:root {
      --primary-color: #6a1b9a;
      --secondary-color: #00acc1;
      --accent-color: #ffab40;
      --light-bg: #f5f5f5;
      --dark-text: #333;
      --light-text: #fff;
      --success-color: #4caf50;
    }

    body {
      margin: 0;
      padding: 0;
      font-family: 'Poppins', sans-serif;
      background: linear-gradient(135deg, #f5f7fa, #e1f5fe);
      color: var(--dark-text);
      min-height: 100vh;
    }

    .container {
      max-width: 1200px;
      margin: 0 auto;
      padding: 20px;
    }

    header {
      /* background: linear-gradient(135deg, var(--primary-color), #9c27b0);
      color: var(--light-text); */
      padding: 20px 0;
      box-shadow: 0 4px 12px rgba(0,0,0,0.1);
      margin-bottom: 30px;
      margin-top: 30px;
    }

    .header-content {
      display: flex;
      justify-content: space-between;
      align-items: center;
      flex-wrap: wrap;
    }

    h1 {
      margin: 0;
      font-size: 2.2rem;
      font-weight: 600;
      text-shadow: 1px 1px 3px rgba(0,0,0,0.2);
    }

    .search-container {
      display: flex;
      max-width: 500px;
      width: 100%;
      margin: 20px 0;
    }

    .search-input {
      flex-grow: 1;
      padding: 12px 20px;
      border: none;
      border-radius: 30px 0 0 30px;
      font-size: 16px;
      outline: none;
      box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    }

    .search-button {
      padding: 12px 20px;
      background-color: var(--accent-color);
      color: var(--light-text);
      border: none;
      border-radius: 0 30px 30px 0;
      cursor: pointer;
      font-weight: 600;
      transition: all 0.3s ease;
      box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    }

    .search-button:hover {
      background-color: #ff9100;
    }

    .filter-container {
      display: flex;
      justify-content: center;
      flex-wrap: wrap;
      gap: 10px;
      margin-bottom: 30px;
    }

    .filter-btn {
      padding: 8px 16px;
      background-color: var(--light-text);
      border: 1px solid #ddd;
      border-radius: 20px;
      cursor: pointer;
      transition: all 0.3s ease;
      font-size: 14px;
    }

    .filter-btn:hover, .filter-btn.active {
      background-color: var(--primary-color);
      color: var(--light-text);
      border-color: var(--primary-color);
    }

    .papers-grid {
      display: grid;
      grid-template-columns: repeat(auto-fill, minmax(350px, 1fr));
      gap: 25px;
      padding: 10px;
    }

    .paper-card {
      background: var(--light-text);
      border-radius: 15px;
      box-shadow: 0 6px 15px rgba(0,0,0,0.08);
      padding: 25px;
      transition: all 0.3s ease;
      position: relative;
      overflow: hidden;
    }

    .paper-card:hover {
      transform: translateY(-5px);
      box-shadow: 0 12px 20px rgba(0,0,0,0.15);
    }

    .paper-card::before {
      content: '';
      position: absolute;
      top: 0;
      left: 0;
      width: 5px;
      height: 100%;
      background-color: var(--primary-color);
    }

    .paper-card h3 {
      margin: 0 0 10px;
      font-size: 1.3rem;
      color: var(--primary-color);
      font-weight: 600;
    }

    .paper-meta {
      display: flex;
      justify-content: space-between;
      margin-bottom: 15px;
      font-size: 0.9rem;
      color: #666;
    }

    .paper-subject {
      font-weight: 500;
      color: var(--secondary-color);
      margin-bottom: 10px;
    }

    .paper-actions {
      display: flex;
      gap: 10px;
      margin-top: 15px;
    }

    .action-btn {
      display: inline-flex;
      align-items: center;
      justify-content: center;
      text-decoration: none;
      font-weight: 500;
      font-size: 14px;
      padding: 10px 18px;
      border-radius: 8px;
      border: none;
      cursor: pointer;
      transition: all 0.3s ease;
      gap: 8px;
    }

    .view-btn {
      background-color: var(--primary-color);
      color: var(--light-text);
    }

    .view-btn:hover {
      background-color: #7b1fa2;
    }

    .subscribe-btn {
      background-color: var(--secondary-color);
      color: var(--light-text);
    }

    .subscribe-btn:hover {
      background-color: #00838f;
    }

    .popularity {
      display: flex;
      align-items: center;
      color: #666;
      font-size: 0.85rem;
      margin-top: 10px;
    }

    .popularity i {
      color: var(--accent-color);
      margin-right: 5px;
    }

    .free-badge {
      position: absolute;
      top: 15px;
      right: 15px;
      background-color: var(--success-color);
      color: white;
      padding: 3px 10px;
      border-radius: 12px;
      font-size: 0.75rem;
      font-weight: 600;
    }

    .semester-tag {
      background-color: #e1bee7;
      color: var(--primary-color);
      padding: 3px 10px;
      border-radius: 12px;
      font-size: 0.75rem;
      font-weight: 600;
      display: inline-block;
      margin-right: 8px;
    }

    .no-results {
      text-align: center;
      grid-column: 1 / -1;
      padding: 50px;
      color: #666;
    }

    @keyframes fadeIn {
      from { opacity: 0; transform: translateY(20px); }
      to { opacity: 1; transform: translateY(0); }
    }

    .paper-card {
      animation: fadeIn 0.5s ease-out forwards;
      opacity: 0;
    }

    @media (max-width: 768px) {
      .header-content {
        flex-direction: column;
        text-align: center;
      }
      
      .search-container {
        margin-top: 15px;
      }
      
      .papers-grid {
        grid-template-columns: 1fr;
      }
      
      h1 {
        font-size: 1.8rem;
      }
    }

    /* Unique feature: Dark mode toggle */
    .dark-mode {
      background: linear-gradient(135deg, #121212, #1e1e1e);
      color: #f0f0f0;
    }
    
    .dark-mode .paper-card {
      background: #2d2d2d;
      color: #f0f0f0;
    }
    
    .dark-mode .paper-meta,
    .dark-mode .paper-subject {
      color: #b0b0b0;
    }
    
    .theme-toggle {
      position: fixed;
      bottom: 20px;
      right: 20px;
      width: 50px;
      height: 50px;
      border-radius: 50%;
      background-color: var(--primary-color);
      color: white;
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      box-shadow: 0 4px 10px rgba(0,0,0,0.2);
      z-index: 100;
      border: none;
      font-size: 1.2rem;
    }