The document discusses different types of CSS selectors that can be used to select and style elements in an HTML document. It covers element selectors, class selectors, ID selectors, attribute selectors, and pseudo-class selectors. Examples are provided for each type of selector to demonstrate how they can be used to select elements and apply CSS styles. Combinators are also discussed, which allow selecting elements based on a specific relationship between them. In summary, the document provides an overview of CSS selector syntax and examples of how different selector types can be used to target elements in an HTML document for styling purposes.

1. BEN KHALFALLAH HÉLA
CSSpatternmatchingrulestoselectelementsinthe
documenttree
CSSSELECTORS
2022

2. CSSRULESTRUCTURE
selector color : red ; background : yellow ; }
{
HTML TAG, CLASS NAME, UNIVERSAL SELECTOR (*)
PROPERTY
VALUE
DECLARATION
DECLARATION BLOCK
PROPERTY
VALUE
DECLARATION

3. SELECTORSTYPES
Element selectors
Class selectors
ID selectors
Attribute selectors
Combinators
Pseudo-class selectors
Pseudo-elements selectors

4. ELEMENTSELECTORS
element { property: value; property: value; }
Any (valid) html tag
h2 { color: silver; } Make the text of all h2 elements in the html
document appear in silver.
h1 { color: gray; }
h2 { color: gray; }
h3 { color: gray; }
h4 { color: gray; }
h5 { color: gray; }
h6 { color: gray; }
h1, h2, h3, h4, h5, h6 {
color: gray;
}
GROUPING SELECTORS
h1 { font: 18px Helvetica; }
h1 { color: purple; }
h1 { background: aqua; }
h1 {
font: 18px Helvetica;
color: purple;
background: aqua;
}
GROUPING DECLARATIONS

5. CLASSSELECTORS
.class-name { property: value; property: value; }
<p class="legal-notice--description">
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.
</p>
<span>
Contrary to popular belief, Lorem Ipsum is not simply random text
</span>
<p class="legal-notice--description">
Sed ut perspiciatis unde omnis iste natus error sit voluptatem accusantium
doloremque laudantium, totam rem aperiam, eaque ipsa quae ab illo inventore
veritatis et quasi architecto beatae vitae dicta sunt explicabo.
</p>
.legal-notice--description{
font: 18px Helvetica;
color: purple;
background: aqua;
}
HTML :
CSS :
The css styling will only be applied to the element that has a
class attribute with a value of 'legal-notice--description'.
CASE SENSITIVE SELECTOR

6. COMBININGELEMENTANDCLASSSELECTORS
element.class-name { property: value; property: value; }
p.legal-notice--description{
font-weight: bold;
}
Rule applies only to a speci
fi
c type of element/class combination, it does
not leak over to other elements.
<p class="legal-notice--description">
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.
</p>
<span class="legal-notice--description">
Contrary to popular belief, Lorem Ipsum is not simply random text
</span>
<p class="legal-notice--description">
Sed ut perspiciatis unde omnis iste natus error sit voluptatem accusantium
doloremque laudantium, totam rem aperiam, eaque ipsa quae ab illo inventore
veritatis et quasi architecto beatae vitae dicta sunt explicabo.
</p>
The selector will match this element (p having a class with the
value ‘legal-notice—description’).
The selector will match this element (p having a class with the
value ‘legal-notice—description’).
The selector will not match this element (span).
CASE SENSITIVE SELECTOR

7. MULTIPLECLASSESSELECTORS
.class-name-1.class-name-2….. { property: value; property: value; }
.alert {
font-size: 18px;
}
.error{
background-color: red;
}
.message--body{
font-size: 25px;
}
.alert.error{
font-weight: bold;
}
.alert.error.message--body{
background: white;
}
p.alert.error{
font-weight: lighter;
}
<span class="alert error">
This will match the .alert.error selector
</span>
<span class="error alert">
This will also match the .alert.error selector (order does not matter)
</span>
<span class="alert">
This will match .alert selector
</span>
<span class="error">
This will match .error selector
</span>
<span class="alert error message--body">
This will match .alert.error.message--body selector
</span>
<p class="alert error">
This will match the p.alert.error selector
</p>
The selector will match in any order, but the order in which the style
is applied will change (especially for common properties).
HTML :
CSS :
CASE SENSITIVE SELECTOR

