Related
if I add a css class to my div, it will be overwritten with v-slot-tradeMatrixLayout. How can I specify this class specifically in my CSS file so that only this is called. The tradeMatrixLayout is given to a VerticalLayout.
This will be examined in chrome
<div class="v-slot v-slot-tradeMatrixLayout">
And this is my CSS file
.tradeMatrixLayout{
margin-left: 15px !important;
}
How can the div call my specifically written class?
The class attribute can receive multiple CSS classes by using their name and separated by a space, as seen here. For your case you can add it like:
<div class="v-slot tradeMatrixLayout">
In this example, you are adding 2 classes: v-slot and tradeMatrixLayout.
if v-slot is overwritting whatever you are trying to set with tradeMatrixLayout, then it means that you have to play with Specificity. In summary, some rules have more importance than others, even if you use !important (imagine you have 3 classes that use !important, which one should be used?). The higher the specificity, the more important is the rule.
The following list of selector types increases by specificity:
Type selectors (e.g., h1) and pseudo-elements (e.g., ::before).
Class selectors (e.g., .example), attributes selectors (e.g.,
[type="radio"]) and pseudo-classes (e.g., :hover).
ID selectors (e.g., > #example).
if you want it to have more specificity, either change your CSS to:
div.tradeMatrixLayout{
margin-left: 15px;
}
of add it using an id:
<div id="myDiv" class="v-slot tradeMatrixLayout">
div#myDiv.tradeMatrixLayout{
margin-left: 15px;
}
You can also use javascript to add the class by manipulating the DOM.
function myFunction() {
var el = document.getElementsByClassName("v-slot");
el.classList.add("tradeMatrixLayout");
}
it should be end with your class
[class$='tradeMatrixLayout']{
color: red;
margin-left: 15px !important;
}
Just try above code it will work for you
The .class selector selects elements with a specific class attribute.
To select elements with a specific class, write a period (.) character, followed by the name of the class.
You can also specify that only specific HTML elements should be affected by a class. To do this, start with the element name, then write the period (.) character, followed by the name of the class
I don't fully understand what you clearly want though? What you have seems okay?
v-slot v-slot-gewerkeMatrixLayout
This is referencing to these 2 classes, It cannot use the same elements from both as it will be overwritten. But if you have 2 different instructions it should work
You could just specify the class your in your CSS like this
.v-slot-tradeMatrixLayout {
margin-left: 15px !important;
}
Just add another CSS with that CSS class (v-slot)
Like:
.v-slot{
margin-right:5px;
}
.v-slot.tradeMatrixLayout{
margin-left:50px
}
And your html will look like
<div class="v-slot"></div>
<div class="v-slot tradeMatrixLayout"></div>
.v-slot{
border: 3px solid blue;
height: 50px;
width: 50px;
margin-left: 5px;
}
.v-slot.tradeMatrixLayout{
margin-left:50px
}
<div class="v-slot"></div>
<div class="v-slot tradeMatrixLayout"></div>
I'm new to CSS and want to learn how to make webpages. While learning on Codecademy there was a lesson for classes and Ids which got me confused.
How should the classes be setup and does it make a difference if it's like this
.content h1 {
}
or
h1 .content {
}
Firstly, the spaces in between the CSS selectors .content and h1 matter, meaning, if you are trying to make a CSS rule specifically for h1 elements with a class of content, then the rule needs to be formatted as h1.content.
Secondly, a CSS rule with a space in between selectors (e.g. div .bold) is a combinator known as a descendant selector, and in the example div .bold { font-weight: bold; }, it would mean that any elements with class bold descending from any div element would have a bold font weight style applied.
element.classname mean you are targeting the tag having a class as classname.
element .classname or .classname element mean you are targeting the html element having class classname which is a child/descendent of tag.
Things like a:link or div::after...
Information on the difference seems scarce.
The CSS 3 selector recommendation is pretty clear about both, but I'll try to show the differences anyway.
