How to center div with col-md-6?

Bootstrap 3

Add the col-md-offset-3 class that will offset by 3 columns, given that Bootstrap has a 12-column grid this will put a col-md-6 element right in the center.

Documentation reference on offsets.

Bootstrap 4

Use offset-3 or mx-auto to center a col-md-6 column

Just add "float:none;margin:auto;" to your div style like this :

<div class="col-lg-6" style="float:none;margin:auto;">
   .....
</div>

Hope to be useful ;)