Bootstrap summary (a) grid system

    1. Direct the bootstrap 4 
           

<div class="row">
            <div class="col-md-4 col-sm-3 col-lg-2">                
                <img src="images/logos.png" alt="" />
            </div>
</div>

           col-lg-2 ≥992px large screen display 6 
          col-md-3 ≥768px medium screen display 4 by the general
          col-sm-4 ≥576px three plates placed

         Can be placed together 

.col- for all devices 
.col-sm- plates - greater than or equal to the screen width 576px 
.col-the MD-table display - greater than or equal to the screen width 768px) 
.col-table display LG- large - greater than or equal to the screen width 992px) 
.col-xl- table display large - greater than or equal to the screen width 1200px)

　　

2. pull-right    

    Floating around

3
.page-header underlined 
lead