Why Aren\'t My Flex Items Respecting Margins When Using `box-sizing: border-box`?

Flex Items Not Respecting Margins and Box-sizing: border-box

Understanding the concept of box-sizing and how it affects the behavior of flex items is crucial when using CSS Flexbox. By default, the box-sizing property is set to "content-box," which means that padding and borders are added to the content width and height. However, when box-sizing is set to "border-box," margins are not factored into the width or height calculations.

In this case, where flex items are encountering issues with margins and box-sizing set to "border-box," the cause lies in the disregard of margins when calculating item widths. The initial setting of flex containers is flex-shrink: 1, meaning that flex items can reduce their size to fit within the container. However, this by itself is insufficient to ensure adherence to specified widths, heights, or flex-basis unless flex-shrink is disabled.

Solution

To resolve the issue and ensure that flex items respect margins while using box-sizing: border-box, consider the following adjustment:

Replace:

<code class="css">flex: 1 1 33.33%;
margin: 10px;</code>

With:

<code class="css">flex: 1 0 26%;
margin: 10px;</code>

By reducing the flex-basis from 33.33% to 26%, it becomes small enough to force a wrap while still allowing the margin to be factored in. This adjustment ensures that flex items do not intrude into the margin space and adhere to the specified widths and margins.

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