:root {
  --bg: #f4f6f9;
  --card: #ffffff;
  --text: #1a2332;
  --muted: #5c6b7a;
  --border: #d8e0ea;
  --primary: #1f6feb;
  --primary-hover: #1558c0;
  --danger: #c62828;
  --danger-bg: #fdecea;
  --shadow: 0 8px 24px rgba(26, 35, 50, 0.08);
  --radius: 12px;
  --font: "Segoe UI", system-ui, -apple-system, sans-serif;
}

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

body {
  margin: 0;
  font-family: var(--font);
  background: linear-gradient(160deg, #eef3fb 0%, var(--bg) 45%, #f8fafc 100%);
  color: var(--text);
  line-height: 1.5;
  min-height: 100vh;
}

.app {
  max-width: 1100px;
  margin: 0 auto;
  padding: 2rem 1.25rem 3rem;
}

.header {
  text-align: center;
  margin-bottom: 1.75rem;
}

.header h1 {
  margin: 0 0 0.5rem;
  font-size: clamp(1.5rem, 3vw, 2rem);
  font-weight: 700;
}

.subtitle {
  margin: 0;
  color: var(--muted);
}

.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.controls {
  padding: 1.25rem 1.5rem;
  margin-bottom: 1.25rem;
}

.control-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.75rem 1rem;
}

.control-row label {
  font-weight: 600;
}

.checkbox-label {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  font-weight: 600;
  cursor: pointer;
}

.control-hint {
  margin: 0;
  width: 100%;
  font-size: 0.9rem;
  color: var(--muted, #666);
}

.control-hint code {
  font-size: 0.85em;
}

.success-hint {
  color: var(--primary, #1a6b4a);
}

select {
  min-width: 220px;
  padding: 0.6rem 0.85rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  font-size: 1rem;
  background: #fff;
}

.form-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin-bottom: 1.25rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.65rem 1.25rem;
  border: none;
  border-radius: 8px;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s ease, opacity 0.15s ease;
}

.btn:disabled {
  opacity: 0.65;
  cursor: not-allowed;
}

.btn-primary {
  background: var(--primary);
  color: #fff;
}

.btn-primary:hover:not(:disabled) {
  background: var(--primary-hover);
}

.btn-secondary {
  background: #e8eef6;
  color: var(--text);
}

.btn-secondary:hover:not(:disabled) {
  background: #d9e3f0;
}

.spinner {
  width: 1rem;
  height: 1rem;
  border: 2px solid rgba(255, 255, 255, 0.35);
  border-top-color: #fff;
  border-radius: 50%;
  animation: spin 0.7s linear infinite;
}

.hidden {
  display: none !important;
}

@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}

.error-banner {
  background: var(--danger-bg);
  color: var(--danger);
  border: 1px solid #f5c2c0;
  border-radius: 8px;
  padding: 0.85rem 1rem;
  margin-bottom: 1rem;
  font-weight: 500;
}

.fields-grid {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.field-row {
  padding: 1rem 1.25rem;
}

.field-pair-header {
  padding: 0 1.25rem;
  margin-bottom: -0.25rem;
}

.column-label {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.03em;
}

.field-pair-header .arrow {
  padding-top: 0;
}

.field-label {
  font-weight: 600;
  margin-bottom: 0.75rem;
}

.field-pair {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 0.75rem;
  align-items: start;
}

.field-group {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
}

.output-group {
  position: relative;
}

textarea,
.input-select {
  width: 100%;
  resize: vertical;
  min-height: 3.25rem;
  padding: 0.7rem 0.85rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  font: inherit;
  background: #fff;
}

.input-select {
  resize: none;
  min-height: auto;
  cursor: pointer;
}

.output-field {
  background: #f8fbff;
  padding-right: 4.5rem;
}

.char-count {
  font-size: 0.8rem;
  color: var(--muted);
  text-align: right;
}

.arrow {
  align-self: center;
  font-size: 1.4rem;
  color: var(--primary);
  font-weight: 700;
  padding-top: 0.5rem;
}

.btn-copy {
  position: absolute;
  top: 0.45rem;
  right: 0.45rem;
  padding: 0.3rem 0.55rem;
  font-size: 0.75rem;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: #fff;
  cursor: pointer;
}

.btn-copy:hover {
  background: #eef4fc;
}

.btn-copy.copied {
  background: #e6f4ea;
  border-color: #a8dab5;
  color: #1e7e34;
}

.footer {
  margin-top: 2rem;
  text-align: center;
  color: var(--muted);
  font-size: 0.9rem;
}

@media (max-width: 768px) {
  .app {
    padding: 1.25rem 1rem 2rem;
  }

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

  .arrow {
    display: none;
  }

  select {
    width: 100%;
  }
}