Edit in JSFiddle


              
<div class="wrapper">
    <div class="h_iframe">
        <!-- a transparent image is preferable -->
        <img class="ratio" src="http://placehold.it/16x9"/>
        <iframe src="https://itinerary.friendstravelvietnam.com/trip/ggrx6jw3havk7kexyavw6mux7afq" frameborder="0" allowfullscreen></iframe>
    </div>
    <p>Organized by Friends Travel Vietnam.</p>
</div>
html,body        {height:100%;}
.wrapper         {width:80%;height:100%;margin:0 auto;background:#CCC}
.h_iframe        {position:relative;}
.h_iframe .ratio {display:block;width:100%;height:auto;}
.h_iframe iframe {position:absolute;top:0;left:0;width:100%; height:100%;}