*,
*::before,
*::after {
  box-sizing: border-box;
}

html,
body,
h1,
h2,
h3,
h4,
p,
ul,
ol,
figure,
blockquote {
  margin: 0;
}

:root {
  color-scheme: light;

  /* typography */
  --sans: "DM Sans", sans-serif;
  --serif: "Playfair Display", serif;
  --mono: "IBM Plex Mono", monospace;

  /* core palette */
  --color-ink: #111827;
  --color-paper: #f5f0e8;
  --color-surface: #ffffff;
  --color-surface-alt: #faf6ef;
  --color-border: #c9bda7;
  --color-border-soft: #ded6c8;

  /* text */
  --color-text-muted: #4b5563;
  --color-text-soft: #6b7280;
  --color-text-inverse: #f8fafc;
  --color-text-inverse-muted: #dbe3ec;
  --color-text-inverse-soft: #b7c2cd;

  /* semantic / accent */
  --color-accent: #a82f25;
  --color-accent-hover: #8f281f;
  --color-accent-soft: rgba(168, 47, 37, 0.08);
  --color-accent-on-dark: #ff9b8f;
  --color-success: #1f6a42;

  --color-info-50: #eff6ff;
  --color-info-700: #1d4ed8;
  --color-warning-50: #fffbeb;
  --color-warning-700: #92400e;

  /* dark surfaces */
  --color-dark: #0f1117;
  --color-dark-surface: #161b22;
  --color-dark-border: #2b3440;

  /* elevation + focus */
  --shadow-sm: 0 2px 6px rgba(17, 24, 39, 0.08);
  --shadow-hover: 0 6px 18px rgba(17, 24, 39, 0.12);
  --shadow-card:
    0 20px 60px rgba(17, 24, 39, 0.14), 0 2px 8px rgba(17, 24, 39, 0.06);

  --focus-ring-color: rgba(168, 47, 37, 0.28);
  --focus-ring: 0 0 0 3px var(--focus-ring-color);

  /* legacy aliases */
  --ink: var(--color-ink);
  --paper: var(--color-paper);
  --rule: var(--color-border);
  --border: var(--color-border);
  --text-muted: var(--color-text-muted);
  --accent: var(--color-accent);
  --green: var(--color-success);

  /* header / footer tokens */
  --ue-primary: #4338ca;
  --ue-primary-hover: #3730a3;
  --ue-primary-soft: #eef2ff;
  --ue-primary-mid: #818cf8;

  --ue-text: var(--color-ink);
  --ue-text-muted: var(--color-text-muted);
  --ue-text-dim: #6b7280;

  --ue-surface: var(--color-surface);
  --ue-border: var(--color-border);
  --ue-border-soft: var(--color-border-soft);

  --ue-mono: var(--mono);
  --ue-serif: var(--serif);
  --ue-sans: var(--sans);

  --ue-accent-border: #c7d2fe;

  --ue-hdr-bg: var(--color-surface);
  --ue-hdr-border: var(--color-border-soft);
  --ue-hdr-muted: #4b5563;
  --ue-hdr-hover-bg: var(--ue-primary-soft);

  --ue-ftr-bg: var(--color-dark);
  --ue-ftr-surface: var(--color-dark-surface);
  --ue-ftr-border: var(--color-dark-border);
  --ue-ftr-text: var(--color-text-inverse);
  --ue-ftr-muted: var(--color-text-inverse-soft);
  --ue-ftr-accent: var(--ue-primary-mid);

  /* aliases for inline semantic tones */
  --info-50: var(--color-info-50);
  --info-700: var(--color-info-700);
  --warning-50: var(--color-warning-50);
  --warning-700: var(--color-warning-700);
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: var(--sans);
  background: var(--paper);
  color: var(--ink);
  min-height: 100vh;
  overflow-x: hidden;
  line-height: 1.5;
}

body::before {
  content: "";
  position: fixed;
  inset: 0;
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 200 200' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.85' numOctaves='4' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)' opacity='0.04'/%3E%3C/svg%3E");
  pointer-events: none;
  z-index: 999;
  opacity: 0.35;
}

img,
svg {
  display: block;
  max-width: 100%;
}

a {
  color: inherit;
}

button,
input,
select,
textarea {
  font: inherit;
}

.skip-link {
  position: absolute;
  top: 8px;
  left: 8px;
  z-index: 2000;
  padding: 10px 14px;
  background: var(--color-surface);
  color: var(--ink);
  border: 2px solid var(--accent);
  border-radius: 8px;
  text-decoration: none;
  transform: translateY(-140%);
  transition: transform 0.2s ease;
}

