What are margin-top and margin-bottom properties?

The "margin-top" property specifies the space above and the "margin-bottom" specifies the space below. To set these for all h2 headings you can write:

h2 { margin-top: 8em; margin-bottom: 3em; }

The em is a very useful unit as it scales with the size of the font. One em is the height of the font. By using em's you can preserve the general look of the Web page independently of the font size. This is much safer than alternatives such as pixels or points, which can cause problems for users who need large fonts to read the text.

To specify the space above a particular heading, you should create a named style for the heading. You do this with the class attribute in the markup, e.g.

<h2 class="subsection">Getting started</h2>

The style rule is then written as:

h2.subsection {margin-top: 8em; margin-bottom: 3em ;}

The rule starts with the tag name, a dot and then the value of the class attribute. Be careful to avoid placing a space before or after the dot. If you do the rule won't work. There are other ways to set the styles for a particular element but the class attribute is the most flexible.

When a heading is followed by a paragraph, the value for margin-bottom for the heading isn't added to the value for margin-top for the paragraph. Instead, the maximum of the two values is used for the spacing between the heading and paragraph. This subtlety applies to margin-top and margin-bottom regardless of which tags are involved.

Do NOT leave spaces between the property value and the units! If you use "margin-left: 20 px" instead of "margin-left: 20px" it will only work properly in IE6 but it will not work in Mozilla or Netscape.

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