The CSS property box-sizing is a powerful tool that allows you to control the size of elements on a web page.
By setting box-sizing: border-box, you can change the way that the size of an element is calculated, which can be especially useful for solving layout problems. In this article, we'll discuss what box-sizing: border-box does and what its advantages are.
CSS box model
In CSS, each element generates a box that represents its content. The size of this box is determined by the width and height properties, as well as the padding, border, and margin properties. The default value for the box-sizing property is content-box, which means that the size of an element's box is calculated based on its content only. In other words, the width and height of an element's box is equal to the width and height of its content, plus any padding and border.
However, the content-box value can cause layout problems, especially when you're working with elements that have padding or borders. For example, consider the following code:
.element {
width: 300px;
height: 200px;
padding: 20px;
border: 10px solid black;
}With a content-box value, the size of the element's box would be calculated as follows:
width: 300px (content width) + 20px (left padding) + 20px (right padding) + 10px (left border) + 10px (right border) = 360px (total width) height: 200px (content height) + 20px (top padding) + 20px (bottom padding) + 10px (top border) + 10px (bottom border) = 270px (total height)
As you can see, the width and height of the element's box is much larger than the specified width and height, which can cause layout problems.
This is where box-sizing: border-box comes in. By setting box-sizing: border-box, you can change the way that the size of an element's box is calculated. With a border-box value, the width and height of an element's box is equal to the specified width and height, plus any padding and border. In other words, the padding and border are included in the width and height of the element's box, which makes it easier to control the size of elements on a web page.
Here's an example of the same code as above, but with a border-box value:
.element {
box-sizing: border-box;
width: 300px;
height: 200px;
padding: 20px;
border: 10px solid black;
}With a border-box value, the size of the element's box would be calculated as follows:
width: 300px (specified width) + 20px (left padding) + 20px (right padding) + 10px (left border) + 10px (right border) = 300px (total width) height: 200px (specified height) + 20px (top padding) + 20px (bottom padding) + 10px (top border) + 10px (bottom border) = 200px (total height)
As you can see, the size of the element's box is now equal to the specified width and height, which makes it easier to control the layout of elements on a web page.
Responsive designs
Another advantage of using `box-sizing: border-box` is that it makes it easier to create responsive designs. When designing a responsive web page, you often need to adjust the size of elements based on the size of the viewport. With a `border-box` value, you can specify the size of an element based on its content, without having to worry about the size of its padding and border. This can make it easier to create designs that look great on all devices, regardless of the size of the viewport.
It's worth noting that `box-sizing: border-box` is a global setting, which means that it applies to all elements on a web page. If you want to use `border-box` for only some elements, you can use a CSS class to specify the setting for those elements:
.border-box {
box-sizing: border-box;
}
<div class="element border-box">...</div>Conclusion
In conclusion, box-sizing: border-box is a powerful CSS property that allows you to control the size of elements on a web page. By including the padding and border in the width and height of an element's box, border-box makes it easier to control the layout of elements and create responsive designs. Whether you're a seasoned web developer or just starting out, box-sizing: border-box is a valuable tool to have in your CSS toolkit.