.skip-link:focus {
  transform: translateY(0);
}

:where(
  a[href],
  button,
  input,
  select,
  textarea,
  [role="button"],
  [role="tab"]
):focus-visible {
  outline: 3px solid var(--accent);
  outline-offset: 3px;
}

.swap-btn:focus,
.field-group input:focus,
.field-group select:focus {
  outline: none;
}

.swap-btn {
  width: 44px;
  height: 44px;
  min-width: 44px;
  min-height: 44px;
  border-radius: 50%;
  border: 1px solid var(--border);
  background: var(--rule);
  color: var(--text-muted);
  cursor: pointer;
  font-size: 18px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  transition:
    transform 0.2s,
    border-color 0.2s,
    background 0.2s,
    color 0.2s,
    box-shadow 0.2s;
  flex-shrink: 0;
  box-shadow: var(--shadow-sm);
  text-decoration: none;
}

.swap-btn:hover {
  border-color: var(--accent);
  color: var(--accent);
  transform: rotate(180deg);
  background: var(--color-surface);
  box-shadow: var(--shadow-hover);
}

.swap-btn:focus-visible {
  box-shadow: var(--focus-ring);
}

.masthead-top .nav-link,
.masthead-top .btn,
.masthead-top .menu-toggle,
.tab-btn,
.copy-result,
.swap-btn {
  min-height: 44px;
}
.breadcrumbs {
  padding: 10px 50px;
}

.breadcrumbs ol {
  list-style: none;
  padding: 0;
  margin: 0;
  display: flex;
  align-items: center;
  flex-wrap: wrap;
}

.breadcrumbs li {
  display: flex;
  align-items: center;
  font-family: var(--mono);
  font-size: 16px;
  letter-spacing: 0.06em;
}

/* separator */
.breadcrumbs li + li::before {
  content: "/";
  margin: 0 10px;
  color: var(--color-border);
  user-select: none;
}

.breadcrumbs a {
  color: var(--color-text-muted);
  text-decoration: none;
  padding: 2px 4px;
  border-radius: 3px;
  transition:
    color 0.15s,
    background 0.15s;
}

.breadcrumbs a:hover {
  color: var(--color-accent);
  background: var(--color-accent-soft);
}

.breadcrumbs a:focus-visible {
  outline: none;
  box-shadow: var(--focus-ring);
}

/* current page */
.breadcrumbs li[aria-current="page"] {
  color: var(--color-ink);
  font-weight: 600;
}
.hero {
  background: var(--color-dark);
  color: var(--color-text-inverse);
  padding: 28px 40px 36px;
  position: relative;
  overflow: hidden;
}

.hero-inner {
  max-width: 860px;
  margin: 0 auto;
  position: relative;
  z-index: 1;
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 24px;
  align-items: center;
}

.hero-tag {
  display: inline-block;
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--color-accent-on-dark);
  border: 1px solid var(--color-accent-on-dark);
  padding: 3px 8px;
  margin-bottom: 10px;
}

h1 {
  font-family: var(--serif);
  font-size: clamp(22px, 3.5vw, 32px);
  font-weight: 900;
  line-height: 1.1;
  letter-spacing: -0.02em;
  margin-bottom: 8px;
}

h1 em {
  font-style: italic;
  color: var(--accent);
}

.hero-sub {
  font-size: 13px;
  line-height: 1.6;
  color: var(--color-text-inverse-muted);
  max-width: 480px;
  font-weight: 400;
}

.hero-facts {
  display: flex;
  flex-direction: column;
  gap: 6px;
  flex-shrink: 0;
}

.hero-fact {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.06em;
  color: var(--color-text-inverse-soft);
  display: flex;
  align-items: center;
  gap: 8px;
}

.hero-fact::before {
  content: "";
  width: 4px;
  height: 4px;
  border-radius: 50%;
  background: var(--color-accent-on-dark);
  flex-shrink: 0;
}

.converter-wrap {
  max-width: 860px;
  margin: 0 auto;
  padding: 0 40px;
  margin-top: -1px;
  position: relative;
  z-index: 10;
}

.converter-card {
  background: var(--color-surface);
  border: 1px solid var(--rule);
  box-shadow: var(--shadow-card);
  border-radius: 2px;
  overflow: hidden;
  animation: fadeUp 0.35s ease both;
}

.converter-tabs {
  display: flex;
  border-bottom: 1px solid var(--rule);
  background: var(--paper);
}

