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

:root {
  --bg: #ffffff;
  --surface: #f8fafc;
  --border: #e2e8f0;
  --accent: #2563eb;
  --accent-hover: #1d4ed8;
  --accent-tint: #eff6ff;
  --text: #0f172a;
  --muted: #64748b;
  --success: #16a34a;
  --warning: #d97706;
  --danger: #dc2626;
  --radius: 12px;
}

html { scroll-behavior: smooth; }
body { background: var(--bg); color: var(--text); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif; font-size: 16px; line-height: 1.6; }
a { color: inherit; text-decoration: none; }
code { font-family: 'SF Mono', 'Fira Code', 'Consolas', monospace; font-size: 0.88em; }

/* ── NAV ─────────────────────────────────────────────────────── */
.navbar { position: sticky; top: 0; z-index: 100; display: flex; align-items: center; justify-content: space-between; padding: 0 40px; height: 56px; background: rgba(255,255,255,0.9); backdrop-filter: blur(10px); border-bottom: 1px solid var(--border); }
.nav-title { font-size: 0.98rem; font-weight: 700; color: var(--text); }
.navbar-actions { display: flex; align-items: center; gap: 16px; }
.lang-switch { font-size: 0.84rem; font-weight: 600; color: var(--muted); border-bottom: 1px solid transparent; transition: color 0.15s, border-color 0.15s; }
.lang-switch:hover { color: var(--accent); border-color: var(--accent); }

/* ── INTRO ───────────────────────────────────────────────────── */
.intro { padding: 56px 20px 40px; }
.intro-inner { max-width: 720px; margin: 0 auto; }
h1 { font-size: clamp(1.7rem, 4vw, 2.3rem); font-weight: 800; letter-spacing: -0.02em; margin-bottom: 14px; }
.intro-sub { font-size: 1.02rem; color: var(--muted); max-width: 600px; }

/* ── SECTIONS ────────────────────────────────────────────────── */
.section-inner { max-width: 900px; margin: 0 auto; padding: 0 20px; }
.section-inner--narrow { max-width: 680px; }
.section-title { font-size: 1.15rem; font-weight: 700; margin-bottom: 20px; letter-spacing: -0.01em; }

/* ── TOOL SECTION ────────────────────────────────────────────── */
.tool-section { padding: 0 20px 60px; }

.card { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 22px; margin-bottom: 16px; }
.card-label { font-size: 0.72rem; font-weight: 700; color: var(--muted); text-transform: uppercase; letter-spacing: 0.06em; margin-bottom: 14px; display: block; }

.tool-controls { display: flex; align-items: flex-end; gap: 18px; flex-wrap: wrap; }

.control-group { display: flex; flex-direction: column; gap: 7px; }
.control-label { font-size: 0.78rem; font-weight: 600; color: var(--muted); text-transform: uppercase; letter-spacing: 0.05em; }
.control-hint { font-weight: 500; text-transform: none; letter-spacing: normal; opacity: 0.75; }

/* version toggle */
.version-toggle { display: flex; gap: 0; background: #fff; border: 1px solid var(--border); border-radius: 8px; overflow: hidden; }
.version-btn { background: transparent; border: none; color: var(--muted); font-size: 0.86rem; font-weight: 600; padding: 8px 16px; cursor: pointer; transition: background 0.15s, color 0.15s; display: flex; flex-direction: column; align-items: center; gap: 1px; }
.version-btn.active { background: var(--accent); color: #fff; }
.version-btn:hover:not(.active) { background: var(--accent-tint); color: var(--text); }
.ver-hint { font-size: 0.66rem; font-weight: 400; opacity: 0.8; }

select { background: #fff; border: 1px solid var(--border); border-radius: 7px; color: var(--text); padding: 8px 11px; font-size: 0.88rem; outline: none; transition: border-color 0.15s; min-width: 150px; }
select:focus { border-color: var(--accent); }

/* quantity stepper */
.stepper { display: flex; align-items: stretch; border: 1px solid var(--border); border-radius: 7px; overflow: hidden; background: #fff; width: fit-content; }
.stepper-btn { background: var(--surface); border: none; color: var(--text); font-size: 1rem; font-weight: 700; width: 32px; cursor: pointer; transition: background 0.15s; }
.stepper-btn:hover { background: var(--accent-tint); color: var(--accent); }
.stepper-btn:active { background: var(--border); }
.stepper input[type="number"] { width: 64px; border: none; border-left: 1px solid var(--border); border-right: 1px solid var(--border); text-align: center; font-size: 0.88rem; color: var(--text); padding: 8px 4px; outline: none; -moz-appearance: textfield; }
.stepper input[type="number"]::-webkit-outer-spin-button,
.stepper input[type="number"]::-webkit-inner-spin-button { -webkit-appearance: none; margin: 0; }

/* output */
.output-header { display: flex; align-items: center; justify-content: space-between; margin-bottom: 10px; }
.result-count { font-size: 0.85rem; color: var(--muted); font-weight: 500; }
.output-actions { display: flex; gap: 8px; }

.uuid-list { display: flex; flex-direction: column; gap: 6px; margin-bottom: 16px; }

.uuid-row { display: flex; align-items: center; gap: 12px; background: #fff; border: 1px solid var(--border); border-radius: 8px; padding: 10px 14px; transition: border-color 0.15s; }
.uuid-row:hover { border-color: #c7d7fb; }

.uuid-text { flex: 1; font-family: 'SF Mono', 'Fira Code', 'Consolas', monospace; font-size: 0.87rem; color: var(--accent-hover); letter-spacing: 0.01em; word-break: break-all; }

