bootstrap on website issue

I think for your mobile web just use col-xs-xx. If you use same view for www. & m. version you can have both in. Example <div class="col-xs-12 col-sm-6">A</div> <div class="col-xs-12 col-sm-6">B</div>
In less than 768px width screen the B will push bottom. While in 768px and above B position is beside A. col-xx-cc, xx option xs,sm,md,lg & cc max value 12.

Keep calm.