| .class | .intro | Selects all elements with class=”intro” | 1 |
| #id | #firstname | Selects the element with id=”firstname” | 1 |
| * | * | Selects all elements | 2 |
| element | p | Selects all <p> elements | 1 |
| element,element | div, p | Selects all <div> elements and all <p> elements | 1 |
| element element | div p | Selects all <p> elements inside <div> elements | 1 |
| element>element | div > p | Selects all <p> elements where the parent is a <div> element | 2 |
| element+element | div + p | Selects all <p> elements that are placed immediately after <div> elements | 2 |
| element1~element2 | p ~ ul | Selects every <ul> element that are preceded by a <p> element | 3 |
| [attribute] | [target] | Selects all elements with a target attribute | 2 |
| [attribute=value] | [target=_blank] | Selects all elements with target=”_blank” | 2 |
| [attribute~=value] | [title~=flower] | Selects all elements with a title attribute containing the word “flower” | 2 |
| [attribute|=value] | [lang|=en] | Selects all elements with a lang attribute value starting with “en” | 2 |
| [attribute^=value] | a[href^=”https”] | Selects every <a> element whose href attribute value begins with “https” | 3 |
| [attribute$=value] | a[href$=”.pdf”] | Selects every <a> element whose href attribute value ends with “.pdf” | 3 |
| [attribute*=value] | a[href*=”w3schools”] | Selects every <a> element whose href attribute value contains the substring “w3schools” | 3 |
| :active | a:active | Selects the active link | 1 |
| ::after | p::after | Insert content after every <p> element | 2 |
| ::before | p::before | Insert content before the content of every <p> element | 2 |
| :checked | input:checked | Selects every checked <input> element | 3 |
| :disabled | input:disabled | Selects every disabled <input> element | 3 |
| :empty | p:empty | Selects every <p> element that has no children (including text nodes) | 3 |
| :enabled | input:enabled | Selects every enabled <input> element | 3 |
| :first-child | p:first-child | Selects every <p> element that is the first child of its parent | 2 |
| ::first-letter | p::first-letter | Selects the first letter of every <p> element | 1 |
| ::first-line | p::first-line | Selects the first line of every <p> element | 1 |
| :first-of-type | p:first-of-type | Selects every <p> element that is the first <p> element of its parent | 3 |
| :focus | input:focus | Selects the input element which has focus | 2 |
| :hover | a:hover | Selects links on mouse over | 1 |
| :in-range | input:in-range | Selects input elements with a value within a specified range | 3 |
| :invalid | input:invalid | Selects all input elemets with an invalid value | 3 |
| :lang(language) | p:lang(it) | Selects every <p> element with a lang attribute equal to “it” (Italian) | 2 |
| :last-child | p:last-child | Selects every <p> element that is the last child of its parent | 3 |
| :last-of-type | p:last-of-type | Selects every <p> element that is the last <p> element of its parent | 3 |
| :link | a:link | Selects all unvisited links | 1 |
| :not(selector) | :not(p) | Selects every element that is not a <p> element | 3 |
| :nth-child(n) | p:nth-child(2) | Selects every <p> element that is the second child of its parent | 3 |
| :nth-last-child(n) | p:nth-last-child(2) | Selects every <p> element that is the second child of its parent, counting from the last child | 3 |
| :nth-last-of-type(n) | p:nth-last-of-type(2) | Selects every <p> element that is the second <p> element of its parent, counting from the last child | 3 |
| :nth-of-type(n) | p:nth-of-type(2) | Selects every <p> element that is the second <p> element of its parent | 3 |
| :only-of-type | p:only-of-type | Selects every <p> element that is the only <p> element of its parent | 3 |
| :only-child | p:only-child | Selects every <p> element that is the only child of its parent | 3 |
| :optional | input:optional | Selects input elements with no “required” attribute | 3 |
| :out-of-range | input:out-of-range | Selects input elements with a value outside a specified range | 3 |
| :read-only | input:read-only | Selects input elements with the “readonly” attribute specified | 3 |
| :read-write | input:read-write | Selects input elements with the “readonly” attribute NOT specified | 3 |
| :required | input:required | Selects input elements with the “required” attribute specified | 3 |
| :root | :root | Selects the document’s root element | 3 |
| ::selection | ::selection | Selects the portion of an element that is selected by a user | |
| :target | #news:target | Selects the current active #news element (clicked on a URL containing that anchor name) | 3 |
| :valid | input:valid | Selects all input elements with a valid value | 3 |
| :visited | a:visited | Selects all visited links | 1 |
from http://www.w3schools.com/cssref/css_selectors.asp
Bello da leggere anche: http://www.bedev.it/css-3/10-selettori-css-da-non-dimenticare/