/* ==========================================================
   www.zhaku.net - design system
   Light/dark via CSS custom properties, mobile-first layout.
   ========================================================== */

:root {
  --bg: #f6f7fb;
  --bg-card: #ffffff;
  --bg-inset: #eef0f6;
  --text: #16203a;
  --text-soft: #56607a;
  --text-faint: #8b93ab;
  --border: #e3e6ef;
  --accent: #4f46e5;
  --accent-2: #0ea5e9;
  --accent-soft: #eef2ff;
  --good: #059669;
  --good-soft: #ecfdf5;
  --warn: #d97706;
  --warn-soft: #fffbeb;
  --danger: #dc2626;
  --shadow: 0 1px 2px rgba(22, 32, 58, .05), 0 8px 24px -12px rgba(22, 32, 58, .18);
  --shadow-lg: 0 2px 4px rgba(22, 32, 58, .06), 0 20px 44px -16px rgba(22, 32, 58, .25);
  --radius: 14px;
  --radius-sm: 9px;
  --font: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --mono: ui-monospace, "SF Mono", "Cascadia Mono", Consolas, monospace;
}

[data-theme="dark"] {
  --bg: #0d1220;
  --bg-card: #161d31;
  --bg-inset: #1e2740;
  --text: #e7eaf3;
  --text-soft: #a4adc6;
  --text-faint: #6c7692;
  --border: #273151;
  --accent: #818cf8;
  --accent-2: #38bdf8;
  --accent-soft: #232b4d;
  --good: #34d399;
  --good-soft: #10281f;
  --warn: #fbbf24;
  --warn-soft: #2b2110;
  --danger: #f87171;
  --shadow: 0 1px 2px rgba(0, 0, 0, .4), 0 8px 24px -12px rgba(0, 0, 0, .55);
  --shadow-lg: 0 2px 4px rgba(0, 0, 0, .45), 0 20px 44px -16px rgba(0, 0, 0, .6);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  font-size: 16px;
  transition: background .25s, color .25s;
}

img, svg { vertical-align: middle; }
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

.container { max-width: 1080px; margin: 0 auto; padding: 0 20px; }

.skip-link {
  position: absolute; left: -999px; top: 8px; z-index: 100;
  background: var(--accent); color: #fff; padding: 8px 16px; border-radius: 8px;
}
.skip-link:focus { left: 8px; }

/* ---------- PWA install banner ---------- */
.install-banner {
  background: linear-gradient(100deg, #312e81, #1e3a8a);
  color: #fff;
}
.install-banner-inner {
  display: flex; align-items: center; justify-content: space-between;
  gap: 12px; padding-top: 10px; padding-bottom: 10px;
}
.install-banner-info { display: flex; align-items: center; gap: 11px; min-width: 0; }
.install-banner-icon { border-radius: 8px; flex-shrink: 0; }
.install-banner-text { font-weight: 700; font-size: .98rem; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.install-banner-actions { display: flex; align-items: center; gap: 8px; flex-shrink: 0; }
.install-later {
  background: none; border: 0; color: rgba(255, 255, 255, .75);
  font: inherit; font-size: .9rem; font-weight: 550; cursor: pointer; padding: 8px 10px;
}
.install-later:hover { color: #fff; }
.install-btn {
  background: #fff; color: #312e81; border: 0; border-radius: 9px;
  padding: 9px 18px; font: inherit; font-size: .88rem; font-weight: 800;
  letter-spacing: .05em; cursor: pointer; box-shadow: 0 2px 8px rgba(0, 0, 0, .25);
  transition: transform .12s;
}
.install-btn:hover { transform: translateY(-1px); }
.install-ios-help {
  padding-bottom: 12px; font-size: .88rem; color: rgba(255, 255, 255, .9);
}
@media (max-width: 480px) {
  .install-banner-text { font-size: .92rem; }
  .install-btn { padding: 8px 14px; width: auto; }
}

