/* @import url('http://example.com/example_style.css'); */

/***********************************************/
/* CSS @imports must be at the top of the file */
/* Add them above this section                 */
/***********************************************/

/*****************************************/
/* Start your style declarations here    */
/*****************************************/

<style>
  /* Responsive Google Slides, YouTube & Vimeo */
iframe[src*="docs.google.com"],
iframe[src*="youtube.com"],
iframe[src*="player.vimeo.com"]{
  width: 100%;
  height: auto;
  aspect-ratio: 16 / 9;
}
</style>