In an embedded or linked style sheet, a selector is the markup you are altering the appearance of. There are several different selection methods, the simplest of which are shown below:

CSS Selector Syntax, CSS Levels 1 and 2

Name	Example	Use
Universal or “wildcard” selector	* { outline: none; }	For selecting every element in a document (or site-wide, if used in a linked style sheet). Used for “CSS resets”: setting all elements to the same appearance properties.
Single selector	p { color: green; }	To select a single tag.
Grouped selectors	h1, h2, h3 { color: red; }	To have multiple elements share the same style rule(s).
Descendant selector	ul li { font-weight: bold; }	Applies the style declaration that applies only to the last element if it is a descendant of the selector sequence. For the example shown, li elements will be bold, but only if they are in the context of (i.e. descend from) a ul element. (li elements in ordered lists will be unaffected)
Sibling selector	h2 ~ p { font-color: red; }	Selects all matching elements that follow at the level of the leading element
Adjacent selector	h2 + p { font-style: italic; }	Selects the element if it comes immediately after the one before it. In the example shown, the first paragraph immediately after an h2 element will be italicized. Other paragraphs outside of this context will be unaffected.
id selector	ul#nav { background: blue; }	Selects elements that have an id that matches the word following the pound sign. Note that this id must be unique to the page. (The same id can be used on multiple pages, but only once per page).
Class selector	p.special { color: red; }	Selects elements that have a class attribute with a value matching the word following the period in the selector. Classes may be used multiple times on a page, but should not be the majority of content associated with that element.
Attribute value selector	input[type=”text”]	Applies only to tags in which an attribute has a particular value.