* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Segoe UI', sans-serif;
    
  }
  
  body {
    background: linear-gradient(to right, #cdfcff, #135eff);
  
  }
  
  .navbar {
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 15px 40px;
    background: url('mountain-bg.jpg') center/cover no-repeat;
    position: relative;
    width: 80%;
  }
  
  .logo img {
    height: 80px;
  padding-left:  60px;
  }
  
  .menu {
    display: flex;
    position: relative;
    background: rgba(255, 255, 255, 0.2);
    border-radius: 10px;
    padding: 20px 20px;
   
  }
  
  .menu a {
    position: relative;
    padding: 12px 20px;
    margin: 0 5px;
    color: #002147;
    text-decoration: none;
    font-weight: 600;
    transition: color 0.3s ease;
  }
  
  .menu a:hover {
    color: #f58220;
  }
   /* ===== Phần nội dung chính ===== */
    .container {
      max-width: 900px;
      margin: 60px auto;
      background: rgba(255, 255, 255, 0.9);
      padding: 40px 50px;
      border-radius: 15px;
      box-shadow: 0 8px 25px rgba(0, 0, 0, 0.1);
      animation: slideUp 0.8s ease;
    }

    @keyframes slideUp {
      from {transform: translateY(40px); opacity: 0;}
      to {transform: translateY(0); opacity: 1;}
    }

    h1 {
      text-align: center;
      color: #003366;
      margin-bottom: 20px;
      font-size: 2.2em;
    }

    p {
      text-align: center;
      color: #333;
      margin-bottom: 30px;
    }

    /* ===== Form trả sách ===== */
    form {
      display: flex;
      flex-direction: column;
      gap: 20px;
    }

    label {
      font-weight: 600;
      color: #003366;
    }

    input, select, textarea {
      padding: 12px 14px;
      border: 1.5px solid #aac4ff;
      border-radius: 8px;
      font-size: 15px;
      outline: none;
      transition: all 0.3s ease;
    }

    input:focus, select:focus, textarea:focus {
      border-color: #0066ff;
      box-shadow: 0 0 6px rgba(51,170,255,0.5);
    }

    textarea {
      resize: none;
    }

    button {
      padding: 12px 0;
      background: linear-gradient(to right,#ff5100, #a7fd1c);
      color: white;
      font-weight: bold;
      border: none;
      border-radius: 8px;
      cursor: pointer;
      transition: transform 0.2s, box-shadow 0.2s;
    }

    button:hover {
      transform: translateY(-2px);
      box-shadow: 0 4px 10px rgba(51,170,255,0.4);
    }

    /* ===== Footer ===== */
    footer {
      text-align: center;
      padding: 20px 0;
      color: #003366;
      font-size: 14px;
      opacity: 0.8;
    }

    /* ===== Hiệu ứng nền chuyển động ===== */
    .background {
      position: absolute;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
    
      animation: moveBackground 20s infinite linear;
      z-index: -1;
    }

    @keyframes moveBackground {
      from {background-position: 0 0;}
      to {background-position: 100% 100%;}
    }