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

:root {
  --bg: #0f1117;
  --surface: #1a1d27;
  --border: #2d3148;
  --accent: #6366f1;
  --accent-hover: #5254cc;
  --text: #e2e8f0;
  --text-muted: #94a3b8;
  --text-dim: #475569;
  --result-color: #a5f3fc;
  --error-color: #f87171;
}

body {
  font-family: system-ui, -apple-system, sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
}

/* ── Nav ── */
.nav {
  display: flex;
  align-items: center;
  gap: 16px;
  padding: 14px 24px;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
}

.nav-back {
  display: flex;
  align-items: center;
  gap: 6px;
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.875rem;
  transition: color 0.15s;
}

.nav-back:hover { color: var(--text); }

.nav-back svg { flex-shrink: 0; }

.nav-title {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text);
}

.nav-sep {
  color: var(--border);
  font-size: 1rem;
}

/* ── Tool page layout ── */
.tool-body {
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 40px 24px;
  min-height: calc(100vh - 53px);
}

/* ── Card ── */
.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 32px;
  width: 100%;
  max-width: 520px;
}

.card h1 {
  font-size: 1.4rem;
  font-weight: 600;
  margin-bottom: 28px;
  color: #f1f5f9;
  letter-spacing: 0.01em;
}

/* ── Form elements ── */
.form-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin-bottom: 16px;
}

.field {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.field.full { grid-column: 1 / -1; }

label {
  font-size: 0.8rem;
  color: var(--text-muted);
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

input[type="number"], select {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  font-size: 0.95rem;
  padding: 10px 12px;
  outline: none;
  transition: border-color 0.15s;
  width: 100%;
  -moz-appearance: textfield;
}

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

input[type="number"]:focus, select:focus { border-color: var(--accent); }

select option { background: var(--surface); }

.checkbox-row {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 20px;
}

.checkbox-row input[type="checkbox"] {
  width: 16px;
  height: 16px;
  accent-color: var(--accent);
  cursor: pointer;
}

.checkbox-row label {
  font-size: 0.875rem;
  text-transform: none;
  letter-spacing: normal;
  cursor: pointer;
  color: #cbd5e1;
}

/* ── Buttons ── */
.btn {
  width: 100%;
  padding: 12px;
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: 8px;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s, transform 0.1s;
}

.btn:hover { background: var(--accent-hover); }
.btn:active { transform: scale(0.98); }

.copy-btn {
  background: none;
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--text-muted);
  font-size: 0.78rem;
  padding: 4px 10px;
  cursor: pointer;
  transition: color 0.15s, border-color 0.15s;
}

.copy-btn:hover { color: var(--text); border-color: var(--accent); }

/* ── Result ── */
.result-section {
  margin-top: 24px;
  display: none;
}

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

.result-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 10px;
}

.result-label {
  font-size: 0.8rem;
  color: var(--text-muted);
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.result-box {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 14px 16px;
  font-size: 0.92rem;
  line-height: 1.7;
  word-break: break-all;
  color: var(--result-color);
  min-height: 56px;
}

.meta {
  margin-top: 8px;
  font-size: 0.78rem;
  color: var(--text-dim);
}

.error {
  color: var(--error-color);
  font-size: 0.85rem;
  margin-top: 8px;
  display: none;
}

.error.visible { display: block; }

/* ── Mobile ── */
@media (max-width: 480px) {
  .nav {
    padding: 12px 16px;
    gap: 10px;
  }

  .tool-body {
    padding: 20px 12px;
    align-items: flex-start;
    min-height: calc(100vh - 49px);
  }

  .card {
    padding: 20px 16px;
    border-radius: 12px;
  }

  .card h1 {
    font-size: 1.15rem;
    margin-bottom: 20px;
  }

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

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

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

  input[type="number"], select {
    font-size: 1rem;  /* prevent iOS zoom */
    padding: 11px 12px;
  }

  .btn {
    padding: 14px;
    font-size: 1rem;
  }
}