CSS works by:
The result is a render tree that is presented for display or committed to various page-based formats.
Styles cascade:
For example, if you set the font family to Arial
on the body
element, all its children will inherit that font family.
That is, unless another rule changes the property.
The properties cascade
through the document structure.
⇓ a selector body { font-family: "Palatino Linotype", "Book Antiqua", Palatino, serif; line-height: 1.25em; color: #252c58 } ⇑ a block (curly bracketed content) ⇓ selectors can be separated by commas for grouping h1, h2, h3, h4, h5, figcaption, caption { font-family: Helvetica, Arial, sans-serif; } h2 { font-size: 1.25em; ⇑ a property and value; ends with a semicolon } div.slide h1 + * { margin-top: 2em; } div.slide h1 + img { ⇐ there are rules for which selector is more specific margin-top: 1em; }
selector { property-1 : value ; property-2 : value ; ... } ... selector-1, selector-2, ... { property-1 : value ; property-2 : value ; ... }
Values can be:
1
, 2
, ...12.5
, 1.25
10%
10cm
, 1.25em
, 12pt
url(http://www.example.com/background.png)
or url("http://www.example.com/background.png")
"The quick brown fox"
or 'The quick brown fox'
#ff0000
or rgb(255,0,0)
inline
or left
Pattern | Meaning | Described in section | First defined in CSS level |
---|---|---|---|
* | any element | Universal selector | 2 |
E | an element of type E | Type selector | 1 |
E[foo] | an E element with a "foo" attribute | Attribute selectors | 2 |
E[foo="bar"] | an E element whose "foo" attribute value is exactly equal to "bar" | Attribute selectors | 2 |
E[foo~="bar"] | an E element whose "foo" attribute value is a list of whitespace-separated values, one of which is exactly equal to "bar" | Attribute selectors | 2 |
E[foo^="bar"] | an E element whose "foo" attribute value begins exactly with the string "bar" | Attribute selectors | 3 |
E[foo$="bar"] | an E element whose "foo" attribute value ends exactly with the string "bar" | Attribute selectors | 3 |
E[foo*="bar"] | an E element whose "foo" attribute value contains the substring "bar" | Attribute selectors | 3 |
Pattern | Meaning | Described in section | First defined in CSS level |
---|---|---|---|
E[foo|="en"] | an E element whose "foo" attribute has a hyphen-separated list of values beginning (from the left) with "en" | Attribute selectors | 2 |
E:root | an E element, root of the document | Structural pseudo-classes | 3 |
E:nth-child(n) | an E element, the n-th child of its parent | Structural pseudo-classes | 3 |
E:nth-last-child(n) | an E element, the n-th child of its parent, counting from the last one | Structural pseudo-classes | 3 |
E:nth-of-type(n) | an E element, the n-th sibling of its type | Structural pseudo-classes | 3 |
E:nth-last-of-type(n) | an E element, the n-th sibling of its type, counting from the last one | Structural pseudo-classes | 3 |
E:first-child | an E element, first child of its parent | Structural pseudo-classes | 2 |
E:last-child | an E element, last child of its parent | Structural pseudo-classes | 3 |
Pattern | Meaning | Described in section | First defined in CSS level |
---|---|---|---|
E:first-of-type | an E element, first sibling of its type | Structural pseudo-classes | 3 |
E:last-of-type | an E element, last sibling of its type | Structural pseudo-classes | 3 |
E:only-child | an E element, only child of its parent | Structural pseudo-classes | 3 |
E:only-of-type | an E element, only sibling of its type | Structural pseudo-classes | 3 |
E:empty | an E element that has no children (including text nodes) | Structural pseudo-classes | 3 |
E:link E:visited |
an E element being the source anchor of a hyperlink of which the target is not yet visited (:link) or already visited (:visited) | The link pseudo-classes | 1 |
E:active E:hover E:focus |
an E element during certain user actions | The user action pseudo-classes | 1 and 2 |
Pattern | Meaning | Described in section | First defined in CSS level |
---|---|---|---|
E:target | an E element being the target of the referring URI | The target pseudo-class | 3 |
E:lang(fr) | an element of type E in language "fr" (the document language specifies how language is determined) | The :lang() pseudo-class | 2 |
E:enabled E:disabled |
a user interface element E which is enabled or disabled | The UI element states pseudo-classes | 3 |
E:checked | a user interface element E which is checked (for instance a radio-button or checkbox) | The UI element states pseudo-classes | 3 |
E::first-line | the first formatted line of an E element | The ::first-line pseudo-element | 1 |
E::first-letter | the first formatted letter of an E element | The ::first-letter pseudo-element | 1 |
E::before | generated content before an E element | The ::before pseudo-element | 2 |
E::after | generated content after an E element | The ::after pseudo-element | 2 |
Pattern | Meaning | Described in section | First defined in CSS level |
---|---|---|---|
E.warning | an E element whose class is "warning" (the document language specifies how class is determined). | Class selectors | 1 |
E#myid | an E element with ID equal to "myid". | ID selectors | 1 |
E:not(s) | an E element that does not match simple selector s | Negation pseudo-class | 3 |
E F | an F element descendant of an E element | Descendant combinator | 1 |
E > F | an F element child of an E element | Child combinator | 2 |
E + F | an F element immediately preceded by an E element | Adjacent sibling combinator | 2 |
E ~ F | an F element preceded by an E element | General sibling combinator | 3 |
A selector's specificity is calculated as follows:
* /* a=0 b=0 c=0 -> specificity = 0 */ LI /* a=0 b=0 c=1 -> specificity = 1 */ UL LI /* a=0 b=0 c=2 -> specificity = 2 */ UL OL+LI /* a=0 b=0 c=3 -> specificity = 3 */ H1 + *[REL=up] /* a=0 b=1 c=1 -> specificity = 11 */ UL OL LI.red /* a=0 b=1 c=3 -> specificity = 13 */ LI.red.level /* a=0 b=2 c=1 -> specificity = 21 */ #x34y /* a=1 b=0 c=0 -> specificity = 100 */ #s12:not(FOO) /* a=1 b=0 c=1 -> specificity = 101 */
Too many to enumerate, but here are some resources:
There is also the old school method of a book on CSS.