Pseudo-classes
Official description
The pseudo-class concept is introduced to permit selection based on information that lies outside of the document tree or that cannot be expressed using the other simple selectors.
A pseudo-class always consists of a "colon" (:) followed by the name of the pseudo-class and optionally by a value between parentheses.
Pseudo-classes are allowed in all sequences of simple selectors contained in a selector. Pseudo-classes are allowed anywhere in sequences of simple selectors, after the leading type selector or universal selector (possibly omitted). Pseudo-class names are case-insensitive. Some pseudo-classes are mutually exclusive, while others can be applied simultaneously to the same element. Pseudo-classes may be dynamic, in the sense that an element may acquire or lose a pseudo-class while a user interacts with the document.
Source
What does this mean?
The important nature of pseudo-classes is stated in the very first sentence: "the pseudo-class concept [...] permit selection". It enables the author of an stylesheet to differ between elements based on information that "lies outside of the document tree", for example the current status of a link (:active,:visited). Those aren't saved anywhere in the DOM, and there exists no DOM interface to access these options.
On the other hand, :target could be accessed via DOM manipulation (you could use window.location.hash in order to find the object with JavaScript), but this "cannot be expressed using the other simple selectors".
So basically a pseudo-class will refine the set of selected elements as any other simple selector in a sequence of simple selectors. Note that all simple selectors in a sequence of simple selectors will be evaluated at the same time. For a complete list of pseudo-class check the CSS3 selector recommendation.
Example
The following example will color all even rows gray (#ccc), all uneven rows which aren't dividable by 5 white and every other row magenta.
table tr:nth-child(2n) td{
background-color: #ccc;
}
table tr:nth-child(2n+1) td{
background-color: #fff;
}
table tr:nth-child(2n+1):nth-child(5n) td{
background-color: #f0f;
}
Pseudo-elements
Official description
Pseudo-elements create abstractions about the document tree beyond those specified by the document language. For instance, document languages do not offer mechanisms to access the first letter or first line of an element's content. Pseudo-elements allow authors to refer to this otherwise inaccessible information. Pseudo-elements may also provide authors a way to refer to content that does not exist in the source document (e.g., the ::before and ::after pseudo-elements give access to generated content).
A pseudo-element is made of two colons (::) followed by the name of the pseudo-element.
This :: notation is introduced by the current document in order to establish a discrimination between pseudo-classes and pseudo-elements. For compatibility with existing style sheets, user agents must also accept the previous one-colon notation for pseudo-elements introduced in CSS levels 1 and 2 (namely, :first-line, :first-letter, :before and :after). This compatibility is not allowed for the new pseudo-elements introduced in this specification.
Only one pseudo-element may appear per selector, and if present it must appear after the sequence of simple selectors that represents the subjects of the selector.
Note: A future version of this specification may allow multiple pseudo-elements per selector.
Source
What does this mean?
The most important part here is that "pseudo-elements allow authors to refer to [..] otherwise inaccessible information" and that they "may also provide authors a way to refer to content that does not exist in the source document (e.g., the ::before and ::after pseudo-elements give access to generated content).". The biggest difference is that they actually create a new virtual element on which rules and even pseudo-class selectors can be applied to. They don't filter elements, they basically filter content (::first-line,::first-letter) and wrap it in a virtual container, which the author can style however he want (well, almost).
For example the ::first-line pseudo-element cannot be reconstructed with JavaScript, as it heavily depends on the current used font, the fonts size, the elements width, floating elements (and probably the time of the day). Well, that's not entirely true: one could still calculate all those values and extract the first line, however doing so is a very cumbersome activity.
I guess the biggest difference is that "only one pseudo-element may appear per selector". The note says that this could be subject to change, but as of 2012 I don't believe we see any different behavior in the future (it's still in CSS4).
