Responsive CSS Grid with persistent aspect ratio

Question

My goal is to create a responsive grid with an unknown amount of items, that keep their aspect ratio at 16 : 9. Right now it looks like this:

Answer 1

You could take advantage of the fact that padding in percentages is based on width.

This CSS-tricks article explains the idea quite well:

...if you had an element that is 500px wide, and padding-top of 100%, the padding-top would be 500px.

Isn't that a perfect square, 500px × 500px? Yes, it is! An aspect ratio!

If we force the height of the element to zero (height: 0;) and don't have any borders. Then padding will be the only part of the box model affecting the height, and we'll have our square.

Now imagine instead of 100% top padding, we used 56.25%. That happens to be a perfect 16:9 ratio! (9 / 16 = 0.5625).

So in order for the columns to maintain aspect ratio:

1) Set the column widths as you suggested:

grid-template-columns: repeat(auto-fit, minmax(160p, 1fr))

2) Add a pseudo element to the items to maintain the 16:9 aspect ratio:

.item:before {
  content: "";
  display: block;
  height: 0;
  width: 0;
  padding-bottom: calc(9/16 * 100%);
}

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  grid-template-rows: 1fr;
  grid-gap: 20px;
}
.item {
  background: grey;
  display: flex;
  justify-content: center;
}
.item:before {
  content: "";
  display: block;
  height: 0;
  width: 0;
  padding-bottom: calc(9/16 * 100%);
}

Codepen Demo (Resize to see the effect)