Hi. You can tell me where to insert CSS:
<pre style="margin-top: 0px; margin-bottom: 15px; padding: 10px; overflow-x: auto; font-stretch: normal; font-size: 12px; line-height: normal; font-family: Monaco, monospace; color: #000000; background: #eeeeee;"><code style="margin: 0px; padding: 0px;">video {
width: 100% !important;
height: auto !important;
}
for all youtube videos are responsive on the website?
For adding custom css you can either add it in appearance->customize->custom css OR in the style.css file of the child theme (if using a child theme).
For making the video responsive you can use [iframe] or [iframevideo] shortcode like:
[iframevideo]...Here your iframe video embedded url...[/iframevideo]