:root {
      --primary: #0f172a;
      --accent: #3b82f6;
      --accent-light: #60a5fa;
      --bg: #f8fafc;
      --card-bg: #ffffff;
      --text: #1e293b;
      --text-light: #64748b;
      --border: #e2e8f0;
      --success: #10b981;
      --warning: #f59e0b;
      --danger: #ef4444;
      --shadow: 0 1px 3px 0 rgba(0,0,0,0.1), 0 1px 2px -1px rgba(0,0,0,0.1);
      --shadow-lg: 0 10px 15px -3px rgba(0,0,0,0.1), 0 4px 6px -4px rgba(0,0,0,0.1);
      --radius: 16px;
      --radius-sm: 10px;
      --nav-height: 64px;
    }
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
      background: var(--bg);
      color: var(--text);
      line-height: 1.6;
      -webkit-font-smoothing: antialiased;
    }

    /* Nav */
    .nav-bar {
      position: fixed;
      top: 0; left: 0; right: 0;
      height: var(--nav-height);
      background: rgba(255,255,255,0.95);
      backdrop-filter: blur(10px);
      border-bottom: 1px solid var(--border);
      z-index: 1000;
    }
    .nav-inner {
      max-width: 1200px;
      margin: 0 auto;
      height: 100%;
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 0 1.5rem;
    }
    .nav-logo {
      display: flex;
      align-items: center;
      gap: 0.5rem;
      font-weight: 800;
      font-size: 1.25rem;
      color: var(--primary);
      text-decoration: none;
    }
    .nav-logo svg { width: 24px; height: 24px; stroke: var(--accent); }
    .nav-links { display: flex; gap: 2rem; }
    .nav-links a {
      text-decoration: none;
      color: var(--text-light);
      font-weight: 500;
      font-size: 0.95rem;
      transition: color 0.2s;
    }
    .nav-links a:hover, .nav-links a.active { color: var(--accent); }
    .nav-toggle { display: none; }

    /* Header */
    header {
      text-align: center;
      padding: calc(var(--nav-height) + 3rem) 1.5rem 2rem;
      max-width: 800px;
      margin: 0 auto;
    }
    header h1 {
      font-size: 2rem;
      font-weight: 800;
      margin-bottom: 0.5rem;
      color: var(--primary);
      letter-spacing: -0.02em;
    }
    header p { color: var(--text-light); font-size: 1.05rem; }

    /* Main Layout */
    main { max-width: 1200px; margin: 0 auto; padding: 0 1.5rem 3rem; }
    .calculator-layout {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 2rem;
      align-items: start;
      margin-bottom: 3rem;
    }
    .calc-panel {
      position: sticky;
      top: calc(var(--nav-height) + 1.5rem);
      align-self: start;
    }
    .calculator-card {
      background: var(--card-bg);
      border-radius: var(--radius);
      padding: 2rem;
      box-shadow: var(--shadow-lg);
      border: 1px solid var(--border);
    }
    .intro-text {
      font-size: 0.95rem;
      color: var(--text-light);
      margin-bottom: 1.5rem;
      line-height: 1.7;
    }
    .intro-text strong { color: var(--text); }

    /* Result Panel */
    .result-panel { min-height: 200px; }
    .result-placeholder {
      background: var(--card-bg);
      border-radius: var(--radius);
      padding: 3rem 2rem;
      box-shadow: var(--shadow);
      text-align: center;
      color: var(--text-light);
      border: 2px dashed var(--border);
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 300px;
    }

    .result-placeholder p { margin: 0.25rem 0; font-size: 0.95rem; }
    .result-placeholder p:last-child { font-size: 0.85rem; opacity: 0.7; }

    #results {
      display: none;
      background: var(--card-bg);
      border-radius: var(--radius);
      padding: 2rem;
      box-shadow: var(--shadow-lg);
      border: 1px solid var(--border);
      opacity: 0;
      transform: translateY(12px);
      transition: opacity 0.5s ease, transform 0.5s ease;
    }
    #results.visible {
      display: block;
      opacity: 1;
      transform: translateY(0);
    }

    /* Form */
    .form-section { margin-bottom: 1.75rem; }
    .form-section:last-of-type { margin-bottom: 1rem; }
    .form-section h2 {
      font-size: 1.05rem;
      font-weight: 700;
      margin-bottom: 1rem;
      display: flex;
      align-items: center;
      gap: 0.5rem;
      color: var(--primary);
    }
    .step-num {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      width: 28px;
      height: 28px;
      background: var(--accent);
      color: white;
      border-radius: 50%;
      font-size: 0.8rem;
      font-weight: 700;
      flex-shrink: 0;
    }

    /* Cards */
    .formula-cards, .activity-cards {
      display: grid;
      grid-template-columns: repeat(auto-fit, minmax(130px, 1fr));
      gap: 0.75rem;
    }
    .formula-card, .activity-card {
      border: 2px solid var(--border);
      border-radius: var(--radius-sm);
      padding: 1rem;
      cursor: pointer;
      transition: all 0.2s;
      position: relative;
      background: white;
      user-select: none;
    }
    .formula-card:hover, .activity-card:hover {
      border-color: var(--accent-light);
      transform: translateY(-2px);
      box-shadow: 0 4px 12px rgba(59,130,246,0.08);
    }
    .formula-card.selected, .activity-card.selected {
      border-color: var(--accent);
      background: #eff6ff;
      box-shadow: 0 0 0 3px rgba(59,130,246,0.12);
    }
    .check-mark {
      position: absolute;
      top: 8px; right: 8px;
      width: 20px; height: 20px;
      background: var(--accent);
      color: white;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 0.7rem;
      opacity: 0;
      transition: opacity 0.2s;
    }
    .formula-card.selected .check-mark { opacity: 1; }
    .card-icon { font-size: 1.5rem; margin-bottom: 0.5rem; }
    .formula-card h3 { font-size: 0.9rem; margin-bottom: 0.25rem; color: var(--text); }
    .formula-card p { font-size: 0.78rem; color: var(--text-light); line-height: 1.4; }


    .activity-card .act-label { font-weight: 700; margin-bottom: 0.25rem; font-size: 0.9rem; }
    .activity-card .act-desc { font-size: 0.78rem; color: var(--text-light); line-height: 1.4; }

    .info-box {
      margin-top: 1rem;
      padding: 1rem;
      background: #f8fafc;
      border-radius: var(--radius-sm);
      border-left: 4px solid var(--accent);
      font-size: 0.9rem;
      color: var(--text-light);
      line-height: 1.5;
    }

    /* Inputs */
    .form-grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 1rem;
    }
    .form-group.hidden { display: none !important; }
    .form-group {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}
.form-group label {
  flex-shrink: 0;        /* label 不压缩 */
  min-width: 4.5em;      /* 最小宽度，对齐用 */
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-light);
}
.form-group input,
.form-group select {
  flex: 1;               /* input 占满剩余空间 */
  padding: 0.6rem 0.75rem;
  border: 2px solid var(--border);
  border-radius: var(--radius-sm);
  font-size: 1rem;
  background: white;
  width: 100%;
}
    .form-group input:focus, .form-group select:focus {
      outline: none;
      border-color: var(--accent);
      box-shadow: 0 0 0 3px rgba(59,130,246,0.08);
    }
    .form-group.error input { border-color: var(--danger); }

    .inline-help {
      color: var(--accent);
      text-decoration: none;
      font-size: 0.75rem;
      margin-left: 0.25rem;
      font-weight: 600;
    }
    .inline-help:hover { text-decoration: underline; }

    button[type="submit"] {
      width: 100%;
      padding: 1rem;
      background: var(--accent);
      color: white;
      border: none;
      border-radius: var(--radius-sm);
      font-size: 1.1rem;
      font-weight: 700;
      cursor: pointer;
      transition: all 0.2s;
      margin-top: 0.5rem;
      letter-spacing: 0.02em;
    }
    button[type="submit"]:hover {
      background: #2563eb;
      transform: translateY(-1px);
      box-shadow: 0 8px 20px rgba(59,130,246,0.25);
    }
    button[type="submit"]:active { transform: translateY(0); }

    /* Results */
    .result-hero {
      text-align: center;
      padding-bottom: 1.5rem;
      border-bottom: 1px solid var(--border);
      margin-bottom: 1.5rem;
    }
    .hero-label { font-size: 0.9rem; color: var(--text-light); margin-bottom: 0.5rem; font-weight: 500; }
    .hero-number {
      font-size: 3.5rem;
      font-weight: 800;
      color: var(--accent);
      line-height: 1;
      letter-spacing: -0.03em;
    }
    .hero-unit { font-size: 0.9rem; color: var(--text-light); margin-top: 0.35rem; font-weight: 500; }
    .hero-formula {
      font-size: 0.8rem;
      color: var(--text-light);
      margin-top: 0.75rem;
      background: var(--bg);
      display: inline-block;
      padding: 0.4rem 1rem;
      border-radius: 20px;
      font-weight: 500;
    }

    .breakdown-grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 1rem;
      margin-top: 1.5rem;
    }
    .breakdown-item {
      background: var(--bg);
      padding: 1rem;
      border-radius: var(--radius-sm);
      text-align: center;
    }
    .bd-label { font-size: 0.8rem; color: var(--text-light); margin-bottom: 0.35rem; font-weight: 500; }
    .bd-value { font-size: 1.5rem; font-weight: 800; color: var(--text); }
    .bd-unit { font-size: 0.75rem; color: var(--text-light); font-weight: 500; }

    .diet-section-title {
      font-size: 1.1rem;
      font-weight: 800;
      margin-bottom: 1.25rem;
      text-align: center;
      color: var(--primary);
    }
    .diet-grid {
      display: grid;
      grid-template-columns: repeat(3, 1fr);
      gap: 0.75rem;
    }
    .diet-card {
      background: var(--bg);
      border-radius: var(--radius-sm);
      padding: 1.5rem 1rem;
      text-align: center;
      transition: transform 0.2s, box-shadow 0.2s;
      border: 1px solid var(--border);
    }
    .diet-card:hover { transform: translateY(-4px); box-shadow: 0 8px 16px rgba(0,0,0,0.06); }
    .diet-card.cut { border-top: 3px solid var(--success); }
    .diet-card.maintain { border-top: 3px solid var(--accent); }
    .diet-card.bulk { border-top: 3px solid var(--warning); }
    .diet-card h4 { font-size: 0.9rem; margin-bottom: 0.5rem; color: var(--text); }
    .cal { font-size: 1.5rem; font-weight: 800; color: var(--primary); }
    .cal-unit { font-size: 0.75rem; color: var(--text-light); font-weight: 500; }
    .reason {
      font-size: 0.75rem;
      color: var(--text-light);
      margin-top: 0.75rem;
      line-height: 1.5;
    }

    /* FAQ Accordion */
    .faq-section { margin-top: 1rem; }
    .faq-section > h2 {
      font-size: 1.5rem;
      font-weight: 800;
      margin-bottom: 1.5rem;
      text-align: center;
      color: var(--primary);
    }
    details.faq-item {
      background: var(--card-bg);
      border-radius: var(--radius-sm);
      margin-bottom: 1rem;
      box-shadow: var(--shadow);
      overflow: hidden;
      border: 1px solid var(--border);
    }
    details.faq-item summary {
      padding: 1.25rem 1.5rem;
      font-weight: 700;
      cursor: pointer;
      list-style: none;
      display: flex;
      align-items: center;
      justify-content: space-between;
      transition: background 0.2s;
      font-size: 1rem;
      color: var(--text);
      line-height: 1.4;
    }
    details.faq-item summary::-webkit-details-marker { display: none; }
    details.faq-item summary::after {
      content: '+';
      font-size: 1.5rem;
      color: var(--accent);
      font-weight: 400;
      transition: transform 0.3s;
      flex-shrink: 0;
      margin-left: 1rem;
    }
    details.faq-item[open] summary::after { content: '−'; }
    details.faq-item summary:hover { background: #f8fafc; }
    details.faq-item .faq-content {
      padding: 0 1.5rem 1.5rem;
      animation: fadeIn 0.35s ease;
    }
    @keyframes fadeIn { from { opacity: 0; transform: translateY(-4px); } to { opacity: 1; transform: translateY(0); } }