Example
The following example will add a language-tag to every quote on a given page using the pseudo-class :lang and the pseudo-element ::after:
q:lang(de)::after{
content: " (German) ";
}
q:lang(en)::after{
content: " (English) ";
}
q:lang(fr)::after{
content: " (French) ";
}
q:not(:lang(fr)):not(:lang(de)):not(:lang(en))::after{
content: " (Unrecognized language) ";
}
TL;DR
Pseudo-classes act as simple selectors in a sequence of selectors and thereby classify elements on non-presentational characteristics, pseudo-elements create new virtual elements.
References
W3C
Selectors Level 3
4. Selector syntax
6.6 Pseudo-classes
7. Pseudo-elements
CSS 2.1 Specification (outdated but still informative)
5.2 Selector syntax:
A simple selector is either a type selector or universal selector followed immediately by zero or more attribute selectors, ID selectors, or pseudo-classes, in any order. The simple selector matches if all of its components match.
5.10 Pseudo-elements and pseudo-classes
A pseudo-class filters existing elements.
a:link means all <a>s that are :link.
A pseudo-element is a new fake element.
div::after means non-existing elements after <div>s.
::selection is another example of a pseudo-element.
It doesn't mean all elements that are selected; it means the range of content that is selected, which may span portions of multiple elements.
Short description that helped me to understand the difference:
Pseudo-classes describe a special state.
Pseudo-elements match virtual elements.
From the Sitepoint docs:
A pseudo-class is similar to a class in HTML, but it’s not specified explicitly in the markup. Some pseudo-classes are dynamic—they’re applied as a result of user interaction with the document. - http://reference.sitepoint.com/css/pseudoclasses. These would be things like :hover, :active, :visited.
Pseudo-elements match virtual elements that don’t exist explicitly in the document tree. Pseudo-elements can be dynamic, inasmuch as the virtual elements they represent can change, for example, when the width of the browser window is altered. They can also represent content that’s generated by CSS rules. - http://reference.sitepoint.com/css/pseudoelements. These would be things like ::before, ::after, ::first-letter.
Below is the simple answer:
We use pseudo-class when we need to apply css based on the state of an element. Such as:
Apply css on hover of anchor element (:hover)
Apply css when gets focus on an html element (:focus). etc.
We use pseudo-element when we need to apply css to the specific parts of an elements or a newly inserted content. Such as:
Apply the css to first letter or first line of an element (::first-letter)
Insert content before, or after, the content of an element (::before, ::after)
Below is the example of both:
<html>
<head>
<style>
p::first-letter { /* pseudo-element */
color: #ff0000;
}
a:hover { /* pseudo-class */
color: red;
}
</style>
</head>
<body>
<a href="#" >This is a link</a>
<p>This is a paragraph.</p>
</body>
</html>
A conceptual answer:
A pseudo-element refers to things that are part of the document, but you just don't know it yet. For example the first letter. Before you only had text. Now you have a first letter that you can target. It is a new concept, but was always part of the document. This also includes things like ::before; while there isn't actual content there, the concept of something before something else was always there -- now you are specifying it.
A pseudo-class is state of something in the DOM. Just like a class is a tag you associate with an element, a pseudo-class is a class that gets associated by the browser or DOM or whatever, usually as a response to a change in state. When a user visits a link -- that link can take on the state of 'visited'. You can imagine the browser applying the class 'visited' to the Anchor element. :visited would then be how you select for that pseudo-class.
Pseudo-Class
A pseudo-class is way of selecting certain parts of a HTML document, based in principle not on the HTML document tree itself and its elements or on characteristics like name, attributes or contents, but on other phantom conditions like language encoding or the dynamic state of an element.
The original pseudo-class defined dynamic states of an element that are entered and exited over time, or through user intervention. CSS2 expanded on this concept to include virtual conceptual document components or inferred portions of the document tree e.g. first-child. Pseudo-classes operate as if phantom classes were added to various elements.
RESTRICTIONS: Unlike pseudo-elements, pseudo-classes can appear anywhere in selector chain.
