:root {
      --primary: #0077cc; /* Walrus blue/grey */
      --secondary: #4A3B31; /* Dark brown, like tusks or rocks */
      --light: #f0f8ff; /* Icy light blue */
      --dark: #2c3e50; /* Dark ocean blue */
      --accent: #d4a373; /* Sandy beige, like tusks */
      --transition: all 0.3s ease;
    }
    
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
      font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    }
    
    body {
      background-color: var(--light);
      color: var(--dark);
      line-height: 1.7; 
    }
    
    header {
      background-color: var(--secondary);
      color: white;
      padding: 1rem;
      position: sticky;
      top: 0;
      z-index: 100;
      box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    }
    
    nav {
      display: flex;
      justify-content: space-between;
      align-items: center;
      max-width: 1200px;
      margin: 0 auto;
    }
    
    .logo {
      font-size: 1.5rem;
      font-weight: bold;
      display: flex;
      align-items: center;
    }
    
    .logo span {
      color: var(--primary);
    }
    
    .nav-links {
      display: flex;
      gap: 2rem;
    }
    
    .nav-links a {
      color: white;
      text-decoration: none;
      font-weight: 500;
      transition: var(--transition);
    }
    
    .nav-links a:hover {
      color: var(--primary);
    }
        
    main {
      max-width: 1200px;
      margin: 0 auto;
      padding: 2rem 1rem;
    }
    
    .hero {
      position: relative;
      height: 450px; 
      /* background is set inline in HTML */
      border-radius: 12px;
      overflow: hidden;
      display: flex;
      align-items: flex-end;
      margin-bottom: 3rem;
    }
    
    .hero-content {
      padding: 2rem;
      color: white;
      width: 100%;
      background: linear-gradient(transparent, rgba(0,0,0,0.8));
    }
    
    .hero h1 {
      font-size: 2.8rem; 
      margin-bottom: 1rem;
      text-shadow: 1px 1px 3px rgba(0,0,0,0.5);
    }
    
    .article-meta {
      display: flex;
      align-items: center;
      gap: 1rem;
      margin-bottom: 1rem; 
      font-size: 0.9rem;
    }
    
    .author {
      display: flex;
      align-items: center;
      gap: 0.5rem;
    }
    
    .author-img {
      width: 40px;
      height: 40px;
      border-radius: 50%;
      /* background is set inline in HTML */
      border: 2px solid var(--light);
    }
    
    .share-buttons {
      display: flex;
      gap: 0.5rem;
    }
    
    .share-btn, .share-btn-1 { 
      width: 36px;
      height: 36px;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      transition: var(--transition);
      font-weight: bold;
      color: var(--secondary); 
    }
    .share-btn-1 { 
      background-color: #1877F2; 
      color: white;
    }   
    .share-btn { 
      background-color: #1DA1F2; 
      color: white;
    }
    
    .share-btn:hover, .share-btn-1:hover {
      opacity: 0.8;
      transform: scale(1.1);
    }
    
    .table-of-contents {
      background-color: white;
      border-radius: 12px;
      padding: 1.5rem;
      margin-bottom: 3rem;
      box-shadow: 0 5px 15px rgba(0,0,0,0.05);
    }
    
    .toc-title {
      font-size: 1.3rem; 
      margin-bottom: 1rem;
      color: var(--secondary);
      font-weight: 600;
    }
    
    .toc-links {
      display: grid; 
      grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); 
      gap: 1rem;
    }
    
    .toc-link {
      background-color: var(--light);
      padding: 0.8rem 1.2rem;
      border-radius: 8px;
      text-decoration: none;
      color: var(--dark);
      font-weight: 500;
      transition: var(--transition);
      box-shadow: 0 2px 5px rgba(0,0,0,0.05);
      text-align: center;
    }
    
    .toc-link:hover {
      background-color: var(--primary);
      color: white;
      transform: translateY(-3px);
    }
    
    article {
      display: grid;
      grid-template-columns: 1fr;
      gap: 2.5rem; 
    }
    
    @media (min-width: 992px) {
      article {
        grid-template-columns: 3fr 1fr;
      }
    }
    
    .article-content {
      background-color: white;
      border-radius: 12px;
      padding: 2.5rem; 
      box-shadow: 0 5px 15px rgba(0,0,0,0.05);
    }
    
    .section {
      margin-bottom: 3rem;
    }
    
    .section-title {
      font-size: 2rem; 
      color: var(--secondary);
      margin-bottom: 1.5rem;
      position: relative;
      padding-bottom: 0.75rem; 
    }
    
    .section-title::after {
      content: '';
      position: absolute;
      bottom: 0;
      left: 0;
      width: 70px; 
      height: 4px; 
      background-color: var(--primary);
      border-radius: 2px;
    }

