Ensure float elements indicate their size to the parent div. Add the clearfix class to the parent div

clearfix.css

.clearfix:after {
    visibility: hidden;
    display: block;
    font-size: 0;
    content: " ";
    clear: both;
    height: 0;
}

.clearfix {display: inline-block;}

/* Hides from IE-mac \*/
* html .clearfix {height: 1%;}
.clearfix {display: block;}
/* End hide from IE-mac */