The problem with embedding YouTube videos is that they are an iframe and iframes need to be given an exact height and width otherwise they will look funky.

And we need to keep the proportions, based on the video aspect ratio.

To have a YouTube video be displayed responsive in your page, first wrap it into a container div:

<div class="video-container">
  <iframe src="https://www.youtube.com/embed/...." frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
</div>

Then add this CSS to your site:

.video-container {
    overflow: hidden;
    position: relative;
    width:100%;
}

.video-container::after {
    padding-top: 56.25%;
    display: block;
    content: '';
}

.video-container iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}

See that magic number, 56.25%? That’s needed as a padding when the aspect ratio of a video is 16:9. (9 is 56.25% of 16).

If your video is 4:3 for example, set it to 75%.

Lessons in this unit:

0:	Introduction
1:	How to center an element with CSS
2:	CSS Border inside the element
3:	What are good CSS Breakpoint values for Responsive Design?
4:	How to debug CSS by bisecting
5:	How to disable text selection using CSS
6:	How to put an item at the bottom of its container using CSS
7:	CSS, how to select elements that do NOT have a class
8:	How to stick an element on the bottom of the page with flexbox
9:	How to apply padding to multiple lines in CSS
10:	Making a table responsive using CSS
11:	CSS url()
12:	How to make an element smaller or bigger with CSS
13:	Customizing visited links
14:	Fix extra space after inline element
15:	How to create a sidebar that’s sticky but also scrolls
16:	How to embed YouTube videos using the correct aspect ratio
17:	Responsive pre tags in CSS
18:	▶︎ Responsive YouTube Video Embeds
19:	How to remove all CSS from a page at once
20:	How I added Dark Mode to my website
21:	How to add a simple dark mode