.copy-btn { background: transparent; border: 1px solid var(--border); border-radius: 6px; color: var(--muted); padding: 5px 8px; cursor: pointer; transition: border-color 0.15s, color 0.15s; display: flex; align-items: center; flex-shrink: 0; }
.copy-btn:hover { border-color: var(--accent); color: var(--accent); }

/* validator */
.validator-card { margin-top: 0; }
.validator-row { display: flex; gap: 10px; }
.validator-row input { flex: 1; background: #fff; border: 1px solid var(--border); border-radius: 8px; color: var(--text); padding: 10px 14px; font-family: 'SF Mono', 'Fira Code', 'Consolas', monospace; font-size: 0.87rem; outline: none; transition: border-color 0.15s; }
.validator-row input:focus { border-color: var(--accent); }
.validator-row input::placeholder { font-family: -apple-system, sans-serif; color: var(--muted); font-size: 0.84rem; }

.validate-result { margin-top: 12px; padding: 13px 16px; border-radius: 9px; display: flex; align-items: flex-start; gap: 12px; font-size: 0.89rem; }
.validate-result.valid { background: #f0fdf4; border: 1px solid #bbf7d0; }
.validate-result.invalid { background: #fef2f2; border: 1px solid #fecaca; }
.vr-icon { font-size: 1.05rem; font-weight: 800; }
.validate-result.valid .vr-icon { color: var(--success); }
.validate-result.invalid .vr-icon { color: var(--danger); }
.vr-sub { font-family: 'SF Mono', 'Fira Code', monospace; font-size: 0.79rem; color: var(--muted); margin-top: 4px; }

/* ── BUTTONS ─────────────────────────────────────────────────── */
.btn { display: inline-flex; align-items: center; gap: 8px; padding: 10px 20px; border-radius: 8px; font-size: 0.88rem; font-weight: 600; cursor: pointer; border: none; transition: background 0.15s, transform 0.1s; white-space: nowrap; }
.btn:active { transform: scale(0.97); }
.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { background: var(--accent-hover); }
.btn-ghost { background: transparent; color: var(--muted); border: 1px solid var(--border); }
.btn-ghost:hover { color: var(--text); border-color: var(--muted); }
.btn-sm { padding: 6px 13px; font-size: 0.79rem; }

.hidden { display: none !important; }

/* ── REFERENCE (explanation + formats) ──────────────────────── */
.reference-section { padding: 0 20px 60px; border-top: 1px solid var(--border); padding-top: 50px; }
.ref-text { color: var(--muted); font-size: 0.94rem; margin-bottom: 14px; }
.ref-text strong { color: var(--text); }
.ref-text a, .policy-list a { color: var(--accent); text-decoration: underline; text-underline-offset: 2px; }
.ref-text a:hover, .policy-list a:hover { color: var(--accent-hover); }

.policy-content .section-title { margin-top: 32px; margin-bottom: 12px; }
.policy-content .section-title:first-child { margin-top: 0; }
.policy-list { color: var(--muted); font-size: 0.94rem; margin: 0 0 14px 1.1em; }
.policy-list li { margin-bottom: 6px; line-height: 1.6; }
.policy-list strong { color: var(--text); }

.format-table { border: 1px solid var(--border); border-radius: var(--radius); overflow: hidden; margin-top: 20px; }
.ft-row { display: grid; grid-template-columns: 130px 1fr; gap: 0; padding: 12px 18px; border-bottom: 1px solid var(--border); font-size: 0.86rem; align-items: center; }
.ft-row:last-child { border-bottom: none; }
.ft-header { background: var(--surface); font-size: 0.7rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.06em; color: var(--muted); }
.ft-row code { color: var(--accent-hover); font-size: 0.81rem; }

/* ── FAQ ─────────────────────────────────────────────────────── */
.faq-section { padding: 0 20px 60px; border-top: 1px solid var(--border); padding-top: 50px; }
.faq-list { display: flex; flex-direction: column; gap: 10px; }
.faq-item { background: var(--surface); border: 1px solid var(--border); border-radius: 9px; overflow: hidden; }
.faq-item summary { padding: 16px 18px; font-weight: 600; font-size: 0.92rem; cursor: pointer; list-style: none; display: flex; justify-content: space-between; align-items: center; user-select: none; }
.faq-item summary::after { content: '+'; font-size: 1.1rem; color: var(--accent); transition: transform 0.2s; }
.faq-item[open] summary::after { transform: rotate(45deg); }
.faq-item p { padding: 0 18px 16px; font-size: 0.88rem; color: var(--muted); line-height: 1.65; }
.faq-item code { color: var(--accent-hover); background: var(--accent-tint); padding: 1px 6px; border-radius: 4px; }

/* ── FOOTER ──────────────────────────────────────────────────── */
.site-footer { border-top: 1px solid var(--border); }
.footer-bottom { text-align: center; padding: 24px 20px; font-size: 0.82rem; color: var(--muted); }

/* ── RESPONSIVE ──────────────────────────────────────────────── */
@media (max-width: 640px) {
  .navbar { padding: 0 20px; }
  .intro { padding: 40px 16px 32px; }
  .tool-controls { flex-direction: column; align-items: stretch; }
  .validator-row { flex-direction: column; }
  .ft-row { grid-template-columns: 100px 1fr; font-size: 0.78rem; }
  .ft-row code { font-size: 0.7rem; word-break: break-all; }
}