Example pseudo-class code:
a:link /* This selects any "a" element whose target has not been visited.*/
{
padding : 4px;
text-decoration : none;
width : 10%;
color : #000000; /* black text color */
background-color : #99FF99; /* set to a pastel green */
border-top : 2px solid #ccffcc; /* highlight color */
border-left : 2px solid #ccffcc; /* highlight color */
border-bottom : 2px solid #003300; /* shadow color */
border-right : 2px solid #003300; /* shadow color */
}
a:visited /* This selects any "a" element whose target has been visited.*/
{ padding : 4px;
text-decoration : none;
color : #000000; /* black text color */
background-color : #ccccff; /* set to a lavender */
border-top : 2px solid #ffffff; /* highlight color */
border-left : 2px solid #ffffff; /* highlight color */
border-bottom : 2px solid #333366; /* shadow color *
border-right : 2px solid #333366; /* shadow color */
}
a:hover /* This selects any "a" element which is in a hover state. This is a state during pointer movement within the rendering region of an element. The user designates an element but does not activate it. */
{
color : #000000; /* black text color */
background-color : #99cc99; /* desaturated color */
border-top : 2px solid #003300; /* shadow color */
border-left : 2px solid #003300; /* shadow color */
border-bottom : 2px solid #ccffcc; /* highlight color */
border-right : 2px solid #ccffcc; /* highlight color */
}
a:focus /* This selects any "a" element which currently has focus. Focus is a state during which an element accepts keyboard input or other forms of text input. */
{
padding : 4px;
text-decoration : none;
width : 10%;
color : #000000; /* black text color */
background-color : #ffff99; /* set to a pastel yellow */
border-top : 2px solid #ffffcc; /* highlight color */
border-left : 2px solid #ffffcc; /* highlight color */
border-bottom : 2px solid #666633; /* shadow color */
border-right : 2px solid #666633; /* shadow color */
}
a:active /* This selects any "a" element which is in a state of activation. Active is a state during pointer activation (eg: press and release of a mouse) within the rendering region of an element.*/
{
padding : 4px;
text-decoration : none;
width : 10%;
color : #000000; /* black text color */
background-color : #ff99ff; /* set to a pink */
border-top : 2px solid #ffccff; /* highlight color */
border-left : 2px solid #ffccff; /* highlight color */
border-bottom : 2px solid #663366; /* shadow color */
border-right : 2px solid #663366; /* shadow color */
}
A page that demonstrates a rendering of the above pseudo-class code
Pseudo-elements
PSEUDO-ELEMENTS are used to address sub-parts of elements. They allow you to set style on a part of an element's content beyond what is specified in the documents. In other words they allow logical elements to be defined which are not actually in the document element tree. Logical elements allow implied semantic structure to be addressed in CSS selectors.
RESTRICTIONS: Pseudo-elements may only be applied to external and document-level contexts - not to in-line styles. Pseudo-elements are restricted in where they can appear in a rule. They may only appear at the end of a selector chain (after the subject of the selector). They should come after any class or ID names found in the selector. Only one pseudo-element can be specified per selector. To address multiple pseudo-elements on a single element structure, multiple style selector/declaration statements must be made.
Pseudo-elements can be used for common typographic effects such as initial caps and drop caps. They can also address generated content that is not in the source document (with the "before" and "after") An example style sheet of some pseudo-elements with properties and values added follows.
