Question: My code igniter application works fine in my PC , Laptop(browser IE11), and mobile also. But in my tablet sessions are not working. My session code are

```
$sess_array = array();
$sess_array = array(
     'id' => $row->id,
     'username' => $row->username,
     'role' => $row->role
   );
$this->session->set_userdata('logged_in', $sess_array);
$session_data = $this->session->userdata('logged_in');
$data['username'] = $session_data['username'];
$data['role'] = $session_data['role'];

```

Answer: 
Use `100vh` for your `.container` height

```css
* {
  margin: 0;
  padding: 0;
}
.top_nav {
  height: 80px;
  width: 100%;
  background: rgba(0, 0, 0, .5);
  position: absolute;
}
.container {
  height: 100vh;
  width: 100%;
  max-width: 100%;
  overflow: hidden;
  background-image: url("http://cdn.pcwallart.com/images/beautiful-nature-animals-wallpaper-3.jpg");
  background-attachment: fixed;
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
  z-index: -1;
}
.details {
  height: 638px;
  width: 100%;
  background-color: #00e5de;
}
```

```html
<header>
  <div class="top_nav">

  </div>
</header>
<div class="container">
  <div id="short-des">

  </div>
</div>
<div class=details>
</div>
```

vh: hundredths of the viewport height.
All you have to do is expand the height of the container. You can use the vh sizing unit (hundredths of viewport height) or any other unit.