nav.html

<nav class="navbar navbar-expand-lg">
  <button
    class="navbar-toggler"
    type="button"
    data-toggle="collapse"
    data-target="#navbarSupportedContent"
    aria-controls="navbarSupportedContent"
    aria-expanded="false"
    aria-label="Toggle navigation"
  >
    <span class="navbar-toggler-icon"></span>
  </button>

  <div class="collapse navbar-collapse" id="navbarSupportedContent">
    <ul class="navbar-nav mr-auto">
      <li class="nav-item">
        <a class="nav-link" href="index.html"
          >Home <span class="sr-only">(current)</span></a
        >
      </li>

      <li class="nav-item dropdown">
        <a
          class="nav-link dropdown-toggle"
          href="#"
          id="navbarDropdown"
          role="button"
          data-toggle="dropdown"
          aria-haspopup="true"
          aria-expanded="false"
        >
          #
        </a>
        <div class="dropdown-menu" aria-labelledby="navbarDropdown">
          <a class="dropdown-item" href="#/# as doctor.html"
            ># as Doctor</a
          >
          <a class="dropdown-item" href="#/# as patient.html"
            ># as Patient</a
          >
        </div>
      </li>
      <li class="nav-item dropdown">
        <a
          class="nav-link dropdown-toggle"
          href="#"
          id="navbarDropdown"
          role="button"
          data-toggle="dropdown"
          aria-haspopup="true"
          aria-expanded="false"
        >
          Log In
        </a>
        <div class="dropdown-menu" aria-labelledby="navbarDropdown">
          <a class="dropdown-item" href="login/# as doctor.html"
            >LogIn as Doctor</a
          >
          <a class="dropdown-item" href="login/#/# as patient.html"
            >LogIn as Patient</a
          >
        </div>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="appointment 1.php">Book An Appointment</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="list of doctors.php">Doctors Here!</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="index.html#contact">Contact Us</a>
      </li>
    </ul>
  </div>
</nav>

<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js"></script>