CSS Box Model
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see GIF
All HTML elements can be considered as boxes. In CSS, the term "box model" is used when talking about design and layout.
The box model allows us to place a border around elements and space elements in relation to other elements.
The CSS box model is essentially a box that wraps around HTML elements, and it consists of: margins, borders, padding, and the actual content.
Margin - Clears an area around the border. The margin does not have a background color, it is completely transparent
Border - A border that goes around the padding and content. The border is affected by the background color of the box
Padding - Clears an area around the content. The padding is affected by the background color of the box
Content - The content of the box, where text and images appear
In order to set the width and height of an element correctly in all browsers, you need to know how the box model works.
Width and Height of an Element
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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 the padding, borders and margins.
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
width:250px;
padding:10px;
border:5px solid gray;
margin:10px;
250px (width)
+ 20px (left + right padding)
+ 10px (left + right border)
+ 20px (left + right margin)
= 300px
Browsers Compatibility Issue
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IE8 and earlier versions of IE, included padding and border in the width property.
To fix this problem, add a for HTML 5 to the HTML page.