:root {
      --white: #ffffff;
      --box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
      --title: #3f37c9;
      --primary-color: #4361ee;
      --primary-light: #e0e7ff;
      --secondary-color: #3f37c9;
      --accent-color: #4cc9f0;
      --dark-color: #1a1a2e;
      --light-color: #f8f9fa;
      --error-color: #f72585;
      --text-color: #333;
      --text-light: #6b7280;
      --shadow-sm: 0 1px 3px rgba(0,0,0,0.12);
      --shadow-md: 0 4px 6px rgba(0,0,0,0.1);
      --shadow-lg: 0 10px 25px rgba(0,0,0,0.1);
      --transition: all 0.3s ease;
      --border-radius: 12px;
      --border-radius-sm: 8px;
    }
    
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }
    
    body {
      font-family: 'Inter', sans-serif;
      background-color: #f5f7ff;
      color: var(--text-color);
      line-height: 1.6;
    }
    
    .container {
      max-width: 1200px;
      margin: 0 auto;
      padding: 0 20px;
    }
    
    /* Header Styles */
    header {
      background-color: var(--white);
      box-shadow: var(--box-shadow);
      position: sticky;
      top: 0;
      z-index: 100;
    }
    
    .navbar {
      display: flex;
      justify-content: space-between;
      align-items: center;
      padding: 20px 0;
      position: relative;
    }
    
    .logo {
      display: flex;
      align-items: center;
      gap: 10px;
      text-decoration: none;
      z-index: 101;
    }
    
    .logo img {
      height: 40px;
      width: auto;
    }
    
    .logo-text {
      font-size: 1.5rem;
      font-weight: 700;
      color: var(--primary-color);
    }
    
    .nav-links {
      display: flex;
      gap: 25px;
      transition: var(--transition);
    }
    
    .nav-link {
      text-decoration: none;
      color: var(--dark-color);
      font-weight: 500;
      transition: var(--transition);
      display: flex;
      align-items: center;
      gap: 5px;
    }
    
    .nav-link:hover {
      color: var(--primary-color);
    }
    
    .mobile-menu-btn {
      display: none;
      background: none;
      border: none;
      font-size: 1.5rem;
      color: var(--dark-color);
      cursor: pointer;
      z-index: 101;
    }
    
    /* Mobile Menu Styles */
    @media (max-width: 768px) {
      .nav-links {
        position: fixed;
        top: 80px;
        left: 0;
        width: 100%;
        background-color: var(--white);
        flex-direction: column;
        align-items: center;
        padding: 20px 0;
        box-shadow: var(--shadow-lg);
        z-index: 99;
        transform: translateY(-150%);
        opacity: 0;
        display: flex !important;
      }
      
      .nav-links.active {
        transform: translateY(0);
        opacity: 1;
      }
      
      .nav-link {
        padding: 12px 20px;
        width: 100%;
        text-align: center;
        border-bottom: 1px solid rgba(0,0,0,0.05);
      }
      
      .mobile-menu-btn {
        display: block;
      }
    }

    /* Hero Section */
    .hero {
      text-align: center;
      padding: 60px 0 40px;
    }
    
    .hero h1 {
      font-size: 2.5rem;
      margin-bottom: 15px;
      color: var(--dark-color);
      background: linear-gradient(90deg, var(--primary-color), var(--accent-color));
      -webkit-background-clip: text;
      -webkit-text-fill-color: transparent;
    }
    
    .hero p {
      font-size: 1.1rem;
      color: var(--text-light);
      max-width: 700px;
      margin: 0 auto 30px;
    }
    
    /* Calculator Section */
    .calculator-container {
      display: flex;
      gap: 30px;
      margin-bottom: 60px;
      flex-wrap: wrap;
    }
    
    .calculator-card {
      flex: 1;
      min-width: 300px;
      background: white;
      border-radius: var(--border-radius);
      box-shadow: var(--shadow-lg);
      padding: 30px;
      transition: var(--transition);
    }
    
    .calculator-card:hover {
      transform: translateY(-5px);
    }
    
    .calculator-header {
      margin-bottom: 25px;
    }
    
    .calculator-header h2 {
      font-size: 1.5rem;
      color: var(--dark-color);
      margin-bottom: 10px;
      display: flex;
      align-items: center;
      gap: 10px;
    }
    
    .calculator-header p {
      color: var(--text-light);
      font-size: 0.95rem;
    }
    
    .date-selector {
      margin-bottom: 20px;
    }
    
    .date-selector label {
      display: block;
      margin-bottom: 8px;
      font-weight: 500;
      color: var(--dark-color);
    }
    
    .date-fields {
      display: flex;
      gap: 10px;
      margin-bottom: 20px;
    }
    
    select {
      flex: 1;
      padding: 12px 15px;
      border: 1px solid #e5e7eb;
      border-radius: var(--border-radius-sm);
      font-size: 1rem;
      background-color: white;
      transition: var(--transition);
    }
    
    select:focus {
      outline: none;
      border-color: var(--primary-color);
      box-shadow: 0 0 0 3px var(--primary-light);
    }
    
    .btn {
      display: inline-block;
      padding: 12px 24px;
      background-color: var(--primary-color);
      color: white;
      border: none;
      border-radius: var(--border-radius-sm);
      font-size: 1rem;
      font-weight: 500;
      cursor: pointer;
      transition: var(--transition);
      width: 100%;
      text-align: center;
    }
    