.tab-btn {
  font-family: var(--mono);
  font-size: 12px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  padding: 14px 22px;
  background: none;
  border: none;
  cursor: pointer;
  color: var(--color-text-muted);
  border-bottom: 2px solid transparent;
  margin-bottom: -1px;
  transition:
    color 0.2s,
    background 0.2s,
    border-color 0.2s;
}

.tab-btn.active {
  border-bottom-color: var(--accent);
  color: var(--accent);
}

.tab-btn:hover {
  color: var(--ink);
  background: rgba(17, 24, 39, 0.04);
}

.tab-panel {
  display: block;
  padding: 40px 40px 32px;
}

.conv-row {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 16px;
  margin-bottom: 0;
  align-items: center;
}

.field-group label {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  display: block;
  margin-bottom: 8px;
  color: var(--color-text-muted);
}

.field-group input,
.field-group select {
  width: 100%;
  font-family: var(--mono);
  font-size: 44px;
  font-weight: 600;
  color: var(--ink);
  background: var(--color-surface-alt);
  border: 2px solid var(--rule);
  border-radius: 2px;
  padding: 18px 20px;
  transition:
    border-color 0.2s,
    box-shadow 0.2s,
    background 0.2s;
  line-height: 1;
}

.field-group input::placeholder {
  color: var(--color-text-soft);
  opacity: 1;
}

.field-group input:focus,
.field-group select:focus {
  border-color: var(--accent);
  box-shadow: var(--focus-ring);
}

.field-group input.result-field {
  background: var(--color-dark);
  color: var(--color-text-inverse);
  border-color: var(--color-dark);
  cursor: default;
}

.field-group .unit-hint {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--color-text-muted);
  margin-top: 6px;
  display: block;
}

.result-strip {
  margin-top: 16px;
  background: var(--color-dark);
  border-radius: 2px;
  padding: 18px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  min-height: 64px;
}

.result-eq {
  font-family: var(--mono);
  font-size: 18px;
  color: var(--color-text-inverse-muted);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.result-eq strong {
  color: var(--color-text-inverse);
  font-size: 22px;
  font-weight: 600;
}

.result-eq .result-unit {
  font-size: 14px;
  color: var(--color-text-inverse-soft);
  margin-left: 4px;
}

.formula-strip {
  background: var(--paper);
  border: 1px solid var(--rule);
  border-top: none;
  border-radius: 0 0 2px 2px;
  padding: 12px 18px;
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 0;
  margin-top: 0;
}

.formula-strip .label {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--color-text-muted);
  white-space: nowrap;
}

.formula-strip .formula {
  font-family: var(--mono);
  font-size: 13px;
  font-weight: 600;
  color: var(--green);
}

.copy-result {
  margin-left: auto;
  font-family: var(--mono);
  font-size: 11px;
  background: transparent;
  border: 1px solid rgba(248, 250, 252, 0.35);
  border-radius: 2px;
  padding: 6px 12px;
  cursor: pointer;
  color: var(--color-text-inverse);
  transition:
    background 0.2s,
    color 0.2s,
    border-color 0.2s;
  white-space: nowrap;
}

.copy-result:hover {
  border-color: var(--color-text-inverse);
  background: rgba(248, 250, 252, 0.06);
}

.copy-result.copied {
  border-color: #7ee2a8;
  color: #7ee2a8;
}

.section {
  max-width: 860px;
  margin: 0 auto;
  padding: 64px 40px;
}

.section-label {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--accent);
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 16px;
}

.section-label::after {
  content: "";
  flex: 1;
  height: 1px;
  background: var(--rule);
}

h2 {
  font-family: var(--serif);
  font-size: clamp(24px, 4vw, 40px);
  font-weight: 700;
  line-height: 1.15;
  margin-bottom: 12px;
}

.section-intro {
  font-size: 16px;
  line-height: 1.65;
  color: var(--color-text-muted);
  max-width: 60ch;
  margin-bottom: 36px;
}
/* ── Table wrap ── */
.table-wrap {
  overflow-x: auto;
  border-radius: 8px;
  border: 1px solid var(--color-border);
  box-shadow: var(--shadow-sm);
}
table caption {
  caption-side: top;
  text-align: left;
  padding: 0 0 18px;
  margin-bottom: 14px;
  font-family: var(--serif);
  font-size: clamp(22px, 2.8vw, 30px);
  line-height: 1.15;
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--color-ink);
  position: relative;
}