    .faq-content h4 {
      font-size: 1rem;
      margin: 1.25rem 0 0.75rem;
      color: var(--primary);
      font-weight: 700;
    }
    .faq-content h4:first-child { margin-top: 0.5rem; }
    .faq-content p { margin-bottom: 0.75rem; font-size: 0.95rem; color: var(--text-light); line-height: 1.7; }
    .faq-content ul, .faq-content ol {
      margin: 0.75rem 0;
      padding-left: 1.25rem;
      color: var(--text-light);
    }
    .faq-content li { margin-bottom: 0.5rem; font-size: 0.95rem; line-height: 1.7; }
    .faq-content strong { color: var(--text); }
    .faq-content code {
      background: #f1f5f9;
      padding: 0.2rem 0.4rem;
      border-radius: 4px;
      font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
      font-size: 0.85em;
      color: var(--accent);
    }

    .comparison-table {
      width: 100%;
      border-collapse: collapse;
      margin: 1rem 0;
      font-size: 0.9rem;
    }
    .comparison-table th, .comparison-table td {
      border: 1px solid var(--border);
      padding: 0.65rem 0.75rem;
      text-align: left;
      line-height: 1.5;
    }
    .comparison-table th {
      background: var(--bg);
      font-weight: 700;
      font-size: 0.82rem;
      color: var(--text);
    }
    .comparison-table td { color: var(--text-light); font-size: 0.88rem; }
    .comparison-table tr:nth-child(even) { background: #f8fafc; }

    .tip-box {
      background: #eff6ff;
      border-left: 4px solid var(--accent);
      padding: 1rem;
      border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
      margin-top: 1rem;
      display: flex;
      gap: 0.75rem;
      align-items: flex-start;
    }
    .tip-icon { font-size: 1.25rem; flex-shrink: 0; line-height: 1; }
    .tip-box div { font-size: 0.9rem; color: var(--text-light); line-height: 1.6; }
    .tip-box div strong { color: var(--text); }

    .method-tag {
      display: inline-block;
      padding: 0.15rem 0.5rem;
      border-radius: 4px;
      font-size: 0.75rem;
      font-weight: 700;
      margin-left: 0.5rem;
      vertical-align: middle;
    }
    .method-tag.gold { background: #fef3c7; color: #92400e; }
    .method-tag.good { background: #d1fae5; color: #065f46; }
    .method-tag.okay { background: #dbeafe; color: #1e40af; }
    .method-tag.rough { background: #f3f4f6; color: #4b5563; }

    .faq-lead { font-size: 0.95rem; color: var(--text-light); margin-bottom: 1rem; line-height: 1.7; }
    .formula-note {
      font-size: 0.85rem;
      color: var(--text-light);
      margin: 0.5rem 0 1rem;
      line-height: 1.6;
      font-style: italic;
    }

    /* Footer */
    footer {
      text-align: center;
      padding: 2.5rem 1.5rem;
      color: var(--text-light);
      font-size: 0.85rem;
      border-top: 1px solid var(--border);
      margin-top: 1rem;
      background: white;
    }

    /* Back to top */
    #backToTop {
      position: fixed;
      bottom: 2rem;
      right: 2rem;
      width: 48px;
      height: 48px;
      border-radius: 50%;
      background: var(--accent);
      color: white;
      border: none;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      opacity: 0;
      visibility: hidden;
      transition: all 0.3s;
      box-shadow: 0 4px 12px rgba(59,130,246,0.3);
      z-index: 999;
    }
    #backToTop.visible { opacity: 1; visibility: visible; }
    #backToTop:hover { transform: translateY(-2px); background: #2563eb; }
    #backToTop svg { width: 24px; height: 24px; }

    /* Mobile Nav */
    .nav-mobile,
.nav-overlay {
  display: none;
}

@media (max-width: 640px) {
  .nav-links { display: none; }
  
  .nav-mobile {
    display: block; /* 覆盖上面的 none */
    position: fixed;
    top: 0; right: 0;
    width: 280px;
    height: 100vh;
    background: white;
    padding: 1.5rem;
    transform: translateX(100%);
    transition: transform 0.3s ease;
    z-index: 1001;
    box-shadow: -4px 0 20px rgba(0,0,0,0.1);
  }
  .nav-mobile.open {
    transform: translateX(0);
  }
  
