To place the border inside of div and not on its edge with CSS. we set the box-sizing property.
For instance, we write
<div>Hello!</div>
<div>Hello!</div>
to add divs.
Then we write
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;
}
to set box-sizing to border-box to put the border inside the divs.
We add the border with border: 20px solid #f00;.
