:root {
        --primary: #4a6fa5;
        --primary-light: #6d8dc1;
        --secondary: #5a9b7d;
        --secondary-light: #7bbf9e;
        --accent: #e67e22;
        --light-bg: #f8f9fa;
        --light-card: #ffffff;
        --text-primary: #2c3e50;
        --text-secondary: #546e7a;
        --border: #e0e6ed;
        --shadow: rgba(0, 0, 0, 0.05);
        --shadow-hover: rgba(0, 0, 0, 0.08);
        --success: #27ae60;
        --warning: #f39c12;
        --danger: #e74c3c;
        --radius: 12px;
        --radius-sm: 8px;
        --transition: all 0.3s ease;
      }

      * {
        margin: 0;
        padding: 0;
        box-sizing: border-box;
      }

      body {
        font-family: "Roboto", sans-serif;
        color: var(--text-primary);
        background-color: var(--light-bg);
        line-height: 1.6;
        overflow-x: hidden;
      }

      h1,
      h2,
      h3,
      h4,
      h5 {
        font-family: "Poppins", sans-serif;
        font-weight: 600;
      }

      .container {
        width: 100%;
        max-width: 1200px;
        margin: 0 auto;
        padding: 0 20px;
      }

      /* Header & Navigation */
      header {
        background-color: var(--light-card);
        box-shadow: 0 2px 15px var(--shadow);
        position: sticky;
        top: 0;
        z-index: 1000;
      }

      nav {
        display: flex;
        justify-content: space-between;
        align-items: center;
        padding: 15px 0;
      }

      .logo {
        display: flex;
        align-items: center;
        gap: 10px;
        font-size: 1.5rem;
        font-weight: 700;
        color: var(--primary);
        text-decoration: none;
      }

      .logo i {
        color: var(--secondary);
      }

      .nav-links {
        display: flex;
        list-style: none;
        gap: 25px;
        margin: 0;
        padding: 0;
      }

      .nav-links a {
        text-decoration: none;
        color: var(--text-primary);
        font-weight: 500;
        transition: var(--transition);
        padding: 5px 0;
        position: relative;
      }

      .nav-links a:hover {
        color: var(--primary);
      }

      .nav-links a.active {
        color: var(--primary);
      }

      .nav-links a.active::after {
        content: "";
        position: absolute;
        bottom: 0;
        left: 0;
        width: 100%;
        height: 2px;
        background-color: var(--primary);
      }

      .mobile-menu-btn {
        display: none;
        font-size: 1.5rem;
        background: none;
        border: none;
        color: var(--primary);
        cursor: pointer;
      }

      /* Hero Section */
      .hero {
        padding: 80px 0;
        background: linear-gradient(
          135deg,
          rgba(74, 111, 165, 0.05) 0%,
          rgba(90, 155, 125, 0.05) 100%
        );
        text-align: center;
        border-bottom: 1px solid var(--border);
      }

      .hero h1 {
        font-size: 2.8rem;
        margin-bottom: 15px;
        color: var(--text-primary);
      }

      .hero p {
        font-size: 1.2rem;
        max-width: 800px;
        margin: 0 auto 30px;
        color: var(--text-secondary);
      }

      .cta-button {
        display: inline-block;
        background-color: var(--primary);
        color: white;
        padding: 12px 28px;
        border-radius: var(--radius);
        text-decoration: none;
        font-weight: 500;
        transition: var(--transition);
        box-shadow: 0 4px 12px rgba(74, 111, 165, 0.2);
      }

      .cta-button:hover {
        background-color: var(--primary-light);
        transform: translateY(-3px);
        box-shadow: 0 6px 16px rgba(74, 111, 165, 0.25);
      }

      /* CTA Button Animation */
      .cta-button.bounce {
        animation: bounceAnimation 0.5s ease;
      }

      @keyframes bounceAnimation {
        0%,
        100% {
          transform: translateY(0);
        }
        50% {
          transform: translateY(-10px);
        }
      }

      /* Section Styling */
      section {
        padding: 70px 0;
      }

      .section-title {
        text-align: center;
        margin-bottom: 50px;
      }