table caption::after {
  content: "";
  display: block;
  width: 100%;
  height: 1px;
  margin-top: 14px;
  background: var(--rule);
}
table {
  width: 100%;
  border-collapse: collapse;
}
caption {
  caption-side: top;
  padding: 0.75rem 1rem;
  font-size: 14px;
  font-weight: 700;
  color: var(--color-dark);
  text-align: left;
  letter-spacing: 0.01em;
  border-bottom: 0.5px solid var(--color-border);
  margin-bottom: 0.5rem;
}
/* ── Header ── */
thead tr {
  background: var(--color-ink);
}

thead th {
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.13em;
  text-transform: uppercase;
  padding: 14px 20px;
  text-align: left;
  font-weight: 600;
  color: #e5e7eb;
  border-bottom: 2px solid var(--accent);
}

thead th:first-child {
  border-radius: 7px 0 0 0;
}
thead th:last-child {
  border-radius: 0 7px 0 0;
}

/* ── Body rows ── */
tbody tr {
  border-bottom: 1px solid var(--color-border);
  transition:
    background 0.18s ease,
    transform 0.15s ease;
  background: var(--color-surface);
}

tbody tr:last-child {
  border-bottom: none;
}

/* Subtle stripe */
tbody tr:nth-child(even) {
  background: #faf7f3;
}

tbody tr:hover {
  background: var(--color-accent-soft);
}

/* ── Cells ── */
tbody td {
  padding: 14px 20px;
  font-size: 14px;
  line-height: 1.5;
  color: var(--color-ink);
  vertical-align: middle;
}

/* Col 1 — mono key */
tbody td:first-child {
  font-family: var(--mono);
  font-size: 13px;
  font-weight: 600;
  color: var(--color-ink);
  white-space: nowrap;
}

/* Col 2 — muted description */
tbody td:nth-child(2) {
  color: var(--color-text-soft);
  font-size: 13px;
  line-height: 1.6;
}

/* Col 3 — green value */
tbody td:last-child {
  font-family: var(--mono);
  font-size: 13px;
  font-weight: 600;
  color: var(--green);
  white-space: nowrap;
}

.full-rule {
  border: none;
  border-top: 1px solid var(--rule);
  max-width: 860px;
  margin: 0 auto;
}

.explain-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 32px;
}

.explain-card {
  border: 1px solid var(--rule);
  padding: 28px;
  background: var(--color-surface);
  border-radius: 2px;
}

.explain-card h3 {
  font-family: var(--serif);
  font-size: 20px;
  font-weight: 700;
  margin-bottom: 12px;
}

.explain-card p {
  font-size: 15px;
  line-height: 1.65;
  color: var(--color-text-muted);
}

.explain-card .big-formula {
  font-family: var(--mono);
  font-size: 22px;
  font-weight: 600;
  color: var(--accent);
  margin: 16px 0 8px;
  background: var(--paper);
  padding: 12px 16px;
  display: inline-block;
  border-left: 3px solid var(--accent);
}

.step {
  display: flex;
  gap: 16px;
  margin-bottom: 20px;
}

.step-num {
  width: 32px;
  height: 32px;
  border-radius: 50%;
  background: var(--ink);
  color: var(--color-text-inverse);
  font-family: var(--mono);
  font-size: 13px;
  font-weight: 600;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.step-body h4 {
  font-size: 15px;
  font-weight: 600;
  margin-bottom: 4px;
}

.step-body p {
  font-size: 14px;
  line-height: 1.6;
  color: var(--color-text-muted);
}

.density-explainer {
  background: var(--color-dark);
  color: var(--color-text-inverse);
  padding: 64px 40px;
}

.density-explainer .inner {
  max-width: 860px;
  margin: 0 auto;
}

.density-explainer h2 {
  color: var(--color-text-inverse);
  margin-bottom: 12px;
}

.density-explainer .section-label {
  color: var(--color-accent-on-dark);
}

.density-explainer .section-label::after {
  background: rgba(248, 250, 252, 0.18);
}

.density-explainer .section-intro {
  color: var(--color-text-inverse-muted);
}

.density-cards {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 20px;
  margin-top: 32px;
}

.density-card {
  border: 1px solid rgba(248, 250, 252, 0.18);
  padding: 24px;
  transition: border-color 0.2s;
}

.density-card:hover {
  border-color: rgba(248, 250, 252, 0.34);
}

.density-card .unit {
  font-family: var(--mono);
  font-size: 13px;
  color: var(--color-accent-on-dark);
  margin-bottom: 10px;
  font-weight: 600;
}

.density-card .conv {
  font-family: var(--mono);
  font-size: 20px;
  font-weight: 600;
}

