Equal Height Children of Grid Items

Equal height children of grid items

Unless you can use display: subgrid or display: contents (more info below), the only way to achieve this behavior with CSS alone would be to put all children of the various grid items in a single grid container. In other words, make them all siblings.

The problem is that an element in one container has no idea what its cousin in another container is doing. They have no direct connection, which prevents them from working together. Siblings, on the other hand, have no problem working together.

Note that "flattening" HTML documents for the purposes of CSS is not recommended as it damages semantics and accessibility.

More information:

Positioning content of grid items in primary container (subgrid feature)
What is an alternative to css subgrid?

Equal height of elements inside grid item with CSS grid layout

Is it even possible?

tldr; Yes.

Codepen Demo #1

Codepen Demo # 2 (Uses SASS and is configurable)

The difficulty here is that each article is a grid within itself and therefore any one article has no knowledge about another. Because of this, there is no way for a component of one article like a header to adjust according to the height of a header in another article.

There is actually a way to pull this off with css grids & without changing any markup!

We could 'flatten' the structure with CSS such that all the components of all the articles are part of just one CSS grid - the article container.

This is possible without even changing the current markup by setting the articles with display: contents

display: contents (caniuse)

From Caniuse:

display: contents causes an element's children to appear as if they
were direct children of the element's parent, ignoring the element
itself. This can be useful when a wrapper element should be ignored
when using CSS grid or similar layout techniques.

So if we set the articles with display: contents

.container article {
  display: contents;
}

Now all of the headers, sections and footer become (direct) grid items (of the container - which has display:grid) which we can arrange using the grid-template-areas property.

.container {
  display: grid;
  grid-column-gap: 1em; /* horizontal gap between articles */
  grid-template-columns: repeat(3, 1fr);

  grid-template-areas: "header1 header2 header3" 
                       "section1 section2 section3"
                       "footer1 footer2 footer3"
                       "header4 header5 header6" 
                       "section4 section5 section6"
                       "footer4 footer5 footer6"
}

Since each header/section/footer take up exactly one cell - this forces them to take up the same vertical height. So e.g. header1,header2 and header3 will all have the same height regardless of their content.

Now set the grid-area properties on each of the cells.

article:nth-child(1) header {
  grid-area: header1;
}
article:nth-child(2) header {
  grid-area: header2;
}
article:nth-child(3) header {
  grid-area: header3;
}
article:nth-child(4) header {
  grid-area: header4;
}
article:nth-child(1) section {
  grid-area: section1;
}
...
article:nth-child(4) section {
  grid-area: section4;
}
article:nth-child(1) footer {
  grid-area: footer1;
}
...
article:nth-child(4) footer {
  grid-area: footer4;
}

Finally, set a vertical gap between each row of articles (starting from the second row of articles):

article:nth-child(n + 4) header {
  margin-top: 1em;
}

Demo:

body {

  width: 100%;

  max-width: 1024px;

  margin: auto;

}

.container {

  display: grid;

  grid-column-gap: 1em;

  grid-template-columns: repeat(3, 1fr);

  grid-template-areas: "header1 header2 header3" 

                      "section1 section2 section3"

                        "footer1 footer2 footer3"

                        "header4 header5 header6" 

                      "section4 section5 section6"

                        "footer4 footer5 footer6"

}

.container article {

  display: contents;

}

article header {

  background-color: #eeeeee;

}

article section {

  background-color: #cccccc;

}

article footer {

  background-color: #dddddd;

}

article:nth-child(n + 4) header {

  margin-top: 1em;

}

article:nth-child(1) header {

  grid-area: header1;

}

article:nth-child(2) header {

  grid-area: header2;

}

article:nth-child(3) header {

  grid-area: header3;

}

article:nth-child(4) header {

  grid-area: header4;

}

article:nth-child(1) section {

  grid-area: section1;

}

article:nth-child(2) section {

  grid-area: section2;

}

article:nth-child(3) section {

  grid-area: section3;

}

article:nth-child(4) section {

  grid-area: section4;

}

article:nth-child(1) footer {

  grid-area: footer1;

}

article:nth-child(2) footer {

  grid-area: footer2;

}

article:nth-child(3) footer {

  grid-area: footer3;

}

article:nth-child(4) footer {

  grid-area: footer4;

}

<div class="container">

    <article>

        <header>

            <h2>Header</h2>

            <h2>Header</h2>

        </header>

        <section>

            <p>Content</p>

        </section>

        <footer>

            <p>Footer</p>

        </footer>

    </article>

    <article>

        <header>

            <h2>Header</h2>

        </header>

        <section>

            <p>Content</p>

            <p>Content</p>

            <p>Content</p>

            <p>Content</p>

            <p>Content</p>

        </section>

        <footer>

            <p>Footer</p>

            <p>Footer</p>

        </footer>

    </article>

    <article>

        <header>

            <h2>Header</h2>

        </header>

        <section>

            <p>Content</p>

            <p>Content</p>

            <p>Content</p>

        </section>

        <footer>

            <p>Footer</p>

        </footer>

    </article>

    <article>

        <header>

            <h2>Header</h2>

        </header>

        <section>

            <p>Content</p>

            <p>Content</p>

            <p>Content</p>

            <p>Content</p>

        </section>

        <footer>

            <p>Footer</p>

            <p>Footer</p>

        </footer>

    </article>

</div>

How to make every grid item the same width/height when one of them has an image child?