/* ---------- header ---------- */
.site-header {
  position: sticky; top: 0; z-index: 50;
  background: color-mix(in srgb, var(--bg-card) 82%, transparent);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}
.header-inner { display: flex; align-items: center; gap: 20px; height: 62px; }
.brand { display: flex; align-items: center; gap: 10px; color: var(--text); font-weight: 700; }
.brand:hover { text-decoration: none; }
.brand-name { font-size: 1.18rem; letter-spacing: -.02em; }
.brand-dot { color: var(--accent); }

.main-nav { display: flex; align-items: center; gap: 4px; margin-left: auto; }
.main-nav > a, .nav-drop-btn {
  display: inline-flex; align-items: center; gap: 6px;
  padding: 8px 13px; border-radius: 9px; border: 0; background: none;
  color: var(--text-soft); font: inherit; font-weight: 550; cursor: pointer;
}
.main-nav > a:hover, .nav-drop-btn:hover { background: var(--bg-inset); color: var(--text); text-decoration: none; }
.nav-group { position: relative; }
.nav-drop {
  position: absolute; top: calc(100% + 8px); left: 0; min-width: 230px;
  background: var(--bg-card); border: 1px solid var(--border); border-radius: 12px;
  box-shadow: var(--shadow-lg); padding: 8px; display: none; flex-direction: column;
}
.nav-group.open .nav-drop { display: flex; }
.nav-drop a { padding: 9px 12px; border-radius: 8px; color: var(--text); font-weight: 500; }
.nav-drop a:hover { background: var(--accent-soft); text-decoration: none; }

.header-actions { display: flex; align-items: center; gap: 8px; }
.theme-toggle {
  display: inline-flex; align-items: center; justify-content: center;
  width: 38px; height: 38px; border-radius: 10px; border: 1px solid var(--border);
  background: var(--bg-card); color: var(--text-soft); cursor: pointer;
}
.theme-toggle:hover { color: var(--text); }
.icon-moon { display: none; }
[data-theme="dark"] .icon-moon { display: block; }
[data-theme="dark"] .icon-sun { display: none; }

.burger { display: none; flex-direction: column; justify-content: center; gap: 5px; width: 40px; height: 38px; border: 1px solid var(--border); border-radius: 10px; background: var(--bg-card); cursor: pointer; padding: 0 9px; }
.burger span { display: block; height: 2px; background: var(--text); border-radius: 2px; transition: transform .2s, opacity .2s; }
.burger[aria-expanded="true"] span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.burger[aria-expanded="true"] span:nth-child(2) { opacity: 0; }
.burger[aria-expanded="true"] span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* ---------- hero ---------- */
.hero { padding: 56px 0 30px; text-align: center; }
.hero h1 {
  font-size: clamp(1.9rem, 4.5vw, 3rem); line-height: 1.15; letter-spacing: -.03em;
  margin: 0 0 14px; font-weight: 800;
}
.hero .accent-text {
  background: linear-gradient(100deg, var(--accent), var(--accent-2));
  -webkit-background-clip: text; background-clip: text; color: transparent;
}
.hero p { max-width: 640px; margin: 0 auto; color: var(--text-soft); font-size: 1.08rem; }

.page-hero { padding: 40px 0 8px; }
.page-hero h1 { font-size: clamp(1.7rem, 4vw, 2.4rem); letter-spacing: -.02em; margin: 8px 0 10px; }
.page-hero .lede { color: var(--text-soft); font-size: 1.06rem; max-width: 720px; margin: 0; }
.breadcrumbs { font-size: .85rem; color: var(--text-faint); }
.breadcrumbs a { color: var(--text-faint); }
.breadcrumbs a:hover { color: var(--accent); }

/* ---------- calculator card ---------- */
.calc-wrap { padding: 26px 0 10px; }
.calc-card {
  background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius);
  box-shadow: var(--shadow-lg); padding: 26px; max-width: 780px; margin: 0 auto;
}
.calc-card h2 { margin-top: 0; }