.density-card p {
  font-size: 13px;
  color: var(--color-text-inverse-soft);
  margin-top: 8px;
  line-height: 1.5;
}

.faq-list {
  display: flex;
  flex-direction: column;
  gap: 0;
}

.faq-item {
  border-bottom: 1px solid var(--rule);
  border-left: 3px solid transparent;
  padding-left: 16px;
  margin-left: -19px;
  transition:
    border-left-color 0.2s,
    background 0.2s;
  border-radius: 0 2px 2px 0;
}

.faq-item.open {
  border-left-color: var(--accent);
  background: var(--color-accent-soft);
}

.faq-q {
  width: 100%;
  font-family: var(--serif);
  font-size: 20px;
  font-weight: 700;
  color: var(--ink);
  padding: 22px 0;
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
  user-select: none;
  gap: 12px;
  border: 0;
  background: transparent;
  text-align: left;
}

.faq-toggle {
  width: 32px;
  height: 32px;
  flex-shrink: 0;
  border: 2px solid var(--rule);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  transition:
    border-color 0.2s,
    background 0.2s;
  position: relative;
}

.faq-item.open .faq-toggle {
  border-color: var(--accent);
  background: var(--accent);
}

.faq-toggle::before,
.faq-toggle::after {
  content: "";
  position: absolute;
  background: var(--ink);
  border-radius: 1px;
  transition:
    transform 0.25s,
    background 0.2s,
    opacity 0.2s;
}

.faq-toggle::before {
  width: 12px;
  height: 2px;
}

.faq-toggle::after {
  width: 2px;
  height: 12px;
}

.faq-item.open .faq-toggle::before,
.faq-item.open .faq-toggle::after {
  background: #fff;
}

.faq-item.open .faq-toggle::after {
  transform: rotate(90deg);
  opacity: 0;
}

.faq-a {
  font-size: 16px;
  line-height: 1.75;
  color: #1f2937;
  padding-bottom: 24px;
  display: none;
  max-width: 680px;
}

.faq-item.open .faq-a {
  display: block;
}

.faq-a strong {
  color: var(--ink);
  font-weight: 600;
}

.tone-info {
  background: var(--info-50);
  color: var(--info-700);
}

.tone-warning {
  background: var(--warning-50);
  color: var(--warning-700);
}

/* HEADER */
.masthead-top {
  background: var(--ue-hdr-bg);
  border-bottom: 1px solid var(--ue-hdr-border);
  position: sticky;
  top: 0;
  z-index: 500;
  box-shadow: 0 1px 8px rgba(0, 0, 0, 0.06);
}

.masthead-top .masthead {
  max-width: 1360px;
  margin: 0 auto;
  padding: 0 24px;
  height: 62px;
  display: flex;
  align-items: center;
  gap: 4px;
}

.masthead-top .logo {
  display: flex;
  align-items: center;
  gap: 8px;
  font-family: var(--ue-serif);
  font-size: 18px;
  font-weight: 700;
  color: var(--ue-text);
  text-decoration: none;
  margin-right: 24px;
  flex-shrink: 0;
  letter-spacing: -0.01em;
}

.masthead-top .logo-icon {
  width: 30px;
  height: 30px;
  background: var(--ue-primary);
  border-radius: 7px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: #fff;
  flex-shrink: 0;
}

.masthead-top .logo-icon svg {
  width: 16px;
  height: 16px;
  stroke-width: 2.5;
}

.masthead-top .main-nav {
  display: flex;
  align-items: center;
  gap: 2px;
  flex: 1;
}

.masthead-top .nav-item {
  position: relative;
}

.masthead-top .nav-link {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 8px 12px;
  border-radius: 7px;
  font-family: var(--ue-sans);
  font-size: 13.5px;
  font-weight: 500;
  color: var(--ue-hdr-muted);
  text-decoration: none;
  background: transparent;
  border: none;
  cursor: pointer;
  transition:
    background 0.15s,
    color 0.15s;
  white-space: nowrap;
}

.masthead-top .nav-link svg {
  width: 14px;
  height: 14px;
  flex-shrink: 0;
}

.masthead-top .nav-link:hover,
.masthead-top .nav-link.active {
  background: var(--ue-hdr-hover-bg);
  color: var(--ue-text);
}

.masthead-top .nav-chevron svg {
  width: 13px;
  height: 13px;
  transition: transform 0.2s;
}

.masthead-top .nav-item:has(.mega-dropdown:not([hidden])) .nav-chevron svg {
  transform: rotate(180deg);
}

