You might have noticed that styles can be specified at four levels:
tag selector
class selector
id selector
an individual element's style attribute
Styles lower on the list override styles at the top of the list. For example, if you
specify a color with a tag selector, it will be overridden by the color within a
class selector. This is what is referred to as the cascade.
Compare the results for the following examples with the source code for this page:
Example 1: the text for this bullet is green because it only has styles defined by a
single class selector
Example 2: the text for this bullet is red because the id selector overrides
the color specified in the class selector
Example 3: the text for this bullet is blue because the .blue class selector
comes after the .green class selector in the <style> tag