Embedding YouTube videos into web pages is a common practice, but it's essential that the video adjusts correctly to various screen sizes. To achieve this, a responsive iframe can be used, ensuring that the video always looks good regardless of the device it's viewed on. Here's the code for a responsive YouTube iframe:

<div style="position: relative; padding-bottom: 56.25%; height: 0; overflow: hidden;">
    <iframe src="/
" style="position: absolute; top: 0; left: 0; width: 100%; height: 100%; border: 0;" allowfullscreen></iframe>
</div>

How does this code work?

• The <div> container holds the iframe and sets the aspect ratio for responsiveness.
• padding-bottom: 56.25%; sets the aspect ratio (16:9), allowing the iframe to adjust to the container's width.
• position: relative; maintains the relative position of the container, which is important for the iframe's position.
• position: absolute; allows the iframe to fill the entire space within the container.
• top: 0; left: 0; aligns the iframe to the top-left corner of the container.
• width: 100%; height: 100%; ensures the iframe occupies all available space inside the container.
• border: 0; removes borders from the iframe.
• allowfullscreen enables fullscreen mode for the embedded YouTube content if supported.

This code allows you to embed a YouTube video on your web page in a way that automatically adapts to the screen size, ensuring a good user experience regardless of the device the video is viewed on.