header.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>
		    <form action="validacionuser.php" class="form-inline my-2 my-lg-0">
		      <input class="form-control mr-sm-2" type="text" placeholder="Usuario" >
		      <input class="form-control mr-sm-2" type="password" placeholder="Contraseña">
		      <button class="btn btn-success my-2 my-sm-0" type="submit">Entrar</button>
		    </form>

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