:root {
      --calc-primary: #8b5cf6;
      --calc-primary-light: #f5f3ff;
      --calc-primary-dark: #6d28d9;
      --ink: #0f172a;
      --ink-2: #334155;
      --ink-3: #64748b;
      --white: #ffffff;
      --off: #f8fafc;
      --line: #e2e8f0;
      --line-2: #cbd5e1;
      --ease: cubic-bezier(0.4, 0, 0.2, 1);
      --pad: 2rem;
      --ff-serif: 'Instrument Serif', serif;
      --ff-sans: 'Inter', sans-serif;
      --shadow-lg: 0 20px 50px -12px rgba(0, 0, 0, 0.1);
      --glass-bg: rgba(255, 255, 255, 0.8);
      --glass-border: rgba(255, 255, 255, 0.5);
    }
    @keyframes wt-fade-in {
      from { opacity: 0; transform: translateY(15px); }
      to { opacity: 1; transform: translateY(0); }
    }
    .date-calc-container {
      max-width: 1200px;
      margin: 6rem auto 4rem;
      padding: 0 var(--pad);
      animation: wt-fade-in 0.6s var(--ease);
    }
    .calc-hero-header {
      text-align: center;
      margin-bottom: 4rem;
    }
    .calc-hero-header h1 {
      font-family: var(--ff-serif);
      font-size: clamp(40px, 5vw, 64px);
      font-weight: 400;
      line-height: 1.1;
      color: var(--ink);
      margin-bottom: 1.5rem;
    }
    .calc-hero-header h1 em {
      font-style: italic;
      color: var(--calc-primary);
    }
    .calc-hero-header p {
      font-size: 1.1rem;
      color: var(--ink-3);
      max-width: 600px;
      margin: 0 auto;
      line-height: 1.6;
    }
    .dashboard-grid {
      display: grid;
      grid-template-columns: 420px 1fr;
      gap: 2rem;
      align-items: start;
    }
    @media (max-width: 1024px) {
      .dashboard-grid {
        grid-template-columns: 1fr;
      }
    }
    .glass-card {
      background: var(--glass-bg);
      backdrop-filter: blur(12px);
      -webkit-backdrop-filter: blur(12px);
      border: 1px solid var(--glass-border);
      border-radius: 32px;
      box-shadow: var(--shadow-lg);
      padding: 2.5rem;
      transform: translateZ(0);
    }
    .mode-tabs {
      display: flex;
      background: var(--line);
      padding: 4px;
      border-radius: 12px;
      gap: 4px;
      margin-bottom: 2.5rem;
    }
    .mode-tab {
      flex: 1;
      padding: 12px;
      font-size: 0.85rem;
      font-weight: 700;
      color: var(--ink-3);
      cursor: pointer;
      border-radius: 8px;
      transition: all 0.2s;
      text-align: center;
    }
    .mode-tab.active {
      background: var(--white);
      color: var(--calc-primary);
      box-shadow: 0 2px 4px rgba(0,0,0,0.05);
    }
    .input-group {
      margin-bottom: 2rem;
    }
    .input-header {
      display: flex;
      justify-content: space-between;
      align-items: center;
      margin-bottom: 0.75rem;
    }
    .input-header label {
      font-size: 0.9rem;
      font-weight: 700;
      color: var(--ink-2);
      display: flex;
      align-items: center;
      gap: 8px;
    }
    .input-header label svg {
      width: 18px;
      height: 18px;
      color: var(--calc-primary);
    }
    .input-wrapper {
      position: relative;
      display: flex;
      align-items: center;
    }
    .input-wrapper input {
      width: 100%;
      background: var(--white);
      border: 1.5px solid var(--line);
      border-radius: 14px;
      padding: 12px 16px;
      font-family: var(--ff-sans);
      font-size: 1.1rem;
      font-weight: 700;
      color: var(--ink);
      outline: none;
      transition: all 0.2s var(--ease);
    }
    .input-wrapper input:focus {
      border-color: var(--calc-primary);
      box-shadow: 0 0 0 4px var(--calc-primary-light);