      .section-title h2 {
        font-size: 2.2rem;
        color: var(--primary);
        margin-bottom: 15px;
      }

      .section-title p {
        max-width: 700px;
        margin: 0 auto;
        color: var(--text-secondary);
      }

      /* Use Case Diagram */
      .diagram-container {
        background-color: var(--light-card);
        border-radius: var(--radius);
        padding: 30px;
        box-shadow: 0 5px 20px var(--shadow);
        margin-bottom: 40px;
        position: relative;
        overflow: hidden;
      }

      .diagram-container::before {
        content: "";
        position: absolute;
        top: 0;
        left: 0;
        width: 100%;
        height: 5px;
        background: linear-gradient(to right, var(--primary), var(--secondary));
      }

      .diagram-title {
        display: flex;
        align-items: center;
        gap: 10px;
        margin-bottom: 25px;
      }

      .diagram-title i {
        color: var(--secondary);
        font-size: 1.5rem;
      }

      .use-case-diagram {
        display: flex;
        flex-direction: column;
        align-items: center;
        position: relative;
        min-height: 500px;
      }

      .actors {
        display: flex;
        justify-content: space-around;
        width: 100%;
        margin-bottom: 50px;
      }

      .actor {
        display: flex;
        flex-direction: column;
        align-items: center;
        cursor: pointer;
        transition: var(--transition);
        padding: 15px;
        border-radius: var(--radius-sm);
      }

      .actor:hover {
        background-color: rgba(74, 111, 165, 0.05);
        transform: translateY(-5px);
      }

      .actor-icon {
        width: 80px;
        height: 80px;
        border-radius: 50%;
        display: flex;
        align-items: center;
        justify-content: center;
        margin-bottom: 10px;
        font-size: 1.8rem;
        color: white;
        box-shadow: 0 4px 8px var(--shadow);
      }

      .actor.student .actor-icon {
        background-color: var(--primary);
      }

      .actor.librarian .actor-icon {
        background-color: var(--secondary);
      }

      .actor.system .actor-icon {
        background-color: var(--accent);
      }

      .use-cases {
        display: grid;
        grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
        gap: 20px;
        width: 100%;
        margin-bottom: 30px;
      }

      .use-case {
        background-color: var(--light-bg);
        border-radius: var(--radius-sm);
        padding: 20px;
        text-align: center;
        cursor: pointer;
        transition: var(--transition);
        border: 1px solid var(--border);
        position: relative;
      }

      .use-case:hover {
        background-color: white;
        transform: translateY(-5px);
        box-shadow: 0 5px 15px var(--shadow-hover);
      }

      .use-case.active {
        border-color: var(--primary);
        background-color: rgba(74, 111, 165, 0.05);
      }

      .use-case-icon {
        width: 50px;
        height: 50px;
        border-radius: 50%;
        display: flex;
        align-items: center;
        justify-content: center;
        margin: 0 auto 15px;
        font-size: 1.3rem;
        color: white;
      }

      .login .use-case-icon {
        background-color: var(--primary);
      }

      .search .use-case-icon {
        background-color: var(--secondary);
      }

      .borrow .use-case-icon {
        background-color: #9b59b6;
      }

      .return .use-case-icon {
        background-color: var(--accent);
      }

      .manage .use-case-icon {
        background-color: var(--danger);
      }

      .connections {
        position: absolute;
        width: 100%;
        height: 100px;
        top: 50%;
        left: 0;
        pointer-events: none;
        z-index: -1;
      }

      .connection {
        position: absolute;
        height: 2px;
        background-color: var(--border);
        transform-origin: left center;
      }

      /* Use Case Details */
      .use-case-details {
        background-color: var(--light-card);
        border-radius: var(--radius);
        padding: 0;
        box-shadow: 0 5px 20px var(--shadow);
        margin-bottom: 30px;
        overflow: hidden;
        display: block;
      }

      .use-case-header {
        padding: 25px 30px;
        background-color: rgba(74, 111, 165, 0.05);
        border-bottom: 1px solid var(--border);
        cursor: pointer;
        display: flex;
        justify-content: space-between;
        align-items: center;
      }

