body {
      margin: 0;
      font-family: Arial, sans-serif;
    }

    header {
      background: #1d232a;
      color: white;
      padding: 10px 20px;
      display: flex;
      justify-content: space-between;
      align-items: center;
      position: relative;
    }

    .logo {
      display: flex;
      align-items: center;
    }

    .logo img {
      height: 40px;
    }

    .hamburger {
      font-size: 28px;
      cursor: pointer;
      display: block;
    }

    nav {
      background-color: #3c4754;
      max-height: 0;
      overflow: hidden;
      transition: max-height 0.5s ease;
    }

    nav ul {
      list-style: none;
      padding: 0;
      margin: 0;
    }

    nav li {
      border-top: 1px solid #4e5967;
      position: relative;
    }

    nav li a {
      display: block;
      padding: 14px 20px;
      text-decoration: none;
      color: #ffffff;
      font-weight: bold;
      position: relative;
    }

    nav li a .arrow {
      float: right;
      transition: transform 0.3s ease;
    }

    nav li ul {
      background-color: #505c6c;
      max-height: 0;
      overflow: hidden;
      transition: max-height 0.4s ease;
    }

    nav li.open > ul {
      max-height: 500px;
    }

    nav li.open > a .arrow {
      transform: rotate(90deg);
    }

    .menu-open {
      max-height: 1000px;
    }