.field { margin-bottom: 16px; }
.field label { display: block; font-weight: 600; font-size: .92rem; margin-bottom: 6px; }
.field .hint { font-weight: 400; color: var(--text-faint); font-size: .82rem; margin-left: 6px; }

.input-affix { display: flex; align-items: stretch; }
.input-affix .affix {
  display: flex; align-items: center; padding: 0 13px; background: var(--bg-inset);
  border: 1px solid var(--border); color: var(--text-soft); font-weight: 600;
}
.input-affix .affix.pre { border-right: 0; border-radius: var(--radius-sm) 0 0 var(--radius-sm); }
.input-affix .affix.post { border-left: 0; border-radius: 0 var(--radius-sm) var(--radius-sm) 0; }
.input-affix input { border-radius: 0 var(--radius-sm) var(--radius-sm) 0; flex: 1; min-width: 0; }
.input-affix input.has-post { border-radius: 0; }
.input-affix .affix.pre + input:last-child { border-radius: 0 var(--radius-sm) var(--radius-sm) 0; }

input[type="number"], input[type="text"], input[type="email"], select, textarea {
  width: 100%; padding: 11px 13px; font: inherit; color: var(--text);
  background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius-sm);
  transition: border-color .15s, box-shadow .15s;
}
input:focus, select:focus, textarea:focus {
  outline: none; border-color: var(--accent);
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--accent) 22%, transparent);
}
input[type="number"] { -moz-appearance: textfield; }
input::-webkit-outer-spin-button, input::-webkit-inner-spin-button { -webkit-appearance: none; margin: 0; }

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

/* segmented control */
.segmented { display: inline-flex; background: var(--bg-inset); border: 1px solid var(--border); border-radius: 11px; padding: 4px; gap: 4px; flex-wrap: wrap; }
.segmented button {
  border: 0; background: none; padding: 8px 15px; border-radius: 8px; font: inherit;
  font-weight: 600; color: var(--text-soft); cursor: pointer; transition: background .15s, color .15s;
}
.segmented button.active { background: var(--bg-card); color: var(--accent); box-shadow: var(--shadow); }

/* buttons */
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  padding: 12px 22px; border-radius: 11px; border: 0; font: inherit; font-weight: 650;
  cursor: pointer; transition: transform .12s, box-shadow .15s, background .15s;
}
.btn-primary { background: linear-gradient(100deg, var(--accent), var(--accent-2)); color: #fff; box-shadow: 0 6px 18px -6px color-mix(in srgb, var(--accent) 60%, transparent); }
.btn-primary:hover { transform: translateY(-1px); }
.btn-secondary { background: var(--bg-inset); color: var(--text); border: 1px solid var(--border); }
.btn-secondary:hover { border-color: var(--text-faint); }
.btn-row { display: flex; gap: 10px; flex-wrap: wrap; margin-top: 6px; }

/* results */
.result-panel {
  margin-top: 22px; border-radius: var(--radius); overflow: hidden;
  border: 1px solid color-mix(in srgb, var(--accent) 35%, var(--border));
  background: var(--accent-soft);
  animation: pop .25s ease;
  display: none;
}
.result-panel.show { display: block; }
@keyframes pop { from { opacity: 0; transform: translateY(6px); } to { opacity: 1; transform: none; } }
.result-hero { padding: 20px 22px 6px; }
.result-hero .label { font-size: .85rem; font-weight: 650; text-transform: uppercase; letter-spacing: .06em; color: var(--text-soft); }
.result-hero .value { font-size: clamp(1.7rem, 5vw, 2.4rem); font-weight: 800; letter-spacing: -.02em; line-height: 1.2; }
.result-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(150px, 1fr)); gap: 1px; background: var(--border); margin-top: 14px; }
.result-cell { background: var(--bg-card); padding: 13px 18px; }
.result-cell .k { font-size: .8rem; color: var(--text-faint); font-weight: 600; }
.result-cell .v { font-size: 1.12rem; font-weight: 700; font-variant-numeric: tabular-nums; }
.result-cell .v.good { color: var(--good); }
.result-note { padding: 10px 22px 14px; font-size: .85rem; color: var(--text-soft); }
.workings { font-family: var(--mono); font-size: .84rem; background: var(--bg-inset); border-radius: 8px; padding: 10px 14px; margin: 10px 22px 16px; color: var(--text-soft); overflow-x: auto; white-space: nowrap; }

