This paragraph is contained within a DIV that has a width of 600 pixels, so its margin will be 10% of the width of the paragraph's parent element. Given the declared width of 600 pixels, the margin will be 60 pixels on all sides.

This paragraph is contained within a DIV with a width of 300 pixels, so its margin will still be 10% of the width of the paragraph's parent. There will, therefore, be half as much margin on this paragraph as on the first paragraph.