Some common styles set by tags:

Normal Bold Italic Underlined Red Bigger Times Normal

Some common styles set by span. Should look the same as above:

Normal Bold Italic Underlined Red Bigger Times Normal

Font sizes are defined to be relative but in reality all browsers use fixed sizes. We go with the main stream. Here the regular example

Normal 1 2 3 4 5 6 7

The following is inside a <div style="font-size: 16pt">:

Normal smaller larger -4 -3 -2 -1 +2 +3 +4 +5

The following is inside an <h2>:

Normal smaller larger -4 -3 -2 -1 +2 +3 +4 +5