/* copy-to-clipboard cells */
.copyable { cursor: pointer; position: relative; }
.copyable:hover { background: var(--accent-soft); }
.copyable.copied::after {
  content: "Copied!"; position: absolute; top: 6px; right: 10px; font-size: .7rem;
  background: var(--good); color: #fff; padding: 2px 8px; border-radius: 20px;
}

/* ---------- cards grid (home) ---------- */
.section-label { text-align:left; font-size: .85rem; font-weight: 700; text-transform: uppercase; letter-spacing: .1em; color: var(--text-faint); margin: 34px 0 14px; }
.card-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(250px, 1fr)); gap: 16px; }
.tool-card {
  display: flex; flex-direction: column; gap: 10px; padding: 22px;
  background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius);
  color: var(--text); box-shadow: var(--shadow); transition: transform .15s, box-shadow .15s, border-color .15s;
}
.tool-card:hover { transform: translateY(-3px); box-shadow: var(--shadow-lg); border-color: color-mix(in srgb, var(--accent) 45%, var(--border)); text-decoration: none; }
.tool-card h3 { margin: 0; font-size: 1.06rem; }
.tool-card p { margin: 0; color: var(--text-soft); font-size: .92rem; }
.tool-card .go { margin-top: auto; color: var(--accent); font-weight: 650; font-size: .9rem; }
.tool-icon {
  width: 42px; height: 42px; border-radius: 11px; display: flex; align-items: center; justify-content: center;
  background: var(--accent-soft); color: var(--accent);
}

/* ---------- content sections ---------- */
.content-section { max-width: 780px; margin: 34px auto; padding: 0 20px; }
.content-section h2 { font-size: 1.45rem; letter-spacing: -.01em; margin: 0 0 12px; }
.content-section h3 { font-size: 1.1rem; margin: 22px 0 8px; }
.content-section p, .content-section li { color: var(--text-soft); }
.content-section strong { color: var(--text); }

.example-box {
  background: var(--bg-card); border: 1px solid var(--border); border-left: 4px solid var(--accent);
  border-radius: var(--radius-sm); padding: 16px 20px; margin: 16px 0;
}
.example-box .ex-title { font-weight: 700; color: var(--text); margin-bottom: 4px; }
.example-box p { margin: 6px 0; }

.callout { border-radius: var(--radius-sm); padding: 14px 18px; margin: 16px 0; font-size: .95rem; }
.callout.warn { background: var(--warn-soft); border: 1px solid color-mix(in srgb, var(--warn) 40%, transparent); color: var(--text); }
.callout.good { background: var(--good-soft); border: 1px solid color-mix(in srgb, var(--good) 40%, transparent); color: var(--text); }

/* tables */
.table-wrap { overflow-x: auto; margin: 16px 0; border: 1px solid var(--border); border-radius: var(--radius-sm); }
table.data { border-collapse: collapse; width: 100%; font-size: .93rem; background: var(--bg-card); }
table.data th, table.data td { text-align: left; padding: 10px 14px; border-bottom: 1px solid var(--border); }
table.data th { background: var(--bg-inset); font-size: .82rem; text-transform: uppercase; letter-spacing: .05em; color: var(--text-soft); }
table.data tr:last-child td { border-bottom: 0; }
table.data td.num { font-variant-numeric: tabular-nums; text-align: right; }

