How Can I Make a DIV's Border Appear Inside Its Dimensions?

Making Borders Appear Inside DIV Elements

In web design, understanding how elements interact and behave is crucial. One common issue developers encounter is placing borders inside a DIV element while maintaining its desired dimensions.

The default behavior of CSS is to place the border on the outer edge of the element, effectively increasing its width and height. To counter this, the box-sizing property comes into play. By setting box-sizing: border-box, the border is included within the element's width and height specifications, resulting in an accurate representation of the intended dimensions.

Here's an example to illustrate this concept:

div {
    box-sizing: border-box;
    -moz-box-sizing: border-box;
    -webkit-box-sizing: border-box;
    width: 100px;
    height: 100px;
    border: 20px solid #f00;
    background: #00f;
    margin: 10px;
}

div + div {
    border: 10px solid red;
}

In this example, the first DIV has a box-sizing property set to border-box, giving it a width and height of 100px, including the 20px border. By contrast, the second DIV has no box-sizing property defined, resulting in a border that extends beyond the element's specified dimensions.

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