Preventing Flexbox Children from Overflowing - Quick Guide

Flexbox is a powerful layout tool that simplifies the creation of responsive designs. It’s one of my favorite tools when structuring a web page or making sure that elements “flow” as expected. While this is a powerful weapon in a developer’s arsenal, it sometimes causes some confusion when the elements that should apparently fit a specific section of the parent’s width start growing out of control. If you’ve faced this issue before, here’s how to prevent it.

Before we take a deep dive into the various approaches I personally use to resolve this issue, it is important that I mention I tend to reset all my elements to have their box-sizing set to border-box. This is an important step as it ensures that padding and borders are included in the width and height calculations. As a result, cases of accidental overflow due to the padding pushing the element beyond it’s container’s dimensions are mostly none-existent. With that out of the way, let’s jump right into it.

Use min-width: 0 and max-width

Using the min-width property is one of the easiest and my favorite approach to tackling the child component width’s that just won’t behave issue. By default, setting display to flex on a parent container results in it’s child components getting the min-width property set to auto. As a result, if an element should rightfully shrink (per the size of your “flexed” parent), it immediately defaults to the auto minimum width which in turn prevents it from shrinking.

The solution in this case is therefore obvious since setting the minimum width communicates to the browser that the component has no right to take up a significant portion of the available width. This in turn defaults it to a width that is a fraction of what the flex parent is offering (i.e. 1/3 if you have three children on the parent container).

.flex-child {
	min-width: 0;
}

With the length explanation of min-width out of the way, max-width is a bit more direct (and in my opinion brute-force) approach to handling the issue. When using max-width one essentially informs the browser that the element should not take more than x width. While it certainly does the job, I don’t tend to use it much as it forces me to either decide on an appropriate width that also accounts for the gaps between the flex children or tends to leave things wanting especially if one child always tends to have a bit more content that the others. In this regard, while it does solve the issue, I’d still recommend going with min-width.

.flex-child {
	max-width: 33%;
}

Adding flex-shrink and flex-grow

flex-shrink and flex-grow properties (as their names imply) control how the flex-box children behave when space is either limited or abundant. In this regard, to prevent the children from surpassing their limits, one should set the flex-shrink and flex-grow properties to 0. With these settings, the flex items retain their size regardless of the surrounding content.

.flex-child {
	flex-shrink: 0;
	flex-grow: 0;
}

Setting the flex-basis

The flex-basis property allows one to define the default size of a flex item before the remaining space is distributed. In most cases, this is automatically calculated for you. However, in certain situations, one requires a bit more fine-grained control over what size a specific child should take. As such, when combined with the max-width property, one can better control the child’s size. An easy way to think of these two is - when you have set the flex-basis property, it controls what size the child would start at. However, once you add the max-width property, it defines how big the child can get given the starting point.

.flex-child {
	flex-basis: 100px; // Will start at 100px
	max-width: 200px; // Will not get past 200px
}

In certain situations, the content of the flex-box child might still overflow, despite setting the width constraints. In these cases, using the overflow property tends to do the trick. In addition, when dealing with text, setting the text-overflow and the white-space properties can also help you get that snug look.

Preventing flex-box children from overflowing or growing past their limit is essential for maintaining a clean and responsive design. In my case, it has allowed me to achieve that snug look without having text or other children elements encroaching on borders or the margin around flex-box children. The approaches supplied above will work for most situations. However, when one fails, you can always use another or try combining them in different approaches to see what results you might get. After all, discovery requires experimentation 😉.