/* The following rule selects the first letter of a heading 1 and sets the font to 2em, cursive, with a green background. First-letter selects the first rendered letter/character for a block-level element. */
h1:first-letter {
font-size : 2em;
font-family : "Lucida Handwriting", "Lucida Sans", "Lucida Console", cursive;
background-color : #ccffcc;
}
/* The following rule selects the first displayed line in a paragraph and makes it bold. First-line selects the first rendered line on the output device of a block-level element. */
p:first-line {
font-weight : bold;
}
/* The following rule selects any content placed before a blockquote and inserts the phrase "Quote of the day:" in bold small caps with a green background. */
blockquote:before {
content : "Quote of the day:";
background-color : #ccffcc;
font-weight : bold;
font-variant : small-caps;
}
/* The following rule selects any content placed before a "q" element and inserts the smart open quote. */
q:before {
content : open-quote;
}
/* The following rule selects any content placed after a "q" element and inserts the smart close quote. */
q:after{
content : close-quote;
}
Sources:Link
In brief, from Pseudo-classes on MDN:
A CSS pseudo-class is a keyword added to a selector that specifies
a special state of the selected element(s). For example, :hover
can be used to apply a style when the user hovers over a button.
div:hover {
background-color: #F89B4D;
}
And, from Pseudo-elements on MDN:
A CSS pseudo-element is a keyword added to a selector that lets you
style a specific part of the selected element(s). For example,
::first-line can be used to style the first line of a paragraph.
/* The first line of every <p> element. */
p::first-line {
color: blue;
text-transform: uppercase;
}
Can someone explain the difference for these two CSS selectors?
.work-container . h3 {
font-size: 14px;
margin-top: 0px;
font-weight: 600;
height: 27px;
}
What is the extra dot in the upper definition?
.work-container h3 {
font-size: 14px;
margin-top: 0px;
font-weight: 600;
height: 27px;
}
Cases
Selector start with dot
.class_name signifies class name
Two dotted selector separated by space
.outside .inside
means element with .inside class descended from an element with class .outside
Two dotted selector without separation
.name1.name2
means element that has both class name1 and name2
eg: class="name1 name2"
Related questions:
What does a space mean in a CSS selector? i.e. What is the difference between .classA.classB and .classA .classB?
What's the difference between CSS classes .foo.bar (without space) and .foo .bar (with space)
A . prefix usually represents a class selector, but if it's immediately followed by whitespace then it's a syntax error.
If I were to hazard a guess, then it's likely the author meant to say .work-container > h3, but missed the Shift key just as he was about to type the > character (the child combinator).
Your second selector, .work-container h3, simply means any h3 that's contained within an element with a class called work-container.
. in CSS means it is a class and it can be applied to many elements.
# in CSS means it is an ID and it can be applied to one element per page.
Without the either, it is a tag, targets all the elements with the tag name.
In your syntax, .work-container . h3 is actually error. The . should have been either , or as BoltClock said, >, which says the direct descendant operator in CSS.
. says its class
# means its an id
and if there is nothing but the selector, then it is a tag
. in CSS means it is a class & it can be applied to many elements with use space between classes
For example:
<h3 class="class1 class2 class2">Heading</h3>
# in CSS means it is an ID and it can be applied to one element per page.
For example
<h3 id="idname1">Heading</h3>
Things like a:link or div::after...
Information on the difference seems scarce.
The CSS 3 selector recommendation is pretty clear about both, but I'll try to show the differences anyway.
Pseudo-classes
Official description
The pseudo-class concept is introduced to permit selection based on information that lies outside of the document tree or that cannot be expressed using the other simple selectors.
A pseudo-class always consists of a "colon" (:) followed by the name of the pseudo-class and optionally by a value between parentheses.
Pseudo-classes are allowed in all sequences of simple selectors contained in a selector. Pseudo-classes are allowed anywhere in sequences of simple selectors, after the leading type selector or universal selector (possibly omitted). Pseudo-class names are case-insensitive. Some pseudo-classes are mutually exclusive, while others can be applied simultaneously to the same element. Pseudo-classes may be dynamic, in the sense that an element may acquire or lose a pseudo-class while a user interacts with the document.
Source
What does this mean?
The important nature of pseudo-classes is stated in the very first sentence: "the pseudo-class concept [...] permit selection". It enables the author of an stylesheet to differ between elements based on information that "lies outside of the document tree", for example the current status of a link (:active,:visited). Those aren't saved anywhere in the DOM, and there exists no DOM interface to access these options.