    .btn:hover {
      background-color: var(--secondary-color);
      transform: translateY(-2px);
    }
    
    .results {
      margin-top: 30px;
    }
    
    .result-item {
      background-color: var(--light-color);
      border-radius: var(--border-radius-sm);
      padding: 15px;
      margin-bottom: 15px;
    }
    
    .result-item h3 {
      font-size: 0.9rem;
      color: var(--text-light);
      margin-bottom: 5px;
      display: flex;
      align-items: center;
      gap: 8px;
    }
    
    .result-item p {
      font-size: 1.1rem;
      color: var(--dark-color);
    }
    
    .next-birthday {
      background: linear-gradient(135deg, #f8d5ff, var(--primary-light));
      border-left: 4px solid var(--error-color);
      color: var(--dark-color);
    }
    
    .next-birthday h3 {
      color: var(--error-color);
      font-weight: 600;
    }
    
    /* Info Section */
    .info-section {
      padding: 50px 0;
    }
    
    .info-container {
      max-width: 800px;
      margin: 0 auto;
    }
    
    .info-section h2 {
      text-align: center;
      font-size: 2rem;
      color: var(--primary-color);
      margin-bottom: 40px;
    }
    
    .info-card {
      background-color: var(--white);
      border-radius: var(--border-radius);
      box-shadow: var(--box-shadow);
      padding: 30px;
      margin-bottom: 30px;
    }
    
    .info-card h3 {
      color: var(--title);
      margin-bottom: 15px;
      font-size: 1.4rem;
    }
    
    .info-card p {
      margin-bottom: 15px;
    }
    
    .info-card ul {
      padding-left: 20px;
      margin-bottom: 15px;
    }
    
    .info-card li {
      margin-bottom: 8px;
    }
    
    .info-card strong {
      color: var(--primary-color);
    }
    
    /* Footer */
    footer {
      background-color: var(--dark-color);
      color: white;
      padding: 50px 0 20px;
    }
    
    .footer-content {
      display: grid;
      grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
      gap: 30px;
      margin-bottom: 40px;
    }
    
    .footer-column h3 {
      font-size: 1.2rem;
      margin-bottom: 20px;
      color: white;
    }
    
    .footer-links {
      list-style: none;
    }
    
    .footer-links li {
      margin-bottom: 12px;
    }
    
    .footer-links a {
      color: #d1d5db;
      text-decoration: none;
      transition: var(--transition);
      display: flex;
      align-items: center;
      gap: 8px;
    }
    
    .footer-links a:hover {
      color: white;
    }
    
    .social-links {
      display: flex;
      gap: 15px;
      margin-top: 20px;
    }
    
    .social-links a {
      color: white;
      background-color: var(--dark-color);
      width: 36px;
      height: 36px;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      transition: var(--transition);
      text-decoration: none;
    }
    
    .social-links a:hover {
      background-color: var(--primary-color);
      transform: translateY(-3px);
    }
    
    .copyright {
      text-align: center;
      padding-top: 20px;
      border-top: 1px solid rgba(255,255,255,0.1);
      color: #9ca3af;
      font-size: 0.9rem;
    }
    
    .copyright a {
      color: var(--accent-color);
      text-decoration: none;
      font-weight: 500;
    }
    
    /* Popup styles */
    .popup {
      position: fixed;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      background-color: rgba(0,0,0,0.7);
      display: flex;
      justify-content: center;
      align-items: center;
      z-index: 1000;
      opacity: 0;
      visibility: hidden;
      transition: var(--transition);
    }
    
    .popup.active {
      opacity: 1;
      visibility: visible;
    }
    
    .popup-content {
      background-color: white;
      border-radius: var(--border-radius);
      width: 90%;
      max-width: 800px;
      max-height: 80vh;
      overflow-y: auto;
      padding: 30px;
      position: relative;
      box-shadow: var(--shadow-lg);
    }
    
    .popup-close {
      position: absolute;
      top: 15px;
      right: 15px;
      color: var(--text-light);
      border: none;
      cursor: pointer;
      transition: var(--transition);
      background: var(--primary-light);
      width: 40px;
      height: 40px;
      border-radius: 50%;
      font-size: 1.2rem;
      display: flex;
      align-items: center;
      justify-content: center;
    }
    
    .popup-close:hover {
      background: var(--error-color);
      color: white;
      transform: rotate(90deg);
    }
    
    .popup h2 {
      font-size: 1.8rem;
      margin-bottom: 20px;
      display: flex;
      align-items: center;
      gap: 10px;
    }
    
    .popup p {
      margin-bottom: 15px;
    }
    
    .popup ul {
      padding-left: 20px;
      margin-bottom: 20px;
    }
    
    .popup li {
      margin-bottom: 8px;
    }
    
    /* Animation */
    @keyframes fadeIn {
      from { opacity: 0; transform: translateY(20px); }
      to { opacity: 1; transform: translateY(0); }
    }
    
    .fade-in {
      animation: fadeIn 0.6s ease forwards;
    }
    
    .delay-1 { animation-delay: 0.2s; }
    .delay-2 { animation-delay: 0.4s; }