17. What is the box model in CSS and what properties define it?

The box model in CSS defines the structure and how space is allocated around an element. It consists of the following elements:

• Content: The content of the element.
• Padding: The inner space between the content and the element's border.
• Border: The border of the element.
• Margin: The outer space around the element, separating it from other elements.

/* Example of box model */
.element {
    width: 100px; /* Content width */
    height: 100px; /* Content height */
    padding: 10px; /* Padding */
    border: 5px solid black; /* Border */
    margin: 20px; /* Margin */
}