accent-coral {
  --accent: var(--coral);
  --accent-rgb: 217, 107, 69;
}

.card-head {
  padding: 18px 20px 12px;
  background: linear-gradient(180deg, rgba(var(--accent-rgb), 0.07), rgba(255, 255, 255, 0) 92%);
}

.card-kicker {
  margin-bottom: 8px;
  color: var(--accent);
}

.card-head h2 {
  font-size: 1.32rem;
}

.card-head p:last-child {
  margin: 8px 0 0;
  color: var(--text-soft);
  line-height: 1.58;
  font-size: 0.95rem;
}

.field-grid,
.cluster-grid {
  padding: 0 20px 20px;
}

.field-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
}

.field,
.field-wide {
  display: flex;
  flex-direction: column;
  gap: 8px;
  min-width: 0;
}

.field-wide {
  grid-column: span 2;
}

.field span {
  color: var(--text-soft);
  font-size: 0.85rem;
  font-weight: 600;
}

.calc-input,
.result-input,
.result-area {
  width: 100%;
  min-width: 0;
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
  padding: 12px 13px;
  background: var(--surface-2);
  color: var(--text);
  font-family: var(--font-mono);
  font-size: 0.95rem;
  transition: border-color 0.18s ease, box-shadow 0.18s ease, background 0.18s ease;
}

.calc-input:hover,
.result-area:hover {
  border-color: var(--line-strong);
}

.calc-input:focus,
.result-area:focus {
  outline: none;
  border-color: var(--accent, var(--blue));
  box-shadow: 0 0 0 4px rgba(var(--accent-rgb, 37, 110, 242), 0.12);
  background: #fff;
}

.result-input,
.result-area {
  background: rgba(var(--accent-rgb, 20, 32, 51), 0.06);
  color: var(--accent, var(--text));
  font-weight: 600;
}

.result-area {
  min-height: 92px;
  resize: vertical;
  line-height: 1.6;
}

.cluster-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
}

.cluster {
  min-width: 0;
  padding: 16px;
  border: 1px solid var(--line);
  border-radius: 18px;
  background: var(--surface-2);
}

.cluster h3 {
  margin-bottom: 12px;
  font-size: 1rem;
}

.cluster .field-grid {
  padding: 0;
  grid-template-columns: 1fr;
}

.formula-list {
  display: grid;
  gap: 12px;
}

.formula-card {
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 18px;
  background: var(--surface);
  box-shadow: var(--shadow-soft);
}

.formula-card summary {
  list-style: none;
  cursor: pointer;
  padding: 16px 18px;
  background: var(--surface-2);
  font-family: var(--font-head);
  font-size: 1.02rem;
  font-weight: 600;
}

.formula-card summary::-webkit-details-marker {
  display: none;
}

.formula-body {
  padding: 18px;
}

.formula-body p {
  margin: 0 0 14px;
  color: var(--text-soft);
  line-height: 1.7;
}

.formula-body pre {
  margin: 0;
  overflow-x: auto;
  border-radius: 14px;
  border: 1px solid rgba(126, 176, 255, 0.12);
  background: #0f1728;
  color: #89b4ff;
  padding: 14px;
  font-family: var(--font-mono);
  font-size: 0.9rem;
  line-height: 1.7;
}

.site-footer {
  display: flex;
  align-items: center;
  justify-content: center;
  margin-top: 18px;
  padding: 14px 4px 0;
  border-top: 1px solid rgba(20, 32, 51, 0.08);
  color: var(--text-soft);
  font-size: 0.9rem;
}

.site-footer p {
  margin: 0;
}

code {
  font-family: var(--font-mono);
  font-size: 0.9em;
}

@media (max-width: 1180px) {
  .hero {
    grid-template-columns: 1fr;
  }

  .tool-card {
    grid-column: span 12;
  }

  .tool-card.wide {
    grid-column: span 12;
  }

  .cluster-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 760px) {
  .page-shell {
    width: min(100vw - 16px, 100%);
    margin: 8px auto 28px;
  }

  .hero {
    padding: 18px;
    border-radius: 20px;
  }

  .hero h1 {
    font-size: 2.25rem;
  }

  .tabbar {
    display: flex;
    width: 100%;
  }

  .tab-button {
    flex: 1;
  }

  .section-intro,
  .formula-intro {
    flex-direction: column;
    align-items: start;
  }

  .field-grid {
    grid-template-columns: 1fr;
  }

  .field-wide {
    grid-column: auto;
  }

  .site-footer {
    justify-content: center;
  }

}