.masthead-top .mega-dropdown {
  position: absolute;
  top: calc(100% + 8px);
  left: 0;
  background: #fff;
  border: 1px solid var(--ue-hdr-border);
  border-radius: 12px;
  box-shadow:
    0 8px 32px rgba(0, 0, 0, 0.12),
    0 2px 8px rgba(0, 0, 0, 0.06);
  padding: 16px;
  min-width: 280px;
  z-index: 600;
  animation: ueDropIn 0.15s ease;
}

.masthead-top .mega-dropdown.wide {
  min-width: 580px;
}

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

.masthead-top .dropdown-header {
  display: flex;
  align-items: flex-start;
  gap: 12px;
  padding-bottom: 14px;
  margin-bottom: 14px;
  border-bottom: 1px solid var(--ue-hdr-border);
}

.masthead-top .dropdown-header-icon {
  width: 36px;
  height: 36px;
  border-radius: 8px;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.masthead-top .dropdown-header-icon svg {
  width: 18px;
  height: 18px;
}

.masthead-top .dropdown-header h4 {
  font-family: var(--ue-sans);
  font-size: 13px;
  font-weight: 700;
  color: var(--ue-text);
  margin: 0 0 2px;
}

.masthead-top .dropdown-header p {
  font-size: 12px;
  color: var(--ue-hdr-muted);
  line-height: 1.4;
  margin: 0;
}

.masthead-top .dropdown-cols {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 4px;
}

.masthead-top .dropdown-cols.cols-3 {
  grid-template-columns: 1fr 1fr 1fr;
}

.masthead-top .dropdown-cols.cols-2 {
  grid-template-columns: 1fr 1fr;
}

.masthead-top .dropdown-link {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 10px 12px;
  border-radius: 8px;
  text-decoration: none;
  color: var(--ue-text);
  font-size: 13px;
  font-weight: 500;
  transition: background 0.12s;
}

.masthead-top .dropdown-link:hover {
  background: var(--ue-hdr-hover-bg);
}

.masthead-top .dropdown-link-icon {
  width: 28px;
  height: 28px;
  background: var(--ue-hdr-hover-bg);
  border-radius: 6px;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  color: var(--ue-primary);
}

.masthead-top .dropdown-link-icon svg {
  width: 14px;
  height: 14px;
}

.masthead-top .dropdown-link-text {
  display: flex;
  flex-direction: column;
  gap: 1px;
}

.masthead-top .dropdown-link-desc {
  font-size: 11px;
  color: var(--ue-hdr-muted);
  font-weight: 400;
}

.masthead-top .nav-right {
  margin-left: auto;
  display: flex;
  align-items: center;
  gap: 8px;
}

.masthead-top .btn,
.site-footer .btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 8px 16px;
  border-radius: 8px;
  font-family: var(--ue-sans);
  font-size: 13px;
  font-weight: 600;
  text-decoration: none;
  border: none;
  cursor: pointer;
  transition:
    background 0.15s,
    color 0.15s,
    transform 0.15s;
}

.masthead-top .btn svg,
.site-footer .btn svg {
  width: 14px;
  height: 14px;
}

.masthead-top .btn-primary,
.site-footer .btn-primary {
  background: var(--ue-primary);
  color: #fff;
}

.masthead-top .btn-primary:hover,
.site-footer .btn-primary:hover {
  background: var(--ue-primary-hover);
}

.masthead-top .btn-sm {
  padding: 6px 14px;
  font-size: 12.5px;
}

.masthead-top .menu-toggle {
  display: none;
  width: 36px;
  height: 36px;
  border: 1px solid var(--ue-hdr-border);
  border-radius: 8px;
  background: transparent;
  cursor: pointer;
  align-items: center;
  justify-content: center;
  color: var(--ue-text);
}

.masthead-top .menu-toggle svg {
  width: 18px;
  height: 18px;
}

/* reelated link  */

/* ── Section wrapper ── */
.link-container {
  padding: 40px 0;
  border-top: 1px solid var(--color-border-soft);
}

/* ── Section header ── */
.section-header {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 24px;
}

.section-icon {
  width: 36px;
  height: 36px;
  border-radius: 8px;
  background: var(--color-ink);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.section-header h2 {
  font-family: var(--serif);
  font-size: 22px;
  font-weight: 700;
  line-height: 1.2;
  letter-spacing: -0.01em;
  white-space: nowrap;
}

.section-divider {
  flex: 1;
  height: 1px;
  background: var(--color-border);
}

/* ── Links grid ── */
.links-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 8px;
  margin-bottom: 20px;
}