Focusing on the image

.mainContainer img{
  height: 30px; // set it to any size
  object-fit: contain;
}

I think you should use px instead of %

Sample Image

@mui grid items of equal height

Please use this code from the box downwards. You can read more about how to work with grid items on the mui website here.

const StackOverflow = () => {
  const createTable = (rows) => {
    return (
      <Table>
        <TableBody>
          {[...Array(rows).keys()].map((n) => {
            return (
              <TableRow key={n}>
                <TableCell>Aaaaa</TableCell>
              </TableRow>
            );
          })}
        </TableBody>
      </Table>
    );
  };
  return (
    <Box p={3}>
      <Container maxWidth="sm">
        <Grid container spacing={2}>
          <Grid item xs={6}>
            <Paper elevation={3} sx={{ p: 3, height: "100%" }}>
              <Typography variant="h4">Something</Typography>
              {createTable(5)}
            </Paper>
          </Grid>
          <Grid item xs={6}>
            <Paper elevation={3} sx={{ p: 3, height: "100%" }}>
              <Typography variant="h4">More things</Typography>
              {createTable(3)}
            </Paper>
          </Grid>
        </Grid>
      </Container>
    </Box>
  );
};

Set grid items to be same height

You can add more rows like this:

grid-template: ".   two   ." 1fr
               "one two  three" 1fr
               "one four three" 1fr
               ".   four  ." 1fr / 
               1fr  1fr  1fr;

With the appropriate grid-area on children.

Here is the snippet (I have also added a height: 90%; on children to make them fit the cells height but keeping the margin):

#cards {
  padding: 0 7vw;
  margin-top: 3vh;
  display: grid;
  grid-template: ".   two  ." 1fr
                 "one two three" 1fr
                 "one four three" 1fr
                 ".   four  ." 1fr / 
                 1fr  1fr  1fr;
  align-items: center;
  justify-content: center;
}

.card:nth-child(1){
  grid-area: one;
}
.card:nth-child(2){
  grid-area: two;
}
.card:nth-child(3){
  grid-area: three;
}
.card:nth-child(4){
  grid-area: four;
}

.card {
  display: block;
  border: solid 5px #000;
  box-shadow: 0 20px 30px -15px hsl(215, 49%, 82%);
  border-radius: 8px;
  margin: 5%;
  overflow: hidden;
  text-align: center;
  height: 90%;
}

<div id="cards">
  <div class="card">
    <div class="card-content">
      <h2 class="card-title">Item 1</h2>
    </div>
  </div>
  <div class="card">
    <div class="card-content">
      <h2 class="card-title">Item 2</h2>
    </div>
  </div>
  <div class="card">
    <div class="card-content">
      <h2 class="card-title">Item 3</h2>
      <p>Hello world</p>
    </div>
  </div>
  <div class="card">
    <div class="card-content">
      <h2 class="card-title">Item 4</h2>
      <p>I built this two line paragraph oh yes I really want it to be two lines or yes finally.</p>
    </div>
  </div>
</div>

Making the content inside grid items equal height in CSS Grid

Those grid items are already the same height. They are both the height of the second row, which is 1fr, as defined by grid-template-rows on the grid container.

If you put a border around those two items (.companyInfoContainer & .contactInfoContainer), you'll see what I mean.

revised demo

It seems that you want the bordered children of the grid items (.companyInfoBox and .contactInfoBox) to consume all available height.

Since the grid items are not also grid containers, you can't use grid properties on the children.

An easy and efficient solution would be to make the grid items flex containers. Then you can apply flex properties to the children, which can make them consume free space.

.companyInfoContainer {
   display: flex;
   flex-direction: column;
}

.companyInfoBox {
   flex: 1;
 }

.contactInfoContainer {
  display: flex;
  flex-direction: column;
}

.contactInfoBox {
   flex: 1
}

revised demo

More details: Descendant element not responding to grid properties

Equal height rows in CSS Grid Layout

Short Answer

If the goal is to create a grid with equal height rows, where the tallest cell in the grid sets the height for all rows, here's a quick and simple solution:

Set the container to grid-auto-rows: 1fr

How it works

Grid Layout provides a unit for establishing flexible lengths in a grid container. This is the fr unit. It is designed to distribute free space in the container and is somewhat analogous to the flex-grow property in flexbox.

If you set all rows in a grid container to 1fr, let's say like this:

grid-auto-rows: 1fr;

... then all rows will be equal height.

It doesn't really make sense off-the-bat because fr is supposed to distribute free space. And if several rows have content with different heights, then when the space is distributed, some rows would be proportionally smaller and taller.

Except, buried deep in the grid spec is this little nugget:

7.2.3. Flexible Lengths: the fr
unit

...

When the available space is infinite (which happens when the grid
container’s width or height is indefinite), flex-sized (fr) grid tracks are
sized to their contents while retaining their respective proportions.

The used size of each flex-sized grid track is computed by determining
the max-content size of each flex-sized grid track and dividing that
size by the respective flex factor to determine a “hypothetical 1fr
size”.

The maximum of those is used as the resolved 1fr length (the
flex fraction), which is then multiplied by each grid track’s flex
factor to determine its final size.

So, if I'm reading this correctly, when dealing with a dynamically-sized grid (e.g., the height is indefinite), grid tracks (rows, in this case) are sized to their contents.

The height of each row is determined by the tallest (max-content) grid item.

The maximum height of those rows becomes the length of 1fr.

That's how 1fr creates equal height rows in a grid container.

Why flexbox isn't an option

As noted in the question, equal height rows are not possible with flexbox.

Flex items can be equal height on the same row, but not across multiple rows.

This behavior is defined in the flexbox spec:

6. Flex Lines

In a multi-line flex container, the cross size of each line is the minimum size necessary to contain the flex items on the line.

In other words, when there are multiple lines in a row-based flex container, the height of each line (the "cross size") is the minimum height necessary to contain the flex items on the line.

Equal Height Children of Grid Items