Скачать или смотреть Understanding box-sizing: border-box in CSS: Why Isn't It Working?

Discover why `box-sizing: border-box` may not function as expected in your CSS layouts and learn effective solutions to resolve common issues.
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This video is based on the question https://stackoverflow.com/q/64347272/ asked by the user 'Mostafa Fotouhi' ( https://stackoverflow.com/u/13522092/ ) and on the answer https://stackoverflow.com/a/64347482/ provided by the user 'MaxiGui' ( https://stackoverflow.com/u/11044542/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding box-sizing: border-box in CSS: Why Isn't It Working?

Have you ever encountered a situation where the CSS property box-sizing: border-box doesn't seem to work the way you expect? You're not alone! This is a common problem that many developers face, especially when dealing with padding and borders in their layouts. In this guide, we'll break down this issue, clarify why it happens, and provide practical solutions to make sure your layouts behave as intended.

The Problem Explained

Consider the following CSS snippet:

[[See Video to Reveal this Text or Code Snippet]]

And the corresponding HTML:

[[See Video to Reveal this Text or Code Snippet]]

In this scenario, we set our .box to have a height of 100 pixels, but you're probably noticing that the padding and border are not being calculated correctly. Specifically, why does the padding seem to apply only from the top and left sides?

Why Padding Isn't Applied Properly

The box-sizing: border-box property was designed to include padding and borders in the total width and height of elements. But, in the example above, we face a conflicting setup:

Height Issue: We specify a height of 100px.

Added Dimensions: The total heights contributed by the elements inside the box:

Border: 40px (top) + 40px (bottom) = 80px

Padding: 20px (top) + 20px (bottom) = 40px

Total: 80px + 40px = 120px

Thus, the total height needed exceeds the specified height of 100px. The browser attempts to make adjustments, but it may lead to unexpected results, such as padding only appearing on one side.

Effective Solutions

To tackle this issue effectively, here are a couple of practical adjustments you can make:

1. Adjust the Box Height

Instead of setting a fixed height, you can use min-height and height: auto; which allows the box to grow based on its content without exceeding the total number of pixels you initially intended.

[[See Video to Reveal this Text or Code Snippet]]

2. Test the Output

Always check how your layout behaves in a live environment. Here is the demo:

[[See Video to Reveal this Text or Code Snippet]]

This will now display correctly with the padding and border accounted for, giving you a proper visual representation in your layout.

Conclusion

Understanding how box-sizing: border-box operates can save you a significant amount of time and frustration when designing your web layouts. Always remember that when combining height, padding, and borders, they must fit within your specified dimensions so that your design renders as expected.

By applying the recommended solutions, you can have a robust CSS setup that scales well and maintains a proper layout across devices. Happy coding!