CSS 笔记五(Combinators/Pseudo-classes/Pseudo-elements)

时间:2022-11-24 23:11:57

CSS Combinators

Four different combinators in CSS3

  • descendant selector (space)
  • child selector (>)
  • adjacent sibling selector (+)
  • general sibling selector (~)

CSS Pseudo-classes

A pseudo-class is used to define a special state of an element.

  • Style an element when a user mouses over it
  • Style visited and unvisited links differently
 selector:pseudo-class {
property:value;
}

Example

 /* unvisited link */
a:link {
color: #FF0000;
} /* visited link */
a:visited {
color: #00FF00;
} /* mouse over link */
a:hover {
color: #FF00FF;
} /* selected link */
a:active {
color: #0000FF;
}

All CSS Pseudo Classes

Selector Example Example description
:active a:active Selects the active link
:checked input:checked Selects every checked <input> element
:disabled input:disabled Selects every disabled <input> element
:empty p:empty Selects every <p> element that has no children
:enabled input:enabled Selects every enabled <input> element
:first-child p:first-child Selects every <p> elements that is the first child of its parent
:first-of-type p:first-of-type Selects every <p> element that is the first <p> element of its parent
:focus input:focus Selects the <input> element that has focus
:hover a:hover Selects links on mouse over
:in-range input:in-range Selects <input> elements with a value within a specified range
:invalid input:invalid Selects all <input> elements with an invalid value
:lang(language) p:lang(it) Selects every <p> element with a lang attribute value starting with "it"
:last-child p:last-child Selects every <p> elements that is the last child of its parent
:last-of-type p:last-of-type Selects every <p> element that is the last <p> element of its parent
:link a:link Selects all unvisited links
:not(selector) :not(p) Selects every element that is not a <p> element
:nth-child(n) p:nth-child(2) Selects every <p> element that is the second child of its parent
: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
: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
:nth-of-type(n) p:nth-of-type(2) Selects every <p> element that is the second <p> element of its parent
:only-of-type p:only-of-type Selects every <p> element that is the only <p> element of its parent
:only-child p:only-child Selects every <p> element that is the only child of its parent
:optional input:optional Selects <input> elements with no "required" attribute
:out-of-range input:out-of-range Selects <input> elements with a value outside a specified range
:read-only input:read-only Selects <input> elements with a "readonly" attribute specified
:read-write input:read-write Selects <input> elements with no "readonly" attribute
:required input:required Selects <input> elements with a "required" attribute specified
:root root Selects the document's root element
:target #news:target Selects the current active #news element (clicked on a URL containing that anchor name)
:valid input:valid Selects all <input> elements with a valid value
:visited a:visited Selects all visited links

CSS Pseudo-elements

A CSS pseudo-element is used to style specified parts of an element.

  • Style the first letter, or line, of an element
  • Insert content before, or after, the content of an element
 selector::pseudo-element {
property:value;
}

Note: The ::first-line pseudo-element can only be applied to block-level elements.

Example

 p::first-letter {
color: #ff0000;
font-size: xx-large;
} p::first-line {
color: #0000ff;
font-variant: small-caps;
}

All CSS Pseudo Elements

Selector Example Example description
::after p::after Insert content after every <p> element
::before p::before Insert content before every <p> element
::first-letter p::first-letter Selects the first letter of every <p> element
::first-line p::first-line Selects the first line of every <p> element
::selection p::selection Selects the portion of an element that is selected by a user