On the other hand, :target could be accessed via DOM manipulation (you could use window.location.hash in order to find the object with JavaScript), but this "cannot be expressed using the other simple selectors".
So basically a pseudo-class will refine the set of selected elements as any other simple selector in a sequence of simple selectors. Note that all simple selectors in a sequence of simple selectors will be evaluated at the same time. For a complete list of pseudo-class check the CSS3 selector recommendation.
Example
The following example will color all even rows gray (#ccc), all uneven rows which aren't dividable by 5 white and every other row magenta.
table tr:nth-child(2n) td{
background-color: #ccc;
}
table tr:nth-child(2n+1) td{
background-color: #fff;
}
table tr:nth-child(2n+1):nth-child(5n) td{
background-color: #f0f;
}
Pseudo-elements
Official description
Pseudo-elements create abstractions about the document tree beyond those specified by the document language. For instance, document languages do not offer mechanisms to access the first letter or first line of an element's content. Pseudo-elements allow authors to refer to this otherwise inaccessible information. Pseudo-elements may also provide authors a way to refer to content that does not exist in the source document (e.g., the ::before and ::after pseudo-elements give access to generated content).
A pseudo-element is made of two colons (::) followed by the name of the pseudo-element.
This :: notation is introduced by the current document in order to establish a discrimination between pseudo-classes and pseudo-elements. For compatibility with existing style sheets, user agents must also accept the previous one-colon notation for pseudo-elements introduced in CSS levels 1 and 2 (namely, :first-line, :first-letter, :before and :after). This compatibility is not allowed for the new pseudo-elements introduced in this specification.
Only one pseudo-element may appear per selector, and if present it must appear after the sequence of simple selectors that represents the subjects of the selector.
Note: A future version of this specification may allow multiple pseudo-elements per selector.
Source
What does this mean?
The most important part here is that "pseudo-elements allow authors to refer to [..] otherwise inaccessible information" and that they "may also provide authors a way to refer to content that does not exist in the source document (e.g., the ::before and ::after pseudo-elements give access to generated content).". The biggest difference is that they actually create a new virtual element on which rules and even pseudo-class selectors can be applied to. They don't filter elements, they basically filter content (::first-line,::first-letter) and wrap it in a virtual container, which the author can style however he want (well, almost).
For example the ::first-line pseudo-element cannot be reconstructed with JavaScript, as it heavily depends on the current used font, the fonts size, the elements width, floating elements (and probably the time of the day). Well, that's not entirely true: one could still calculate all those values and extract the first line, however doing so is a very cumbersome activity.
I guess the biggest difference is that "only one pseudo-element may appear per selector". The note says that this could be subject to change, but as of 2012 I don't believe we see any different behavior in the future (it's still in CSS4).
Example
The following example will add a language-tag to every quote on a given page using the pseudo-class :lang and the pseudo-element ::after:
q:lang(de)::after{
content: " (German) ";
}
q:lang(en)::after{
content: " (English) ";
}
q:lang(fr)::after{
content: " (French) ";
}
q:not(:lang(fr)):not(:lang(de)):not(:lang(en))::after{
content: " (Unrecognized language) ";
}
TL;DR
Pseudo-classes act as simple selectors in a sequence of selectors and thereby classify elements on non-presentational characteristics, pseudo-elements create new virtual elements.
References
W3C
Selectors Level 3
4. Selector syntax
6.6 Pseudo-classes
7. Pseudo-elements
CSS 2.1 Specification (outdated but still informative)
5.2 Selector syntax:
A simple selector is either a type selector or universal selector followed immediately by zero or more attribute selectors, ID selectors, or pseudo-classes, in any order. The simple selector matches if all of its components match.
5.10 Pseudo-elements and pseudo-classes
A pseudo-class filters existing elements.
a:link means all <a>s that are :link.
A pseudo-element is a new fake element.
div::after means non-existing elements after <div>s.