      .use-case-header h3 {
        display: flex;
        align-items: center;
        gap: 10px;
        color: var(--primary);
      }

      .use-case-header i {
        transition: var(--transition);
      }

      .use-case-content {
        padding: 0;
        max-height: 0;
        overflow: hidden;
        transition: var(--transition);
      }

      .use-case-details.active .use-case-content {
        padding: 30px;
        max-height: 2000px;
      }

      .use-case-details.active .use-case-header i {
        transform: rotate(360deg);
      }

      .details-grid {
        display: grid;
        grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
        gap: 25px;
      }

      .detail-card {
        background-color: var(--light-bg);
        border-radius: var(--radius-sm);
        padding: 20px;
        border-left: 4px solid var(--primary);
      }

      .detail-card h4 {
        margin-bottom: 10px;
        color: var(--primary);
        display: flex;
        align-items: center;
        gap: 8px;
      }

      .flow-list {
        list-style-type: none;
      }

      .flow-list li {
        padding: 8px 0;
        border-bottom: 1px dashed var(--border);
        position: relative;
        padding-left: 25px;
      }

      .flow-list li:before {
        content: "✓";
        position: absolute;
        left: 0;
        color: var(--success);
        font-weight: bold;
      }

      .error-flow li:before {
        content: "⚠";
        color: var(--warning);
      }

      /* Librarian Capabilities */
      .capabilities-grid {
        display: grid;
        grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
        gap: 25px;
      }

      .capability-card {
        background-color: var(--light-card);
        border-radius: var(--radius);
        padding: 30px 25px;
        text-align: center;
        box-shadow: 0 5px 15px var(--shadow);
        transition: var(--transition);
        border-top: 4px solid var(--secondary);
      }

      .capability-card:hover {
        transform: translateY(-10px);
        box-shadow: 0 10px 25px var(--shadow-hover);
      }

      .capability-icon {
        width: 70px;
        height: 70px;
        border-radius: 50%;
        display: flex;
        align-items: center;
        justify-content: center;
        margin: 0 auto 20px;
        font-size: 1.8rem;
        color: white;
        background-color: var(--secondary);
      }

      /* Security Section */
      .security-container {
        background-color: var(--light-card);
        border-radius: var(--radius);
        padding: 40px;
        box-shadow: 0 5px 20px var(--shadow);
        display: grid;
        grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
        gap: 30px;
      }

      .security-feature {
        display: flex;
        gap: 20px;
        align-items: flex-start;
      }

      .security-icon {
        width: 60px;
        height: 60px;
        border-radius: 50%;
        display: flex;
        align-items: center;
        justify-content: center;
        font-size: 1.5rem;
        color: white;
        background-color: var(--primary);
        flex-shrink: 0;
      }

      /* Demo Section */
      .demo-container {
        background-color: var(--light-card);
        border-radius: var(--radius);
        padding: 40px;
        box-shadow: 0 5px 20px var(--shadow);
        max-width: 800px;
        margin: 0 auto;
      }

      .demo-tabs {
        display: flex;
        margin-bottom: 30px;
        border-bottom: 1px solid var(--border);
      }

      .demo-tab {
        padding: 12px 25px;
        background: none;
        border: none;
        font-size: 1rem;
        font-weight: 500;
        color: var(--text-secondary);
        cursor: pointer;
        transition: var(--transition);
        position: relative;
      }

      .demo-tab.active {
        color: var(--primary);
      }

      .demo-tab.active::after {
        content: "";
        position: absolute;
        bottom: -1px;
        left: 0;
        width: 100%;
        height: 3px;
        background-color: var(--primary);
      }

      .demo-content {
        min-height: 300px;
      }

      .demo-tab-content {
        display: none;
      }

      .demo-tab-content.active {
        display: block;
        animation: fadeIn 0.5s ease;
      }

      .login-form {
        max-width: 400px;
        margin: 0 auto;
      }

      .form-group {
        margin-bottom: 20px;
      }

      .form-group label {
        display: block;
        margin-bottom: 8px;
        font-weight: 500;
      }

