why margin does not work in between div of 'bootstrap col'?

Question

http://bootply.com/84073

<div class"col-lg-12"="">
    <header class="clearfix">
        <section id="branding">
            <a href="index.php"><img src="https://www.google.com/images/srpr/logo4w.png" alt=""></a>
        </section>
  </header></div>

I tried to add #branding{margin: 0 auto} to style the logo to the middle, but it doesn't work

Answer 1

img {
  display: block;
  margin: 0 auto;
}

Should do the trick.

Answer 2

You can use

 #branding{text-align: center;}