html, body, main, header, footer {
  padding: 0;
  margin: 0;
}

#app {
  max-width: 720px;
  margin: 0 auto;
  padding: 24px 16px;
}

#app-title {
  text-align: center;
  font-size: 28px;
  color: #1a6fb5;
  margin-bottom: 8px;
}

#app-subtitle {
  text-align: center;
  font-size: 15px;
  color: #666;
  margin-bottom: 32px;
}

.card {
  background: #fff;
  border-radius: 12px;
  box-shadow: 0 2px 12px rgba(0, 0, 0, 0.08);
  padding: 24px;
  margin-bottom: 20px;
}

.card h3 {
  font-size: 18px;
  color: #333;
  margin-bottom: 16px;
  padding-bottom: 10px;
  border-bottom: 2px solid #e8f0f8;
}

.input-group {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 16px;
}

#gas-usage {
  flex: 1;
  height: 44px;
  font-size: 18px;
  padding: 0 14px;
  border: 2px solid #d0d7de;
  border-radius: 8px;
  outline: none;
  transition: border-color 0.2s;
}

#gas-usage:focus {
  border-color: #1a6fb5;
}

#gas-unit {
  font-size: 16px;
  color: #555;
  min-width: 24px;
}

.preset-group {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
}

#preset-label {
  font-size: 14px;
  color: #666;
}

.preset-btn {
  padding: 6px 14px;
  font-size: 13px;
  color: #1a6fb5;
  background: #e8f4fc;
  border: 1px solid #b8d8f0;
  border-radius: 6px;
  cursor: pointer;
  transition: all 0.2s;
}

.preset-btn:hover {
  background: #1a6fb5;
  color: #fff;
  border-color: #1a6fb5;
}

#tier-list {
  display: flex;
  flex-direction: column;
  gap: 12px;
  margin-bottom: 16px;
}

.tier-item {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 12px 14px;
  background: #f7f9fb;
  border-radius: 8px;
  flex-wrap: wrap;
}

.tier-label {
  font-size: 14px;
  font-weight: 600;
  color: #1a6fb5;
  min-width: 48px;
}

.tier-range-label {
  font-size: 13px;
  color: #888;
}

.tier-limit, .tier-price, .tier-price-only {
  width: 72px;
  height: 36px;
  font-size: 14px;
  padding: 0 8px;
  border: 1px solid #d0d7de;
  border-radius: 6px;
  outline: none;
  text-align: center;
  transition: border-color 0.2s;
}

.tier-limit:focus, .tier-price:focus, .tier-price-only:focus {
  border-color: #1a6fb5;
}

.tier-unit {
  font-size: 13px;
  color: #666;
}

#tier-actions {
  display: flex;
  gap: 10px;
}

.btn-secondary {
  padding: 8px 16px;
  font-size: 13px;
  color: #555;
  background: #f0f0f0;
  border: 1px solid #ddd;
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s;
}

.btn-secondary:hover {
  background: #e0e0e0;
  color: #333;
}

.result-placeholder {
  text-align: center;
  padding: 40px 20px;
}

#result-placeholder-text {
  font-size: 15px;
  color: #aaa;
}

.result-hidden {
  display: none !important;
}

.total-display {
  text-align: center;
  padding: 24px 0;
  background: linear-gradient(135deg, #e8f4fc, #f0f7ff);
  border-radius: 10px;
  margin-bottom: 20px;
}

#total-label {
  display: block;
  font-size: 15px;
  color: #666;
  margin-bottom: 8px;
}

#total-value {
  font-size: 42px;
  font-weight: 700;
  color: #1a6fb5;
}

#total-unit {
  font-size: 20px;
  color: #1a6fb5;
  margin-left: 4px;
}

#tier-details-title {
  font-size: 15px;
  color: #444;
  margin-bottom: 12px;
}

#tier-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
}

#tier-table thead th {
  background: #f7f9fb;
  padding: 10px 8px;
  text-align: center;
  font-weight: 600;
  color: #555;
  border-bottom: 2px solid #e0e5ea;
}

#tier-table tbody td {
  padding: 10px 8px;
  text-align: center;
  color: #333;
  border-bottom: 1px solid #f0f2f5;
}

#tier-table tbody tr:last-child td {
  border-bottom: none;
}

#action-section {
  text-align: center;
  margin-top: 12px;
}

.btn-primary {
  padding: 12px 40px;
  font-size: 16px;
  color: #fff;
  background: #1a6fb5;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.2s;
}

.btn-primary:hover {
  background: #155a8f;
}

#features, #scenarios, #FAQ {
  max-width: 720px;
  margin: 0 auto;
  padding: 24px 16px;
}

#features h2, #scenarios h2, #FAQ h2 {
  font-size: 20px;
  color: #333;
  margin-bottom: 12px;
}

#features p {
  font-size: 15px;
  color: #555;
  line-height: 1.8;
}

#scenarios ul {
  padding-left: 20px;
}

#scenarios li {
  font-size: 14px;
  color: #555;
  line-height: 2;
}

#FAQ dl {
  margin: 0;
}

#FAQ dt {
  font-size: 15px;
  font-weight: 600;
  color: #333;
  margin-top: 16px;
  margin-bottom: 6px;
}

#FAQ dd {
  font-size: 14px;
  color: #666;
  line-height: 1.7;
  margin-left: 0;
  padding-bottom: 12px;
  border-bottom: 1px dashed #e0e5ea;
}

#FAQ dd:last-of-type {
  border-bottom: none;
}

@media (max-width: 480px) {
  #app {
    padding: 16px 12px;
  }

  #app-title {
    font-size: 22px;
  }

  .card {
    padding: 16px;
  }

  #total-value {
    font-size: 32px;
  }

  .tier-item {
    flex-wrap: wrap;
    gap: 6px;
  }

  .tier-limit, .tier-price, .tier-price-only {
    width: 64px;
    height: 32px;
    font-size: 13px;
  }

  #tier-table {
    font-size: 12px;
  }

  #tier-table thead th,
  #tier-table tbody td {
    padding: 8px 4px;
  }

  .preset-btn {
    padding: 5px 10px;
    font-size: 12px;
  }
}