CSS Box Model
All HTML elements can be
considered as boxes.
The CSS Box Model
In CSS, the term "box model"
is used when talking about design and layout.
The CSS box model is
essentially a box that wraps around every HTML element. It consists of:
margins, borders, padding, and the actual content. The image below illustrates
the box model:
Explanation of the
different parts:
- Content - The
content of the box, where text and images appear
- Padding - Clears
an area around the content. The padding is transparent
- Border - A border
that goes around the padding and content
- Margin - Clears
an area outside the border. The margin is transparent
The box model allows us to
add a border around elements, and to define space between elements.
Example
Demonstration
of the box model:
div {
width: 300px;
border: 15px solid green;
padding: 50px;
margin: 20px;
}
Width and Height of an Element
In order to set the width
and height of an element correctly in all browsers, you need to know how the
box model works.
Important: When
you set the width and height properties of an element with CSS, you just set
the width and height of the content area. To calculate the full
size of an element, you must also add padding, borders and margins.
Example
This
<div> element will have a total width of 350px:
div {
width: 320px;
padding: 10px;
border: 5px solid gray;
margin: 0;
}
Here is the calculation:
320px (width)
+ 20px (left + right padding)
+ 10px (left + right border)
+ 0px (left + right margin)
= 350px
The total width of an
element should be calculated like this:
Total element width = width
+ left padding + right padding + left border + right border + left margin +
right margin
The total height of an
element should be calculated like this:
Total element height =
height + top padding + bottom padding + top border + bottom border + top margin
+ bottom margin