.tool-link {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px 16px;
  background: var(--color-surface);
  border: 1px solid var(--color-border-soft);
  border-radius: 6px;
  font-size: 13.5px;
  font-weight: 500;
  color: var(--color-text-muted);
  text-decoration: none;
  box-shadow: var(--shadow-sm);
  transition:
    color 0.15s,
    border-color 0.15s,
    background 0.15s,
    transform 0.15s,
    box-shadow 0.15s;
}

.tool-link::after {
  content: "→";
  margin-left: auto;
  font-size: 12px;
  color: var(--color-border);
  transition:
    color 0.15s,
    transform 0.15s;
}

.tool-link:hover {
  color: var(--color-accent);
  border-color: var(--color-accent);
  background: var(--color-accent-soft);
  transform: translateY(-1px);
  box-shadow: var(--shadow-hover);
}

.tool-link:hover::after {
  color: var(--color-accent);
  transform: translateX(3px);
}

.tool-link:focus-visible {
  outline: none;
  box-shadow: var(--focus-ring);
}

/* ── View all ── */
.view-all-link {
  display: inline-flex;
  align-items: center;
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--color-accent);
  text-decoration: none;
  border-bottom: 1px solid transparent;
  transition:
    border-color 0.15s,
    color 0.15s;
}

.view-all-link:hover {
  color: var(--color-accent-hover);
  border-bottom-color: var(--color-accent-hover);
}

.view-all-link:focus-visible {
  outline: none;
  box-shadow: var(--focus-ring);
}
/* FOOTER */
.site-footer {
  background: var(--ue-ftr-bg);
  color: var(--ue-ftr-text);
  font-family: var(--ue-sans);
  margin-top: 48px;
}

.site-footer .footer-top {
  max-width: 1360px;
  margin: 0 auto;
  padding: 56px 24px 40px;
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr 1fr;
  gap: 40px;
  border-bottom: 1px solid var(--ue-ftr-border);
}

.site-footer .footer-logo {
  display: inline-flex;
  align-items: center;
  gap: 9px;
  font-family: var(--ue-serif);
  font-size: 19px;
  font-weight: 700;
  color: #fff;
  text-decoration: none;
  margin-bottom: 14px;
}

.site-footer .footer-logo-icon {
  width: 32px;
  height: 32px;
  background: var(--ue-primary);
  border-radius: 8px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: #fff;
  flex-shrink: 0;
}

.site-footer .footer-logo-icon svg {
  width: 16px;
  height: 16px;
  stroke-width: 2.5;
}

.site-footer .footer-tagline {
  font-size: 13px;
  color: var(--ue-ftr-muted);
  line-height: 1.7;
  max-width: 280px;
  margin-top: 4px;
}

.site-footer .footer-col-title {
  font-family: var(--ue-mono);
  font-size: 10px;
  font-weight: 600;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: #fff;
  margin-bottom: 14px;
}

.site-footer .footer-links {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.site-footer .footer-link {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 5px 0;
  font-size: 13px;
  color: var(--ue-ftr-muted);
  text-decoration: none;
  transition: color 0.15s;
}

.site-footer .footer-link svg {
  width: 13px;
  height: 13px;
  flex-shrink: 0;
  opacity: 0.8;
}

.site-footer .footer-link:hover {
  color: #fff;
}

.site-footer .footer-link:hover svg {
  opacity: 1;
}

.site-footer .footer-mid {
  max-width: 1360px;
  margin: 0 auto;
  padding: 28px 24px;
  display: flex;
  align-items: center;
  gap: 32px;
  border-bottom: 1px solid var(--ue-ftr-border);
  flex-wrap: wrap;
}

.site-footer .footer-mid p:first-child {
  font-size: 14px;
  font-weight: 600;
  color: #fff;
  margin: 0 0 2px;
}

.site-footer .footer-mid p:last-of-type {
  font-size: 12px;
  color: var(--ue-ftr-muted);
  margin: 0;
}

.site-footer .footer-newsletter {
  display: flex;
  gap: 8px;
  flex-shrink: 0;
}

.site-footer .footer-newsletter input {
  padding: 9px 14px;
  background: var(--ue-ftr-surface);
  border: 1px solid var(--ue-ftr-border);
  border-radius: 7px;
  font-family: var(--ue-sans);
  font-size: 13px;
  color: var(--ue-ftr-text);
  outline: none;
  width: 220px;
  transition:
    border-color 0.15s,
    box-shadow 0.15s;
}

