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

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

html {
  font-size: 16px;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Microsoft YaHei", "Segoe UI", sans-serif;
  background: #f5f7fa;
  color: #1f2937;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

main {
  flex: 1;
  display: flex;
  justify-content: center;
  align-items: flex-start;
  padding-top: 40px;
  padding-bottom: 40px;
}

div#app {
  width: 100%;
  max-width: none;
  padding: 0 16px;
  display: flex;
  flex-direction: column;
  align-items: center;
}

#bmi-card {
  width: 100%;
  max-width: 480px;
  background: #ffffff;
  border-radius: 16px;
  box-shadow: 0 4px 24px rgba(0, 0, 0, 0.06), 0 1px 4px rgba(0, 0, 0, 0.04);
  padding: 32px;
}

#bmi-title {
  font-size: 1.75rem;
  font-weight: 700;
  text-align: center;
  margin: 0 0 8px 0;
  color: #111827;
}

#bmi-subtitle {
  font-size: 0.875rem;
  text-align: center;
  margin: 0 0 24px 0;
  color: #6b7280;
}

#standard-switch {
  display: flex;
  gap: 8px;
  margin-bottom: 24px;
}

.standard-btn {
  flex: 1;
  padding: 10px 16px;
  border: 2px solid #e5e7eb;
  border-radius: 10px;
  background: #ffffff;
  color: #6b7280;
  font-size: 0.875rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s ease;
  font-family: inherit;
}

.standard-btn:hover {
  border-color: #10B981;
  color: #10B981;
}

.standard-btn.active {
  background: #10B981;
  border-color: #10B981;
  color: #ffffff;
}

#input-group {
  display: flex;
  flex-direction: column;
  gap: 16px;
  margin-bottom: 20px;
}

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

.input-item label {
  font-size: 0.875rem;
  font-weight: 600;
  color: #374151;
}

.input-item input {
  padding: 12px 16px;
  border: 2px solid #e5e7eb;
  border-radius: 10px;
  font-size: 1rem;
  font-family: inherit;
  color: #1f2937;
  background: #f9fafb;
  transition: border-color 0.2s ease, background 0.2s ease;
  outline: none;
  -moz-appearance: textfield;
}

.input-item input::-webkit-outer-spin-button,
.input-item input::-webkit-inner-spin-button {
  -webkit-appearance: none;
  margin: 0;
}

.input-item input:focus {
  border-color: #10B981;
  background: #ffffff;
}

.input-item input.error {
  border-color: #EF4444;
  background: #fef2f2;
}

.error-text {
  font-size: 0.75rem;
  color: #EF4444;
  min-height: 0;
}

#calc-btn {
  width: 100%;
  padding: 14px 24px;
  background: #10B981;
  color: #ffffff;
  border: none;
  border-radius: 10px;
  font-size: 1.125rem;
  font-weight: 700;
  font-family: inherit;
  cursor: pointer;
  transition: background 0.2s ease, transform 0.1s ease;
  margin-bottom: 24px;
}

#calc-btn:hover {
  background: #059669;
}

#calc-btn:active {
  transform: scale(0.98);
}

#result-area {
  padding: 24px 0 0 0;
  border-top: 1px solid #f3f4f6;
  opacity: 1;
  transform: translateY(0);
  transition: opacity 0.3s ease, transform 0.3s ease;
}

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

#result-area.fade-in {
  opacity: 0;
  transform: translateY(10px);
  animation: fadeInUp 0.3s ease forwards;
}

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

#bmi-value-area {
  text-align: center;
  margin-bottom: 12px;
}

#bmi-label {
  display: block;
  font-size: 0.875rem;
  color: #6b7280;
  margin-bottom: 4px;
}

#bmi-value {
  display: block;
  font-size: 3rem;
  font-weight: 800;
  color: #111827;
  line-height: 1.2;
}

#bmi-category {
  text-align: center;
  font-size: 1.125rem;
  font-weight: 700;
  padding: 6px 20px;
  border-radius: 20px;
  display: inline-block;
  margin: 0 auto 20px;
  width: fit-content;
}

