How to make CSS grid container keep responsive square size?

Question

I want grid container to maintain square shape. So when screen is resized, it will get bigger or smaller, but it's height will be always same as it's width. I want to place 3 images inside, with top one taking up two columns, and bottom ones are square taking one column each.

HTML:

<div class='container'>
    <div class='grid'>
        <img></img>
        <img></img>
        <img></img>
    </div>
</div>

SASS:

.container: {
  background: #fff;
  max-width: 600px;
  padding: 10px;
}

.grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  grid-template-rows: 1fr 1fr;
  gap: 10px;

  & > img:first-child {
    grid-column: 1 / span 2;
    grid-row: 1;
  }

  img {
    width: 100%;
    background-color: #000;
    object-fit: cover;
  }
}

I tried adding pseudo element to grid to maintain square ratio, only to find out that it won't work for grid. I tried giving img height: 100% but it made the too long.

I found some questions about how to keep images inside square, but non of them was about how to keep grid container square and prevent from being stretched out by children.

Answer 1

I'd do the following:

1. Make the grid width and height responsively sized - for this use this method (.container and &::after pseudo element)
2. Make the grid itself follow the square width and height of the container (.grid-wrapper)
3. Use a container for the images, so that the containers resize inside the grid (1st row = 2 col wide, 2nd row = 2x1 col) (.grid-box)
4. Use absolute positioned images in the divs, so they actually cover the divs

HTML code:

<div class='container'>
  <div class='grid-wrapper'>
    <div class='grid'>
      <div class="grid-box">
        <img src="https://picsum.photos/200/300"></img>
      </div>
      <div class="grid-box">
        <img src="https://picsum.photos/200/300"></img>
      </div>
      <div class="grid-box">
        <img src="https://picsum.photos/200/300"></img>
      </div>
    </div>
  </div>
</div>

SASS code:

$-gutter: 10px;
$-max-width: 600px;

* {
  box-sizing: border-box;
}

.container {
  position: relative;
  max-width: $-max-width;
  width: 100%;
  background: #ffff00;

  &::after {
    content: "";
    display: block;
    padding-bottom: 100%;
  }
}

.grid-wrapper {
  position: absolute;
  width: 100%;
  height: 100%;
  padding: $-gutter;
}

.grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  grid-template-rows: 1fr 1fr;
  gap: $-gutter;
  width: 100%;
  height: 100%;

  &-box {
    position: relative;
    width: 100%;
    height: 100%;

    &:first-child {
      grid-column: 1 / span 2;
    }
  }

  img {
    position: absolute;
    width: 100%;
    height: 100%;
    background-color: #000000;
    object-fit: cover;
  }
}

Here is a Fiddle demo: https://jsfiddle.net/robertp/uLfj1swm/

And a screenshot of how this solution renders: