prueba2.php

<header>
      <nav class="navbar navbar-expand-lg navbar-light bg-light">
      <a class="navbar-brand" href="#">
        <img src="img/title.png" width="150" height="auto" alt="">
      </a>
      <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 actived">
            <a class="nav-link blanco" href="index.php">Home<span class="sr-only">(current)</span></a>
          </li>
          <li class="nav-item">
            <a class="nav-link blanco" href="preguntas.php">Question</a>
          </li>
          <li class="nav-item">
            <a class="nav-link blanco" href="contact.php">Contact</a>
          </li>
          <li class="nav-item">
            <a class="nav-link blanco" href="register.php">Register</a>
          </li>      
        </ul>
        <div class="btn-group">
          <button type="button" class="btn btn-secondary dropdown-toggle fuente" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
            ¿Ya tenes cuenta? <p>inicia sesion</p>
          </button>
          <div class="dropdown-menu fuente">
            <form class="px-4 py-3" action="validacionuser.php?pag=<?php echo $_SERVER['PHP_SELF']; ?>" method="POST">
              <div class="form-group"> 
                <input type="email" class="form-control" name="email" placeholder="Ingresa tu email" required>
              </div>
              <div class="form-group">
                <input type="password" class="form-control" name="password"  placeholder="Ingresa tu password" required>
              </div>
              <div class="form-group">
                <div class="form-check">
                  <input type="checkbox" class="form-check-input" id="dropdownCheck" name="recordar">
                  <label class="form-check-label" for="dropdownCheck">
                    Recordar usuario
                  </label>
                </div>
              </div>
              <input type="submit" class="btn btn-primary" value="Entrar">
            </form>
            <div class="dropdown-divider"></div>
            <a class="dropdown-item" href="recuperarpass.php">Olvide mi password</a>
          </div>
        </div>

      </div>
    </nav>
  </header>