.video-block {
   width: 100%;
   max-width: 700px;
   margin-left: auto; margin-right: auto;
   margin-bottom: 50px;
}
.youtube-wrapper {
   height: 0;
   position: relative;
   margin-bottom: 10px;
   padding-top: 25px;
   padding-bottom: 56.25%; /* 16:9 */
}
.youtube-wrapper iframe {
   position: absolute; top: 0; left: 0;
   width: 100%; height: 100%;
}