.youtubeemb{position:relative;max-width:800px;width:100%;height:0;margin:0 auto;padding-top:56.25%}.youtubeemb iframe{position:absolute;left:0;top:0;width:100%;height:100%}body{text-align:justify}.centerimg{text-align:center}.centerimg img{max-width:100%}h1,h2,h3{text-align:center;margin:20px}h1{margin:20px 0 30px}h2,h3{margin:20px}