test page
<html><head><meta name="viewport" content="width=device-width, initial-scale=1" /><style> * { box-sizing: border-box; } .column { float: left; width: 33.33%; padding: 10px; height: 370px; .row:after { content: ""; display: table; clear: both; } </style></head><body> <h2></h2> <div class="row"> <div class="column" style="background-color:#2DCB44;"> <h2><iframe width="99.33%;" height="315" src="https://www.youtube.com/embed/JGzU_l5H1lE" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen=""></iframe></h2> <p></p> </div> <div class="column" style="background-color:#29B33D;"> <h2><iframe width="99.33%;" height="315" src="https://www.youtube.com/embed/4ujuPIioH6M" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen=""></iframe></h2> <p></p> </div> <div class="column" style="background-color:#239934;"> <h2><iframe width="99.33%;" height="315" src="https://www.youtube.com/embed/2O9ZK2Fd_aU" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen=""></iframe></h2> <p></p> </div> </div> </body></html>