Use :nth-child(odd) {clear:both;}
Working demo
CSS
.outer {border:solid #f00; padding:10px;overflow:auto} .outer div{border:solid 1px #f00; float:left; margin:5px} .outer div:nth-child(odd) {clear:both;}
HTML
<div class="outer"> <div > content content content content <br>content content content content <br>content content content content <br>content content content content <br>content content content content <br>content content content content <br></div> <div > content content content content <br>content content content content <br>content content content content <br> </div> <div > content content content content <br>content content content content <br>content content content content <br>content content content content <br>content content content content <br>content content content content <br> </div> <div> content content content content <br>content content content content <br>content content content content <br>content content content content <br>content content content content <br>content content content content <br> </div> <div > content content content content <br>content content content content <br>content content content content <br>content content content content <br>content content content content <br>content content content content <br> </div> </div>
source share