Equal height rows in a flex container

Question

The answer is NO.

The reason is provided in the flexbox specification:

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 rows, however, are possible in CSS Grid Layout:

• Equal height rows in CSS Grid Layout

Otherwise, consider a JavaScript alternative.

You can accomplish that now with display: grid:

.list {
  display: grid;
  overflow: hidden;
  grid-template-columns: repeat(3, 1fr);
  grid-auto-rows: 1fr;
  grid-column-gap: 5px;
  grid-row-gap: 5px;
  max-width: 500px;
}
.list-item {
  background-color: #ccc;
  display: flex;
  padding: 0.5em;
  margin-bottom: 20px;
}
.list-content {
  width: 100%;
}

<ul class="list">
  <li class="list-item">
    <div class="list-content">
      <h2>box 1</h2>
      <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit.</p>
    </div>
  </li>
  <li class="list-item">
    <div class="list-content">
      <h3>box 2</h3>
      <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit.</p>
    </div>
  </li>

  <li class="list-item">
    <div class="list-content">
      <h3>box 2</h3>
      <p>Lorem ipsum dolor</p>
    </div>
  </li>

  <li class="list-item">
    <div class="list-content">
      <h3>box 2</h3>
      <p>Lorem ipsum dolor</p>
    </div>
  </li>
  <li class="list-item">
    <div class="list-content">
      <h1>h1</h1>
    </div>
  </li>
</ul>

Although the grid itself is not flexbox, it behaves very similar to a flexbox container, and the items inside the grid can be flex.

The grid layout is also very handy in the case you want responsive grids. That is, if you want the grid to have a different number of columns per row you can then just change grid-template-columns:

grid-template-columns: repeat(1, 1fr); // 1 column
grid-template-columns: repeat(2, 1fr); // 2 columns
grid-template-columns: repeat(3, 1fr); // 3 columns

and so on...

You can mix it with media queries and change according to the size of the page.

Sadly there is still no support for container queries / element queries in the browsers (out of the box) to make it work well with changing the number of columns according to the container size, not to the page size (this would be great to use with reusable webcomponents).

More information about the grid layout:

https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Grid_Layout

Support of the Grid Layout accross browsers:

https://caniuse.com/#feat=css-grid

You can with flexbox for horizontal issues:

.flex-list {
    padding: 0;
    list-style: none;
    display: flex;
    align-items: stretch;
    flex-wrap: wrap;
    justify-content: center;
    gap: .5rem;
}
.flex-list li {
    width: 100px;
    padding: .5rem;
    border-radius: 1rem;
    background: yellow;
    margin: 0 5px;
}

<ul class="flex-list">
  <li>title 1</li>
  <li>title 2</li>
  <li>title 3<br>new line</li>
  <li>title 4<br>new line</li>
  <li>title 5<br>new<br>line</li>
  <li>title 6</li>
</ul>

Or with grid for both horizontal and vertical issues:

.grid-list {
   padding: 0;
   list-style: none;
   display: grid;
   grid-auto-columns: 1fr;
   grid-auto-rows: 1fr;
   grid-template-columns: repeat(3, 1fr);
   gap: .5rem;
}
    
.grid-list li {
   padding: .5rem;
   border-radius: 1rem;
   background: yellow;
   margin: 0 5px;
}   

.grid-list li:last-child {
   grid-column-start: 2;
}  

<ul class="grid-list">
    <li>title 1</li>
    <li>title 2<br>new<br>line</li>
    <li>title 3<br>new line</li>
    <li>title 4<br>new line</li><li>title 5</li>
    <li>title 6<br>new<br>line</li>
    <li>title 7</li>
   </ul>

No, you can't achieve that without setting a fixed height (or using a script).

---

Here are 2 answers of mine, showing how to use a script to achieve something like that:

• How to get header from cards or similar to have the same height with flex box?

• Same height for flex items in the flex-direction column flex container

This seems to be working in cases with fixed parent height (tested in Chrome and Firefox):

.child {
        height    : 100%;
        overflow  : hidden;
}

.parent {
        display: flex;
        flex-direction: column;
        height: 70vh; // ! won't work unless parent container height is set
        position: relative;
}

If it's not possible to use grids for some reason, maybe it's the solution.