Similar to flexbox, CSS grid has a default minimum content size for its child items which is auto. That means, if there is an element that is larger than the grid item, it will overflow.

In the example above, we have a carousel within the main section. For context, here is the HTML and CSS.

<div class="wrapper">
    <main>
        <section class="carousel"></section>
    </main>
    <aside></aside>
</div>

@media (min-width: 1020px) {
    .wrapper {
        display: grid;
        grid-template-columns: 1fr 248px;
        grid-gap: 40px;
    }
}
.carousel {
    display: flex;
    overflow-x: auto;
}

Since the carousel is a flex container that doesn’t wrap, its width is larger than the main section, and thus the grid item respected that. As a result, there is horizontal scrolling.

To fix that, we have three different solutions:

• Using minmax()
• Applying min-width to the grid item
• Adding overflow: hidden to the grid item

As a defensive CSS mechanism, it doesn't matter which solution to pick, but for this example I will go with the min-width one.

I wrote about that in more detail. I also highly recommend checking "Preventing a Grid Blowout" and "You want minmax(10px, 1fr) not 1fr" by Chris Coyier.

Examples and use cases

Main and aside

Based on the previous illustrated demo, we have a page that contains a main and an aside sections. The main section has a scrollable element (a carousel).

<div class="page">
    <div class="page__item page__item--main">
        <div class="slider">
            <div class="slider__item"></div>
            <!-- more items -->
        </div>
    </div>
    <div class="page__item page__item--aside"></div>
</div>

.slider {
    display: flex;
}
.page {
    display: grid;
    grid-template-columns: 1fr 100px;
    grid-gap: 1rem;
}

The element .page__item--main is a grid item, and when the .slider doesn't wrap its child items, the main grid item will expand to fit all the slider items.

To overcome that, we can pick one of the solutions mentioned above. For this example, I will pick min-width: 0.

Try to click the "Toggle Defensive" option to see the solution in action.

.page__item--main {
    /* prevent the grid item from respecting the
    * minimum content size
    */
    min-width: 0;
}