aspect-ratio for embeds and placeholders
Only the width is known (240px); aspect-ratio works out the height. A real video <iframe> gets the same rule plus width: 100%. aspect-ratio: 1 is the same as 1 / 1.
Images and video are fixed-size by nature, so responsive pages tame them with CSS: max-width: 100%; height: auto stops overflow while keeping the shape, aspect-ratio reserves the right space, and object-fit/object-position decide how a picture fills a box of a different shape.
Change the code and press Run (Ctrl+Enter). Predict what will happen first, then break it on purpose and read what changes. Your edits are saved and match the lesson page.
Ready for more? This phase has 6 hands-on exercises with automatic checks.
Practice questions
Write the code in the editor, run it, then open the model answer to compare.
Write CSS so every image and video on a page is fluid, keeps its shape and has no gap underneath.
Make a gallery of square thumbnails from photos of any shape, keeping the top of each photo (people's heads) in view.
Make a map <iframe> that is full width and always 4:3.
Explain it without notes
Why do max-width: 100% and height: auto make images responsive?
How do the HTML width and height attributes help with layout shift, even for fluid images?
Compare object-fit: contain, cover and fill.
How would you make a YouTube <iframe> embed responsive?
Preview
Console
Nothing logged yet.Expected console output
video: 240 x 135
square: 240 x 240