:root {
  --primary: #2563EB;
  --primary-light: #DBEAFE;
  --primary-dark: #1D4ED8;
  --bg: #F3F4F6;
  --card-bg: #FFFFFF;
  --text: #1F2937;
  --text-secondary: #6B7280;
  --text-muted: #9CA3AF;
  --border: #E5E7EB;
  --error: #EF4444;
  --success: #10B981;
  --radius: 16px;
  --shadow: 0 1px 3px rgba(0,0,0,0.06), 0 4px 12px rgba(0,0,0,0.04);
  --shadow-lg: 0 2px 8px rgba(0,0,0,0.08), 0 8px 24px rgba(0,0,0,0.06);
  --transition: 0.2s ease;
}

html, body {
  margin: 0;
  padding: 0;
}

* {
  box-sizing: border-box;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Microsoft YaHei", "Segoe UI", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

main {
  margin: 0;
  padding: 0;
  flex: 1;
  display: flex;
  justify-content: center;
  align-items: flex-start;
  padding: 24px 16px 40px;
}

header, footer {
  margin: 0;
  padding: 0;
}

header {
  display: flex;
  justify-content: center;
  padding: 16px 16px 0;
}

footer {
  text-align: center;
  padding: 16px;
  font-size: 13px;
  color: var(--text-muted);
}

footer a {
  color: var(--primary);
  text-decoration: none;
}

footer a:hover {
  text-decoration: underline;
}

div#app {
  width: 100%;
  max-width: 600px;
}

#calculator-card {
  background: var(--card-bg);
  border-radius: var(--radius);
  box-shadow: var(--shadow-lg);
  padding: 32px;
  width: 100%;
}

#title {
  margin: 0 0 28px;
  font-size: 24px;
  font-weight: 700;
  color: var(--text);
  text-align: center;
  letter-spacing: 0.5px;
}

#input-section {
  display: flex;
  flex-direction: column;
  gap: 20px;
  margin-bottom: 24px;
}

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

.input-group label {
  font-size: 14px;
  font-weight: 600;
  color: var(--text-secondary);
  letter-spacing: 0.3px;
}

.input-group input[type="number"] {
  width: 100%;
  padding: 10px 14px;
  border: 1.5px solid var(--border);
  border-radius: 10px;
  font-size: 16px;
  font-family: inherit;
  color: var(--text);
  background: var(--card-bg);
  transition: border-color var(--transition), box-shadow var(--transition);
  outline: none;
  -moz-appearance: textfield;
}

.input-group input[type="number"]::-webkit-outer-spin-button,
.input-group input[type="number"]::-webkit-inner-spin-button {
  -webkit-appearance: none;
  margin: 0;
}

.input-group input[type="number"]:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px var(--primary-light);
}

.input-group input[type="number"].error {
  border-color: var(--error);
}

.error-msg {
  font-size: 12px;
  color: var(--error);
  min-height: 18px;
  display: block;
}

#down-payment-options {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.dp-btn {
  flex: 1;
  min-width: 72px;
  padding: 8px 12px;
  border: 1.5px solid var(--border);
  border-radius: 10px;
  background: var(--card-bg);
  font-size: 14px;
  font-weight: 500;
  font-family: inherit;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition);
  white-space: nowrap;
}

.dp-btn:hover {
  border-color: var(--primary);
  color: var(--primary);
}

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

#custom-dp-wrapper {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-top: 4px;
}

#custom-dp-wrapper.hidden {
  display: none;
}

#custom-dp-wrapper input {
  flex: 1;
}

#custom-dp-unit {
  font-size: 16px;
  font-weight: 600;
  color: var(--text-secondary);
}

#loan-amount-display {
  background: var(--primary-light);
  border-radius: 10px;
  padding: 14px 18px;
  display: flex;
  align-items: center;
  gap: 8px;
  flex-wrap: wrap;
}

#loan-amount-label {
  font-size: 14px;
  font-weight: 600;
  color: var(--primary-dark);
}

#loan-amount-value {
  font-size: 18px;
  font-weight: 700;
  color: var(--primary);
}

#method-toggle {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 24px;
  flex-wrap: wrap;
}

#toggle-label {
  font-size: 14px;
  font-weight: 600;
  color: var(--text-secondary);
}

#toggle-buttons {
  display: flex;
  background: var(--bg);
  border-radius: 10px;
  padding: 3px;
  gap: 2px;
}

.method-btn {
  padding: 8px 20px;
  border: none;
  border-radius: 8px;
  background: transparent;
  font-size: 14px;
  font-weight: 500;
  font-family: inherit;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition);
  white-space: nowrap;
}

