login.php

<?php
  error_reporting(0);
  $this->load->library('form_validation');
  echo form_open('login');
  ?>
  <div class="login container">
    <img class="icon" src="<?php echo base_url("img/twitter.png")?>" alt="Twitter">
    <div class="form-group">
        <label for="username">Username</label>
        <input class="form-control" type="text" name="username" value="<?php echo set_value('username'); ?>" placeholder="Enter username"/>
        <?php echo form_error('username'); ?>
    </div>
    <div class="form-group">
        <label for="password">Password</label>
        <input class="form-control" type="password" name="password" value="<?php echo set_value('password'); ?>" placeholder="Enter password"/>
        <?php echo form_error('password'); ?>
    </div>
    <button type="submit" class="btn btn-primary">Login</button><span> or <a href="register">Create an account</a></span>

    </form>

  </div>
  <script type="text/javascript" src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
</body>
</html>