.category-thin {
  background: #eff6ff;
  color: #3B82F6;
}

.category-normal {
  background: #ecfdf5;
  color: #10B981;
}

.category-overweight {
  background: #fffbeb;
  color: #F59E0B;
}

.category-obese {
  background: #fef2f2;
  color: #EF4444;
}

#bmi-progress-bar {
  margin-bottom: 20px;
}

#bmi-progress-track {
  position: relative;
  height: 12px;
  background: linear-gradient(to right, #3B82F6 0%, #3B82F6 25%, #10B981 25%, #10B981 50%, #F59E0B 50%, #F59E0B 75%, #EF4444 75%, #EF4444 100%);
  border-radius: 6px;
  overflow: visible;
  margin-bottom: 8px;
}

#bmi-progress-indicator {
  position: absolute;
  top: -4px;
  width: 20px;
  height: 20px;
  background: #ffffff;
  border: 3px solid #10B981;
  border-radius: 50%;
  transform: translateX(-50%);
  transition: left 0.5s ease, border-color 0.5s ease;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.12);
  z-index: 2;
}

#bmi-progress-labels {
  display: flex;
  justify-content: space-between;
  font-size: 0.75rem;
  color: #6b7280;
}

.label-thin { color: #3B82F6; }
.label-normal { color: #10B981; }
.label-overweight { color: #F59E0B; }
.label-obese { color: #EF4444; }

#bmi-advice {
  padding: 16px;
  background: #f9fafb;
  border-radius: 10px;
  font-size: 0.875rem;
  color: #4b5563;
  line-height: 1.6;
  text-align: center;
}

#bmi-intro {
  width: 100%;
  max-width: 480px;
  margin-top: 24px;
  padding: 28px 32px;
  background: #ffffff;
  border-radius: 16px;
  box-shadow: 0 4px 24px rgba(0, 0, 0, 0.06), 0 1px 4px rgba(0, 0, 0, 0.04);
}

#bmi-intro h2 {
  font-size: 1.25rem;
  font-weight: 700;
  color: #111827;
  margin: 0 0 12px 0;
}

#bmi-intro p {
  font-size: 0.9rem;
  color: #4b5563;
  line-height: 1.75;
  margin: 0;
}

#bmi-scenarios {
  width: 100%;
  max-width: 480px;
  margin-top: 24px;
  padding: 28px 32px;
  background: #ffffff;
  border-radius: 16px;
  box-shadow: 0 4px 24px rgba(0, 0, 0, 0.06), 0 1px 4px rgba(0, 0, 0, 0.04);
}

#bmi-scenarios h2 {
  font-size: 1.25rem;
  font-weight: 700;
  color: #111827;
  margin: 0 0 20px 0;
}

.scenario-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
}

.scenario-item {
  padding: 16px;
  background: #f9fafb;
  border-radius: 12px;
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.scenario-item:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
}

.scenario-icon {
  font-size: 1.75rem;
  margin-bottom: 8px;
}

.scenario-item h3 {
  font-size: 0.95rem;
  font-weight: 700;
  color: #111827;
  margin: 0 0 6px 0;
}

.scenario-item p {
  font-size: 0.8rem;
  color: #6b7280;
  line-height: 1.6;
  margin: 0;
}

footer {
  padding: 0;
  margin: 0;
}

.page-info {
  text-align: center;
  padding: 16px;
  font-size: 0.75rem;
  color: #9ca3af;
}

.page-info a {
  color: #10B981;
  text-decoration: none;
}

.page-info a:hover {
  text-decoration: underline;
}

@media (max-width: 767px) {
  main {
    padding-top: 20px;
    padding-bottom: 20px;
  }

  #bmi-card {
    padding: 24px 20px;
  }

  #bmi-title {
    font-size: 1.375rem;
  }

  #bmi-value {
    font-size: 2.5rem;
  }

  .standard-btn {
    font-size: 0.8rem;
    padding: 8px 12px;
  }

  #calc-btn {
    font-size: 1rem;
    padding: 12px 20px;
  }

  #bmi-intro,
  #bmi-scenarios {
    padding: 24px 20px;
  }

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