    .article-content p {
        margin-bottom: 1.2rem; 
    }

    .article-content h3 {
        font-size: 1.5rem;
        color: var(--accent);
        margin-top: 2rem;
        margin-bottom: 1rem;
    }
    
    .article-content ul {
        list-style-type: disc;
        margin-left: 20px;
        padding-left: 10px;
        margin-bottom: 1.2rem;
    }
    .article-content li {
        margin-bottom: 0.5rem;
    }

    .fact-card {
      background-color: #eaf5ff; 
      border-left: 5px solid var(--primary);
      border-radius: 0 8px 8px 0; 
      padding: 1.5rem;
      margin-bottom: 1.5rem; 
      transition: var(--transition);
    }
    
    .fact-card:hover {
      transform: translateX(5px);
      box-shadow: 0 8px 20px rgba(0,0,0,0.08);
    }

    .fact-card ul {
        list-style-type: disc; 
        margin-left: 20px;
        padding-left: 10px;
    }
    .fact-card li {
        margin-bottom: 0.5rem;
    }
        
    .img-container {
      margin: 2rem 0;
      border-radius: 12px;
      overflow: hidden;
      box-shadow: 0 4px 12px rgba(0,0,0,0.1);
    }
    
    .img-container img {
      width: 100%;
      height: auto;
      display: block; 
      transition: var(--transition);
    }
    
    .img-container:hover img {
      transform: scale(1.03);
    }
    
    .sidebar {
      position: sticky;
      top: calc(60px + 2rem); 
      align-self: start; 
    }

    .sidebar-section {
      background-color: white;
      border-radius: 12px;
      padding: 1.5rem;
      margin-bottom: 2rem;
      box-shadow: 0 5px 15px rgba(0,0,0,0.05);
    }

    .sidebar-title {
      font-size: 1.2rem;
      margin-bottom: 1rem;
      color: var(--secondary);
      font-weight: 600;
    }

    .ad-container {
      text-align: center; 
    }

    .ad-unit {
      margin: 0 auto; 
    }

    .conclusion {
      background-color: var(--secondary);
      color: white;
      padding: 2.5rem; 
      border-radius: 12px;
      margin-top: 3rem;
    }

    .conclusion-title {
      font-size: 1.8rem;
      margin-bottom: 1rem;
      color: var(--primary);
    }

    footer {
      background-color: var(--secondary);
      color: white;
      padding: 2.5rem 1rem; 
      margin-top: 3rem;
    }

    .footer-content {
      max-width: 1200px;
      margin: 0 auto;
      text-align: center;
    }
    .footer-content a {
        color: #ADD8E6; 
        text-decoration: none;
    }
    .footer-content a:hover {
        text-decoration: underline;
    }

    .scroll-top {
      position: fixed;
      bottom: 30px;
      right: 30px;
      width: 50px;
      height: 50px;
      background-color: var(--primary);
      color: white;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 1.5rem;
      cursor: pointer;
      box-shadow: 0 3px 10px rgba(0,0,0,0.2);
      transition: var(--transition);
      z-index: 999;
    }

    .scroll-top:hover {
      transform: translateY(-5px);
      background-color: var(--accent); 
    }

    @media (max-width: 768px) {
      .hero {
        height: 350px;
      }

      .hero h1 {
        font-size: 2rem; 
      }

      .section-title {
        font-size: 1.6rem; 
      }
      .article-content {
        padding: 1.5rem;
      }
      .sidebar {
        position: static; 
        margin-top: 2rem;
      }
    }

    @media (max-width: 576px) {
      .nav-links {
        display: none; 
      }

      .hero {
        height: 300px; 
        margin-bottom: 2rem;
      }

      .hero-content {
        padding: 1.5rem;
      }
      .hero h1 {
        font-size: 1.8rem;
      }

      .article-meta {
        flex-direction: column;
        align-items: flex-start;
        gap: 0.8rem; 
      }
      .table-of-contents {
        padding: 1rem;
      }
      .toc-links {
        grid-template-columns: 1fr; 
      }
    }

    .progress-container {
      position: fixed;
      top: 0; 
      left: 0;
      width: 100%;
      height: 5px;
      z-index: 200;
    }

    .progress-bar {
      height: 5px;
      background-color: var(--primary);
      width: 0;
      transition: width 0.1s linear; 
    }

    @keyframes fadeIn {
      from { opacity: 0; transform: translateY(15px); }
      to { opacity: 1; transform: translateY(0); }
    }

    .section {
      animation: fadeIn 0.6s ease-out forwards; 
    }

    a:focus, button:focus, .toc-link:focus, .scroll-top:focus {
        outline: 2px solid var(--accent);
        outline-offset: 2px;
    }