Background Color, paragraph 1:

This paragraph of text has background color #CCCC66 added to it's style.

Padding added, paragraph 2:

This paragraph of text is a copy of paragraph 1 with padding of 10px added to it's style.

Border added, paragraph 3:

This paragraph of text is a copy of paragraph 2 with a border of 2.5 px solid #333333 added to it's style.

Margin added, paragraph 4:

This paragraph of text is a copy of paragraph 3 with a margin of 35px added to it's style.

Size of the Box

To calculate the size of the box, I have a added a width of 400px to the content. I then add the 400px width of the content to the 20px right + left width of the padding, plus the 5px right + left width of the border, plus the 70px right + left width of the margin for a total width of 495px.