/* FAQs */
.faq-list { display: flex; flex-direction: column; gap: 10px; }
.faq-item { background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius-sm); }
.faq-item summary { padding: 14px 18px; font-weight: 650; cursor: pointer; list-style: none; display: flex; justify-content: space-between; align-items: center; gap: 12px; }
.faq-item summary::-webkit-details-marker { display: none; }
.faq-item summary::after { content: "+"; font-size: 1.3rem; color: var(--accent); flex-shrink: 0; transition: transform .2s; }
.faq-item[open] summary::after { transform: rotate(45deg); }
.faq-answer { padding: 0 18px 14px; color: var(--text-soft); }
.faq-answer p { margin: 0; }

/* related links */
.related-strip { max-width: 780px; margin: 30px auto 10px; padding: 0 20px; }
.related-strip h2 { font-size: 1.1rem; }
.chip-row { display: flex; flex-wrap: wrap; gap: 10px; }
.chip {
  padding: 8px 16px; border-radius: 30px; background: var(--bg-card);
  border: 1px solid var(--border); color: var(--text); font-size: .9rem; font-weight: 550;
}
.chip:hover { border-color: var(--accent); color: var(--accent); text-decoration: none; }

/* ---------- forms / contact ---------- */
.form-card { max-width: 640px; margin: 20px auto 40px; background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius); box-shadow: var(--shadow); padding: 26px; }
.notice { padding: 13px 17px; border-radius: var(--radius-sm); margin-bottom: 16px; font-size: .95rem; }
.notice.ok { background: var(--good-soft); color: var(--good); border: 1px solid color-mix(in srgb, var(--good) 40%, transparent); }
.notice.err { background: var(--warn-soft); color: var(--warn); border: 1px solid color-mix(in srgb, var(--warn) 40%, transparent); }
.hp-field { position: absolute; left: -9999px; }

/* ---------- footer ---------- */
.site-footer { margin-top: 60px; border-top: 1px solid var(--border); background: var(--bg-card); }
.footer-grid { display: grid; grid-template-columns: 2fr 1fr 1fr 1fr 1fr; gap: 26px; padding: 40px 20px 20px; }
.footer-grid h3 { font-size: .82rem; text-transform: uppercase; letter-spacing: .08em; color: var(--text-faint); margin: 0 0 10px; }
.footer-grid nav { display: flex; flex-direction: column; gap: 7px; }
.footer-grid nav a { color: var(--text-soft); font-size: .92rem; }
.footer-grid nav a:hover { color: var(--accent); }
.footer-brand p { color: var(--text-faint); font-size: .9rem; max-width: 260px; }
.footer-note { border-top: 1px solid var(--border); padding-top: 16px; padding-bottom: 22px; }
.footer-note p { color: var(--text-faint); font-size: .82rem; margin: 0; }

/* ---------- responsive ---------- */
@media (max-width: 860px) {
  .burger { display: flex; }
  .header-actions { margin-left: auto; }
  .main-nav {
    display: none; position: absolute; top: 62px; left: 0; right: 0;
    background: var(--bg-card); border-bottom: 1px solid var(--border);
    flex-direction: column; align-items: stretch; padding: 12px 16px 18px; gap: 2px;
    box-shadow: var(--shadow-lg);
  }
  .main-nav.open { display: flex; }
  .main-nav > a { padding: 12px 10px; }
  .nav-drop-btn { width: 100%; justify-content: space-between; padding: 12px 10px; }
  .nav-drop { position: static; border: 0; box-shadow: none; padding: 0 0 4px 12px; background: none; }
  .field-row, .field-row-3 { grid-template-columns: 1fr; }
  .footer-grid { grid-template-columns: 1fr 1fr; }
  .calc-card { padding: 20px 16px; }
  .hero { padding: 40px 0 20px; }
}
@media (max-width: 480px) {
  .footer-grid { grid-template-columns: 1fr; }
  .segmented { width: 100%; }
  .segmented button { flex: 1; padding: 8px 6px; font-size: .88rem; }
  .btn { width: 100%; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation: none !important; transition: none !important; }
  html { scroll-behavior: auto; }
}