      .form-group input,
      .form-group select {
        width: 100%;
        padding: 12px 15px;
        border: 1px solid var(--border);
        border-radius: var(--radius-sm);
        font-size: 1rem;
        transition: var(--transition);
      }

      .form-group input:focus,
      .form-group select:focus {
        outline: none;
        border-color: var(--primary);
        box-shadow: 0 0 0 3px rgba(74, 111, 165, 0.1);
      }

      .demo-button {
        background-color: var(--primary);
        color: white;
        border: none;
        padding: 12px 25px;
        border-radius: var(--radius-sm);
        font-size: 1rem;
        font-weight: 500;
        cursor: pointer;
        transition: var(--transition);
        width: 100%;
        margin-top: 10px;
      }

      .demo-button:hover {
        background-color: var(--primary-light);
      }

      .demo-result {
        margin-top: 25px;
        padding: 20px;
        border-radius: var(--radius-sm);
        background-color: rgba(39, 174, 96, 0.1);
        border: 1px solid rgba(39, 174, 96, 0.3);
        display: none;
      }

      .demo-result.active {
        display: block;
        animation: fadeIn 0.5s ease;
      }

      /* Footer */
      footer {
        background-color: var(--text-primary);
        color: white;
        padding: 60px 0 30px;
      }

      .footer-content {
        display: grid;
        grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
        gap: 40px;
        margin-bottom: 40px;
      }

      .footer-section h3 {
        margin-bottom: 20px;
        font-size: 1.3rem;
      }

      .footer-section p {
        color: rgba(255, 255, 255, 0.7);
        margin-bottom: 20px;
      }

      .footer-links {
        list-style: none;
      }

      .footer-links li {
        margin-bottom: 10px;
      }

      .footer-links a {
        color: rgba(255, 255, 255, 0.7);
        text-decoration: none;
        transition: var(--transition);
      }

      .footer-links a:hover {
        color: white;
        padding-left: 5px;
      }

      .copyright {
        text-align: center;
        padding-top: 30px;
        border-top: 1px solid rgba(255, 255, 255, 0.1);
        color: rgba(255, 255, 255, 0.6);
        font-size: 0.9rem;
      }

      /* Animations */
      @keyframes fadeIn {
        from {
          opacity: 0;
          transform: translateY(10px);
        }
        to {
          opacity: 1;
          transform: translateY(0);
        }
      }

      .animate-on-scroll {
        opacity: 0;
        transform: translateY(30px);
        transition: opacity 0.6s ease, transform 0.6s ease;
      }

      .animate-on-scroll.visible {
        opacity: 1;
        transform: translateY(0);
      }

      /* Responsive Design */
      @media (max-width: 992px) {
        .hero h1 {
          font-size: 2.3rem;
        }

        .use-case-diagram {
          min-height: 450px;
        }
      }

      @media (max-width: 768px) {
        .mobile-menu-btn {
          display: block;
        }

        .nav-links {
          position: fixed;
          top: 70px;
          left: 0;
          width: 100%;
          background-color: var(--light-card);
          flex-direction: column;
          padding: 20px;
          box-shadow: 0 5px 10px var(--shadow);
          transform: translateY(-100%);
          opacity: 0;
          visibility: hidden;
          transition: var(--transition);
          z-index: 999;
          gap: 15px;
        }

        .nav-links.active {
          transform: translateY(0);
          opacity: 1;
          visibility: visible;
        }

        .hero {
          padding: 60px 0;
        }

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

        section {
          padding: 50px 0;
        }

        .section-title h2 {
          font-size: 1.8rem;
        }

        .use-case-diagram {
          min-height: 400px;
        }

        .actors {
          flex-direction: column;
          align-items: center;
          gap: 30px;
          margin-bottom: 30px;
        }

        .security-container,
        .demo-container {
          padding: 25px;
        }
      }

      @media (max-width: 480px) {
        .hero h1 {
          font-size: 1.8rem;
        }

        .section-title h2 {
          font-size: 1.6rem;
        }

        .diagram-container,
        .use-case-details {
          padding: 20px;
        }

        .use-case-header {
          padding: 20px;
        }

        .use-case-details.active .use-case-content {
          padding: 20px;
        }
      }