What is the CSS box model?

The CSS box model describes how HTML elements are surrounded by margins, border, padding; all containing the content.

What is the difference between margin and padding?

Margin is the spacing between elements. Padding is the space inside of the element surrounding the content.

How is the total height and width of an HTML element determined?

The total height and width of an HTML element is determined by adding the height and width of the element to the margin and padding on all sides.

Explain this CSS property: padding: 25px 50px;

There will be 25 pixels of space on the top and bottom, and 50 pixels on the left and right of the element between the outer edge of the box and the content within.