::selection is another example of a pseudo-element.
It doesn't mean all elements that are selected; it means the range of content that is selected, which may span portions of multiple elements.
Short description that helped me to understand the difference:
Pseudo-classes describe a special state.
Pseudo-elements match virtual elements.
From the Sitepoint docs:
A pseudo-class is similar to a class in HTML, but it’s not specified explicitly in the markup. Some pseudo-classes are dynamic—they’re applied as a result of user interaction with the document. - http://reference.sitepoint.com/css/pseudoclasses. These would be things like :hover, :active, :visited.
Pseudo-elements match virtual elements that don’t exist explicitly in the document tree. Pseudo-elements can be dynamic, inasmuch as the virtual elements they represent can change, for example, when the width of the browser window is altered. They can also represent content that’s generated by CSS rules. - http://reference.sitepoint.com/css/pseudoelements. These would be things like ::before, ::after, ::first-letter.
Below is the simple answer:
We use pseudo-class when we need to apply css based on the state of an element. Such as:
Apply css on hover of anchor element (:hover)
Apply css when gets focus on an html element (:focus). etc.
We use pseudo-element when we need to apply css to the specific parts of an elements or a newly inserted content. Such as:
Apply the css to first letter or first line of an element (::first-letter)
Insert content before, or after, the content of an element (::before, ::after)
Below is the example of both:
<html>
<head>
<style>
p::first-letter { /* pseudo-element */
color: #ff0000;
}
a:hover { /* pseudo-class */
color: red;
}
</style>
</head>
<body>
<a href="#" >This is a link</a>
<p>This is a paragraph.</p>
</body>
</html>
A conceptual answer:
A pseudo-element refers to things that are part of the document, but you just don't know it yet. For example the first letter. Before you only had text. Now you have a first letter that you can target. It is a new concept, but was always part of the document. This also includes things like ::before; while there isn't actual content there, the concept of something before something else was always there -- now you are specifying it.
A pseudo-class is state of something in the DOM. Just like a class is a tag you associate with an element, a pseudo-class is a class that gets associated by the browser or DOM or whatever, usually as a response to a change in state. When a user visits a link -- that link can take on the state of 'visited'. You can imagine the browser applying the class 'visited' to the Anchor element. :visited would then be how you select for that pseudo-class.
Pseudo-Class
A pseudo-class is way of selecting certain parts of a HTML document, based in principle not on the HTML document tree itself and its elements or on characteristics like name, attributes or contents, but on other phantom conditions like language encoding or the dynamic state of an element.
The original pseudo-class defined dynamic states of an element that are entered and exited over time, or through user intervention. CSS2 expanded on this concept to include virtual conceptual document components or inferred portions of the document tree e.g. first-child. Pseudo-classes operate as if phantom classes were added to various elements.
RESTRICTIONS: Unlike pseudo-elements, pseudo-classes can appear anywhere in selector chain.