.site-footer .footer-newsletter input::placeholder {
  color: var(--ue-ftr-muted);
  opacity: 1;
}

.site-footer .footer-newsletter input:focus {
  border-color: var(--ue-ftr-accent);
  box-shadow: 0 0 0 3px rgba(129, 140, 248, 0.22);
}

.site-footer .footer-mid-right {
  margin-left: auto;
  display: flex;
  gap: 20px;
  flex-shrink: 0;
}

.site-footer .footer-mid-link {
  font-size: 12px;
  color: var(--ue-ftr-muted);
  text-decoration: none;
  transition: color 0.15s;
}

.site-footer .footer-mid-link:hover {
  color: #fff;
}

.site-footer .footer-bottom {
  max-width: 1360px;
  margin: 0 auto;
  padding: 18px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 12px;
}

.site-footer .footer-bottom p {
  font-size: 12px;
  color: var(--ue-ftr-muted);
  margin: 0;
}

.site-footer .footer-bottom-right {
  display: flex;
  align-items: center;
  gap: 20px;
  font-size: 12px;
  color: var(--ue-ftr-muted);
  flex-wrap: wrap;
}

.site-footer .footer-bottom-right svg {
  width: 12px;
  height: 12px;
  color: var(--ue-primary);
  vertical-align: middle;
}

.site-footer .kbd {
  display: inline-flex;
  align-items: center;
  padding: 1px 6px;
  background: var(--ue-ftr-surface);
  border: 1px solid var(--ue-ftr-border);
  border-radius: 4px;
  font-family: var(--ue-mono);
  font-size: 10px;
  color: var(--ue-ftr-text);
}

@media (max-width: 1100px) {
  .site-footer .footer-top {
    grid-template-columns: 1fr 1fr 1fr;
  }

  .site-footer .footer-brand {
    grid-column: 1 / -1;
  }
}

@media (max-width: 900px) {
  .masthead-top .masthead {
    padding: 0 16px;
  }

  .masthead-top .main-nav {
    display: none;
    position: absolute;
    top: 62px;
    left: 0;
    right: 0;
    background: #fff;
    border-bottom: 1px solid var(--ue-hdr-border);
    padding: 12px 16px;
    box-shadow: 0 12px 24px rgba(0, 0, 0, 0.08);
    flex-direction: column;
    align-items: stretch;
    gap: 8px;
  }

  .masthead-top .main-nav.open {
    display: flex;
  }

  .masthead-top .nav-item {
    width: 100%;
  }

  .masthead-top .nav-link {
    width: 100%;
    justify-content: space-between;
  }

  .masthead-top .mega-dropdown,
  .masthead-top .mega-dropdown.wide {
    position: static;
    min-width: 100%;
    margin-top: 8px;
  }
  .masthead-top .nav-right .btn {
    display: none;
  }
  .masthead-top .menu-toggle {
    display: inline-flex;
  }

  .site-footer .footer-top {
    grid-template-columns: 1fr 1fr;
  }

  .site-footer .footer-mid {
    flex-direction: column;
    align-items: flex-start;
  }

  .site-footer .footer-mid-right {
    margin-left: 0;
  }
}

@media (max-width: 640px) {
  .explain-grid {
    grid-template-columns: 1fr;
  }

  .density-cards {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 600px) {
  .hero {
    padding: 20px 20px 24px;
  }

  .hero-inner {
    grid-template-columns: 1fr;
    gap: 12px;
  }

  .hero-facts {
    flex-direction: row;
    flex-wrap: wrap;
    gap: 8px 16px;
  }

  .converter-wrap {
    padding: 0 16px;
  }

  .tab-panel {
    padding: 24px 20px 20px;
  }

  .conv-row {
    grid-template-columns: 1fr;
    gap: 12px;
  }

  .field-group input {
    font-size: 32px;
    padding: 14px 16px;
  }

  .section {
    padding: 48px 20px;
  }

  .density-explainer {
    padding: 48px 20px;
  }

  .site-footer .footer-top {
    grid-template-columns: 1fr;
    gap: 28px;
    padding: 40px 16px 28px;
  }

  .site-footer .footer-mid {
    padding: 22px 16px;
  }

  .site-footer .footer-newsletter {
    width: 100%;
    flex-direction: column;
  }

  .site-footer .footer-newsletter input {
    width: 100%;
  }

  .site-footer .footer-bottom {
    padding: 16px;
  }
}

@keyframes fadeUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.converter-card {
  animation: fadeUp 0.4s 0.1s ease both;
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }

  .swap-btn:hover {
    transform: none;
  }
}