Children inherit traits from their parents—eye color, height, male-pattern baldness, and so on. Sometimes, we inherit traits from more distant ancestors like grandparents or great-grandparents. As you saw in the previous chapter, the metaphor of family-relations is part of the structure of HTML as well. And just like humans, HTML tags can inherit CSS properties from their ancestors.
In a nutshell, inheritance is the process by which CSS properties applied to one tag are passed on to nested tags. For example, a <p> tag is always nested inside of the <body> tag, so properties applied to the <body> tag get inherited by the <p> tag. Say you created a CSS tag style (Section 3.1) for the <body> tag that sets the color property to a dark red. Tags that are descendents of the <body> tag—that is, the ones inside the <body> tag—will inherit that color property. That means that any text in those tags—<h1>, <h2>, <p>, whatever—will appear in that same dark red color.
Inheritance works through multiple generations as well. If a tag like the <em> or <strong> tag appears inside of a <p> tag, then the <em> and the <strong> tags also inherit properties from any style applied to the <body> tag.
Note
As discussed in Chapter 3, any tag inside of another tag is a descendent of that tag. So a <p> tag inside the <body> tag is a descendent of the <body>, while the <body> tag is an ancestor of the <p> tag. Descendents (think kids) inherit properties from ancestors (think parents and grandparents).
Although this sounds a bit confusing, inheritance is a really big time-saver. Imagine if no properties were passed onto nested tags and you had a paragraph that contained other tags like the <em> tag to emphasize text or the <a> tag to add a link. If you created a style that made the paragraph purple, 24px tall, using the Arial font, it would be weird if all the text inside the <em> tag reverted to its regular, "browser-boring" style (see Figure 4-1). You'd then have to create another style to format the <em> tag to match the appearance of the <p> tag. What a drag.
Inheritance doesn't just apply to tag styles. It works with any type of style; so when you apply a class style (see Section 3.1) to a tag, any tags inside that tag inherit properties from the styled tag. Same holds true for ID styles, descendent selectors, and the other types of styles discussed in Chapter 3.
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