Example pseudo-class code:
a:link /* This selects any "a" element whose target has not been visited.*/
{
padding : 4px;
text-decoration : none;
width : 10%;
color : #000000; /* black text color */
background-color : #99FF99; /* set to a pastel green */
border-top : 2px solid #ccffcc; /* highlight color */
border-left : 2px solid #ccffcc; /* highlight color */
border-bottom : 2px solid #003300; /* shadow color */
border-right : 2px solid #003300; /* shadow color */
}
a:visited /* This selects any "a" element whose target has been visited.*/
{ padding : 4px;
text-decoration : none;
color : #000000; /* black text color */
background-color : #ccccff; /* set to a lavender */
border-top : 2px solid #ffffff; /* highlight color */
border-left : 2px solid #ffffff; /* highlight color */
border-bottom : 2px solid #333366; /* shadow color *
border-right : 2px solid #333366; /* shadow color */
}
a:hover /* This selects any "a" element which is in a hover state. This is a state during pointer movement within the rendering region of an element. The user designates an element but does not activate it. */
{
color : #000000; /* black text color */
background-color : #99cc99; /* desaturated color */
border-top : 2px solid #003300; /* shadow color */
border-left : 2px solid #003300; /* shadow color */
border-bottom : 2px solid #ccffcc; /* highlight color */
border-right : 2px solid #ccffcc; /* highlight color */
}
a:focus /* This selects any "a" element which currently has focus. Focus is a state during which an element accepts keyboard input or other forms of text input. */
{
padding : 4px;
text-decoration : none;
width : 10%;
color : #000000; /* black text color */
background-color : #ffff99; /* set to a pastel yellow */
border-top : 2px solid #ffffcc; /* highlight color */
border-left : 2px solid #ffffcc; /* highlight color */
border-bottom : 2px solid #666633; /* shadow color */
border-right : 2px solid #666633; /* shadow color */
}
a:active /* This selects any "a" element which is in a state of activation. Active is a state during pointer activation (eg: press and release of a mouse) within the rendering region of an element.*/
{
padding : 4px;
text-decoration : none;
width : 10%;
color : #000000; /* black text color */
background-color : #ff99ff; /* set to a pink */
border-top : 2px solid #ffccff; /* highlight color */
border-left : 2px solid #ffccff; /* highlight color */
border-bottom : 2px solid #663366; /* shadow color */
border-right : 2px solid #663366; /* shadow color */
}
A page that demonstrates a rendering of the above pseudo-class code
Pseudo-elements
PSEUDO-ELEMENTS are used to address sub-parts of elements. They allow you to set style on a part of an element's content beyond what is specified in the documents. In other words they allow logical elements to be defined which are not actually in the document element tree. Logical elements allow implied semantic structure to be addressed in CSS selectors.
RESTRICTIONS: Pseudo-elements may only be applied to external and document-level contexts - not to in-line styles. Pseudo-elements are restricted in where they can appear in a rule. They may only appear at the end of a selector chain (after the subject of the selector). They should come after any class or ID names found in the selector. Only one pseudo-element can be specified per selector. To address multiple pseudo-elements on a single element structure, multiple style selector/declaration statements must be made.
Pseudo-elements can be used for common typographic effects such as initial caps and drop caps. They can also address generated content that is not in the source document (with the "before" and "after") An example style sheet of some pseudo-elements with properties and values added follows.
/* The following rule selects the first letter of a heading 1 and sets the font to 2em, cursive, with a green background. First-letter selects the first rendered letter/character for a block-level element. */
h1:first-letter {
font-size : 2em;
font-family : "Lucida Handwriting", "Lucida Sans", "Lucida Console", cursive;
background-color : #ccffcc;
}
/* The following rule selects the first displayed line in a paragraph and makes it bold. First-line selects the first rendered line on the output device of a block-level element. */
p:first-line {
font-weight : bold;
}
/* The following rule selects any content placed before a blockquote and inserts the phrase "Quote of the day:" in bold small caps with a green background. */
blockquote:before {
content : "Quote of the day:";
background-color : #ccffcc;
font-weight : bold;
font-variant : small-caps;
}
/* The following rule selects any content placed before a "q" element and inserts the smart open quote. */
q:before {
content : open-quote;
}
/* The following rule selects any content placed after a "q" element and inserts the smart close quote. */
q:after{
content : close-quote;
}
Sources:Link
In brief, from Pseudo-classes on MDN:
A CSS pseudo-class is a keyword added to a selector that specifies
a special state of the selected element(s). For example, :hover
can be used to apply a style when the user hovers over a button.
div:hover {
background-color: #F89B4D;
}
And, from Pseudo-elements on MDN:
A CSS pseudo-element is a keyword added to a selector that lets you
style a specific part of the selected element(s). For example,
::first-line can be used to style the first line of a paragraph.
/* The first line of every <p> element. */
p::first-line {
color: blue;
text-transform: uppercase;
}