In a bootstrap responsive page how to center a div

CSS:

html,
body {
    height: 100%;
}

.container {
    height: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
}

HTML:

<div class="container">
  <div>
    example
  </div>
</div>

Example fiddle


Update for Bootstrap 5

Simpler vertical grid alignement with flex-box

@import url('https://cdnjs.cloudflare.com/ajax/libs/bootstrap/5.0.1/css/bootstrap.min.css');
html,
body {
  height: 100%
}
<div class="h-100 d-flex align-items-center justify-content-center">
  <div style="background:red">
    TEXT
  </div>
</div>

Solution for Bootstrap 4

Simpler vertical grid alignement with flex-box

@import url('https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css');
html,
body {
  height: 100%
}
<div class="h-100 d-flex align-items-center justify-content-center">
  <div style="background:red">
    TEXT
  </div>
</div>

Solution for Bootstrap 3

@import url('http://getbootstrap.com/dist/css/bootstrap.css');
 html, body, .container-table {
    height: 100%;
}
.container-table {
    display: table;
}
.vertical-center-row {
    display: table-cell;
    vertical-align: middle;
}
<script src="http://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/2.1.0/bootstrap.min.js"></script>

<div class="container container-table">
    <div class="row vertical-center-row">
        <div class="text-center col-md-4 col-md-offset-4" style="background:red">TEXT</div>
    </div>
</div>

It's a simple example of a horizontally and vertically div centered in all screen sizes.