  .nav-overlay {
    display: block; /* 覆盖上面的 none */
    position: fixed;
    inset: 0;
    background: rgba(15,23,42,0.4);
    opacity: 0;
    visibility: hidden;
    transition: 0.3s;
    z-index: 1000;
  }
  .nav-overlay.open {
    opacity: 1;
    visibility: visible;
  }
    @media (max-width: 640px) {
      .nav-links { display: none; }
      .nav-toggle {
        display: flex;
        flex-direction: column;
        gap: 5px;
        background: none;
        border: none;
        cursor: pointer;
        padding: 0.5rem;
      }
      .nav-toggle span {
        display: block;
        width: 24px;
        height: 2px;
        background: var(--text);
        transition: 0.3s;
      }
      .nav-mobile {
        position: fixed;
        top: 0; right: 0;
        width: 280px;
        height: 100vh;
        background: white;
        padding: 1.5rem;
        transform: translateX(100%);
        transition: transform 0.3s ease;
        z-index: 1001;
        box-shadow: -4px 0 20px rgba(0,0,0,0.1);
      }
      .nav-mobile.open { transform: translateX(0); }
      .nav-overlay {
        position: fixed;
        inset: 0;
        background: rgba(15,23,42,0.4);
        opacity: 0;
        visibility: hidden;
        transition: 0.3s;
        z-index: 1000;
      }
      .nav-overlay.open { opacity: 1; visibility: visible; }
      .nav-mobile-label {
        font-size: 0.7rem;
        text-transform: uppercase;
        letter-spacing: 1.5px;
        color: var(--text-light);
        margin-bottom: 1rem;
        font-weight: 700;
      }
      .nav-mobile a {
        display: block;
        padding: 0.875rem 0;
        color: var(--text);
        text-decoration: none;
        border-bottom: 1px solid var(--border);
        font-weight: 500;
        font-size: 1rem;
      }
      .nav-mobile a.active { color: var(--accent); }
    }

    /* Responsive */
    @media (max-width: 900px) {
      .calculator-layout {
        grid-template-columns: 1fr;
        gap: 1.5rem;
      }
      .calc-panel {
        position: relative;
        top: 0;
      }
      .diet-grid { grid-template-columns: 1fr; }
      .breakdown-grid { grid-template-columns: 1fr 1fr; }
      .formula-cards { grid-template-columns: 1fr; }
      .activity-cards { grid-template-columns: 1fr 1fr; }
      header h1 { font-size: 1.5rem; }
      .hero-number { font-size: 2.5rem; }
      .result-placeholder { min-height: 200px; }
    }

    @media (max-width: 480px) {
      .form-grid { grid-template-columns: 1fr; }
      .activity-cards { grid-template-columns: 1fr; }
      .breakdown-grid { grid-template-columns: 1fr; }
      .calculator-card, #results { padding: 1.25rem; }
      main { padding: 0 1rem 2rem; }
      .diet-grid { grid-template-columns: 1fr; }
      .comparison-table { font-size: 0.82rem; }
      .comparison-table th, .comparison-table td { padding: 0.5rem; }
      header { padding-top: calc(var(--nav-height) + 2rem); }
      header h1 { font-size: 1.35rem; }
    }

    /* Print */
    @media print {
      .nav-bar, .nav-toggle, #backToTop, .faq-section, .result-placeholder { display: none !important; }
      .calculator-layout { grid-template-columns: 1fr; }
      #results { display: block !important; opacity: 1 !important; page-break-inside: avoid; }
    }
}


/* 菜单内显式关闭按钮 */
.nav-mobile-close {
  display: none;
}
@media (max-width: 640px) {
  .nav-mobile-close {
    display: flex;
    align-items: center;
    justify-content: center;
    position: absolute;
    top: calc(var(--nav-height) / 2 - 16px);
    right: 1rem;
    width: 32px;
    height: 32px;
    border-radius: 50%;
    border: none;
    background: var(--bg);
    color: var(--text);
    font-size: 1.25rem;
    line-height: 1;
    cursor: pointer;
    z-index: 1003;
    transition: background 0.2s, color 0.2s;
  }
  .nav-mobile-close:hover {
    background: var(--accent);
    color: white;
  }
}