wcfsetup/install/files/style/bbcode/video.scss

   1 /* scale embedded videos to maximum width */
   2 .videoContainer {
   3         display: block;
   4         overflow: hidden;
   5         padding-bottom: 56.25%; /* 9 / 16 */
   6         position: relative;
   7         text-align: left;
   8
   9         iframe,
  10         video {
  11                 height: 100%;
  12                 position: absolute;
  13                 width: 100%;
  14         }
  15 }