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.

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.

Demonstration of the box model:

div {
  width: 300px;
  border: 15px solid green;
  padding: 50px;
  margin: 20px;
}

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