    }
    .add-subtract-controls {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 1rem;
      margin-top: 1rem;
    }
    .results-area {
      display: flex;
      flex-direction: column;
      gap: 1.5rem;
    }
    .bento-card {
      background: var(--white);
      border: 1px solid var(--line);
      border-radius: 28px;
      padding: 2.5rem;
      transition: transform 0.3s var(--ease);
    }
    .bento-card:hover {
      transform: translateY(-5px);
      border-color: var(--calc-primary);
    }
    .bento-card.primary {
      background: linear-gradient(135deg, var(--calc-primary) 0%, var(--calc-primary-dark) 100%);
      color: var(--white);
      text-align: center;
    }
    .bento-label {
      font-size: 0.85rem;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.1em;
      margin-bottom: 1.5rem;
      opacity: 0.9;
    }
    .bento-value-main {
      font-size: clamp(3rem, 6vw, 5rem);
      font-weight: 800;
      line-height: 1;
      margin-bottom: 1rem;
    }
    .bento-subtext {
      font-size: 1.1rem;
      opacity: 0.8;
      font-weight: 500;
    }
    .stats-grid {
      display: grid;
      grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
      gap: 1.5rem;
    }
    .stat-box {
      background: var(--off);
      padding: 1.5rem;
      border-radius: 20px;
      border: 1px solid var(--line);
    }
    .stat-label {
      font-size: 0.75rem;
      font-weight: 700;
      color: var(--ink-3);
      text-transform: uppercase;
      margin-bottom: 0.5rem;
    }
    .stat-value {
      font-size: 1.5rem;
      font-weight: 800;
      color: var(--ink);
    }
    .seo-content {
      margin-top: 8rem;
      padding-top: 4rem;
      border-top: 1px solid var(--line);
      display: grid;
      grid-template-columns: 1fr 380px;
      gap: 5rem;
    }
    @media (max-width: 960px) {
      .seo-content {
        grid-template-columns: 1fr;
      }
    }
    .article-text h2 {
      font-family: var(--ff-serif);
      font-size: 2.5rem;
      margin-bottom: 2rem;
      color: var(--ink);
    }
    .article-text h3 {
      font-size: 1.5rem;
      font-weight: 700;
      margin: 3rem 0 1.5rem;
      color: var(--ink);
    }
    .article-text p {
      font-size: 1.15rem;
      line-height: 1.8;
      color: var(--ink-2);
      margin-bottom: 1.5rem;
    }
    .sidebar-guide {
      background: var(--off);
      border: 1px solid var(--line);
      border-radius: 32px;
      padding: 2.5rem;
      height: fit-content;
      position: sticky;
      top: 100px;
    }
    .sidebar-guide h4 {
      font-size: 1.25rem;
      font-weight: 700;
      margin-bottom: 1.5rem;
      color: var(--ink);
    }
    .guide-item {
      margin-bottom: 2rem;
    }
    .guide-item strong {
      display: block;
      font-size: 1rem;
      margin-bottom: 0.5rem;
      color: var(--calc-primary);
    }
    .guide-item p {
      font-size: 0.95rem;
      color: var(--ink-3);
      line-height: 1.6;
    }
    .hidden { display: none !important; }
    .operation-selector {
      display: flex;
      gap: 10px;
      margin-bottom: 2rem;
    }
    .op-btn {
      flex: 1;
      padding: 12px;
      border: 1.5px solid var(--line);
      border-radius: 14px;
      text-align: center;
      font-weight: 700;
      cursor: pointer;
      transition: all 0.2s;
      background: var(--white);
      color: var(--ink-2);
    }
    .op-btn.active {
      border-color: var(--calc-primary);
      background: var(--calc-primary-light);
      color: var(--calc-primary);
    }