CSS Box Sizing
CSS Box Sizing
The CSS box-sizing
property defines how to calculate the width and height of an element: should the
calculation include padding and borders, or not.
By default, the width and height of an element is calculated like this:
- width + padding + border = actual width of an element
- height + padding + border = actual height of an element
This means: When you set the width/height of an element, the element often appears bigger than you have set (because the element's border and padding are added to the element's specified width/height).
The following illustrates two <div> elements with the same specified width and height. The two <div> elements end up with different sizes (because div2 has a large padding specified):
Example
.div1 {
width: 300px;
height:
100px;
border: 1px solid blue;
}
.div2 {
width: 300px;
height: 100px;
padding: 50px;
border: 1px solid red;
}
Try it Yourself »
The box-sizing
property solves this problem.
The CSS box-sizing Solution
The box-sizing
property allows us to include the padding and border in
an element's total width and height.
If you set box-sizing: border-box;
on an element,
the padding and border are
included in the calculation of the width and height:
Here is the same example as above, with box-sizing: border-box;
added to both <div> elements:
Example
.div1 {
width: 300px;
height:
100px;
border: 1px solid blue;
box-sizing: border-box;
}
.div2 {
width: 300px;
height: 100px;
padding: 50px;
border: 1px solid red;
box-sizing: border-box;
}
Try it Yourself »
Since the result of using the box-sizing: border-box;
is so much better, many developers want all elements on their
pages to work this way.
The code below ensures that all elements are sized in this more intuitive way.
Many browsers already use box-sizing: border-box;
for
many form elements (but not all - which is why
inputs and text areas look different at width: 100%;).
Applying this to all elements is safe and wise:
CSS Box Sizing Property
Property | Description |
---|---|
box-sizing | Defines how the width and height of an element are calculated: should they include padding and borders, or not |