Margins are relative

BODY { margin-left: 50px }

H2 { margin-left: 50px }

H3 { margin-left: 100px }

Element's margin is relative to its enclosing parent.

On this page, BODY has a left margin of 50 pixels. H2 has a left margin of 50 pixels, but this is added to BODY's left margin for an actual left margin of 100 pixels.