.method-btn:hover {
  color: var(--text);
}

.method-btn.active {
  background: var(--card-bg);
  color: var(--primary);
  box-shadow: 0 1px 2px rgba(0,0,0,0.06);
  font-weight: 600;
}

#result-section {
  margin-bottom: 24px;
}

#result-section.hidden {
  display: none;
}

#result-primary {
  display: grid;
  grid-template-columns: 1fr;
  gap: 16px;
}

.result-item {
  background: var(--bg);
  border-radius: 12px;
  padding: 20px;
  text-align: center;
  animation: fadeInUp 0.4s ease both;
}

.result-item:nth-child(1) { animation-delay: 0.05s; }
.result-item:nth-child(2) { animation-delay: 0.1s; }
.result-item:nth-child(3) { animation-delay: 0.15s; }

.result-label {
  display: block;
  font-size: 13px;
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: 6px;
  letter-spacing: 0.3px;
}

.result-value {
  display: block;
  font-size: 28px;
  font-weight: 700;
  color: var(--primary);
}

.result-sub {
  display: block;
  font-size: 13px;
  color: var(--text-muted);
  margin-top: 4px;
}

#comparison-section {
  border-top: 2px solid var(--bg);
  padding-top: 24px;
}

#comparison-section.hidden {
  display: none;
}

#comparison-title {
  font-size: 18px;
  font-weight: 700;
  color: var(--text);
  margin: 0 0 16px;
  text-align: center;
}

#comparison-cards {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}

.comp-card {
  background: var(--bg);
  border-radius: 12px;
  overflow: hidden;
  animation: fadeInUp 0.4s ease both;
}

.comp-card:nth-child(1) { animation-delay: 0.1s; }
.comp-card:nth-child(2) { animation-delay: 0.15s; }

.comp-card-header {
  background: var(--primary);
  color: #fff;
  font-size: 14px;
  font-weight: 700;
  text-align: center;
  padding: 10px;
  letter-spacing: 0.3px;
}

.comp-card-body {
  padding: 14px 16px;
}

.comp-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 8px 0;
  border-bottom: 1px solid var(--border);
}

.comp-row:last-child {
  border-bottom: none;
}

.comp-label {
  font-size: 13px;
  color: var(--text-secondary);
  font-weight: 500;
}

.comp-value {
  font-size: 14px;
  font-weight: 700;
  color: var(--text);
}

@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(12px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

#intro-section,
#scenarios-section {
  background: var(--card-bg);
  border-radius: var(--radius);
  box-shadow: var(--shadow-lg);
  padding: 32px;
  margin-top: 24px;
}

#intro-section h2,
#scenarios-section h2 {
  margin: 0 0 16px;
  font-size: 18px;
  font-weight: 700;
  color: var(--text);
  text-align: center;
}

#intro-section p {
  margin: 0;
  font-size: 15px;
  line-height: 1.8;
  color: var(--text-secondary);
}

#scenarios-section ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 16px;
}

#scenarios-section li {
  display: flex;
  align-items: flex-start;
  gap: 12px;
  padding: 16px;
  background: var(--bg);
  border-radius: 12px;
  border-left: 3px solid var(--primary);
}

#scenarios-section li strong {
  font-size: 14px;
  font-weight: 700;
  color: var(--primary);
  white-space: nowrap;
  min-width: 90px;
}

#scenarios-section li span {
  font-size: 14px;
  line-height: 1.7;
  color: var(--text-secondary);
}

@media (max-width: 767px) {
  main {
    padding: 16px 8px 32px;
  }

  #calculator-card {
    padding: 24px 20px;
    border-radius: 12px;
  }

  #title {
    font-size: 22px;
    margin-bottom: 22px;
  }

  #input-section {
    gap: 16px;
  }

  .input-group input[type="number"] {
    font-size: 15px;
    padding: 10px 12px;
  }

  #comparison-cards {
    grid-template-columns: 1fr;
  }

  .result-value {
    font-size: 24px;
  }

  #method-toggle {
    flex-direction: column;
    align-items: flex-start;
  }

  #toggle-buttons {
    width: 100%;
  }

  .method-btn {
    flex: 1;
    text-align: center;
  }

  #intro-section,
  #scenarios-section {
    padding: 24px 20px;
    border-radius: 12px;
  }

  #scenarios-section li {
    flex-direction: column;
    gap: 8px;
  }

  #scenarios-section li strong {
    white-space: normal;
    min-width: auto;
  }
}