8. IDSELECTORS
#html-id-value { property: value; property: value; }
#article-title {
font-size: 30px;
font-weight: bold;
background: gainsboro;
}
#article-description{
font-size: 18px;
font-weight: lighter;
background: white;
}
HTML :
CSS :
<h4 id="article-title">
1914 translation by H. Rackham
</h4>
<p id="article-description">
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna
aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco
laboris nisi ut aliquip ex ea commodo consequat.
</p>
ID selectors can’t be combined with other IDs.
id attribute must match exactly the value given in the selector.
There should be only one element with a given ID in a document.
CASE SENSITIVE SELECTOR
IT’S NOT RECOMMENDED TO USE ID
SELECTORS, THEY ARE LESS FLEXIBLE,
HARD TO OVERRIDE (HIGHER SPECIFICITY
THAN CLASSES).

9. ATTRIBUTESELECTORS
Match elements that have a certain attribute with any value :
p[class]{
color: purple;
}
Select all p elements that
have a class attribute with
any value and make their text
color purple.
a[href][title]{
color: green;
}
<p class="error">Oups, this page is not available !</p>
Html tag (element)
Attribute
Content
attribute-name="attribute-value"
= End of html tag
<a
href="https://example.com"
title="Example Home Page"
>
Website (with title)
</a>
<a
href="https://new-site.com"
title="New Site Page"
>
New Website (with title)
</a>
Select any html hyperlink that has both an href and a title attribute (with any value) and make their
text color green.
<a
href="https://my-site.org"
>
Website (without title)
</a>
<a
title="This is not a link"
>
Incorrect link !
</a>

10. ATTRIBUTESELECTORS
Match elements that have a certain attribute with an exact value :
<p class="error">Oups, this page is not available !</p>
Html tag (element)
Attribute
Content
attribute-name="attribute-value"
= End of html tag
p[class="error"]{
color: purple;
}
Select all p elements that
have a class attribute with
exactly the value ‘error’ and
make their text color purple.
<a
href="https://example.com"
title="Example Home Page"
>
Website (with title)
</a>
a[href="https://example.com"][title="Example Home Page"]{
color: green;
}
CASE SENSITIVE SELECTOR
<a
href="https://new-site.com"
title="New Site Page"
>
New Website (with title)
</a>
<a
href="https://my-site.org"
>
Website (without title)
</a>
<a
title="This is not a link"
>
Incorrect link !
</a>
Select any html hyperlink that has an href attribute with exactly the value ‘https://example.com’ and a
title attribute with exactly the value ‘Example Home Page’ and make their text color green.

11. ATTRIBUTESELECTORS
Matching one word in a space-separated list (~) :
CASE SENSITIVE SELECTOR
<p
class="alert urgent info"
>
The is an information message!
</p>
<p
class="alert urgent warning"
>
The resource took too long to load!
</p>
<p
class="alert urgent error"
>
The service is unavailable at the moment
</p>
p[class~="alert"] {
color: purple;
font-weight: bold;
font-size: 18px;
}
p[class~="warning"] {
color: orange;
font-size: 12px;
}
p[class~="error"] {
color: red;
}
Select all p elements whose class attribute contains the word ‘alert’.
Select all p elements whose class attribute contains the word ‘warning’.
Select all p elements whose class attribute contains the word ‘error’.
a[title~="Nasa"] {
color: green;
font-weight: light;
font-size: 15px;
}
<a
href="https://www.nasa.gov/missions"
title="Nasa Missions Page"
>
Nasa Missions Page
</a>
<a
href="https://www.nasa.gov/"
title="Nasa Home Page"
>
Nasa Home Page
</a>
<a
href="https://www.spacex.com/"
title="Space X Home Page"
>
Space X Home Page
</a>
Space separated list
Space separated list
Space separated list
title="Nasa Missions Page"
title="NasaMissions Page"
title="Nasa-Missions Page"
THE ORDER OF SELECTORS MATTER !
The word only matches inside a space-separated list (case sensitive).
title="nasa Missions Page"

12. ATTRIBUTESELECTORS
Matching a substring within an attribute value (*) :
CASE SENSITIVE SELECTOR
THE ORDER OF SELECTORS MATTER !
<h4 class="article-details article-title">
1914 translation by H. Rackham
</h4>
<p class="article-details article-description">
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi
ut aliquip ex ea commodo consequat.
</p>
<img
class="article-image"
alt="mission"
src="https://science.nasa.gov/files/science-pink/s3fs-public/styles/
large/public/thumbnails/image/ACE_0.jpg?itok=t2wtXFRN"
/>
h4[class*="details"] {
color: blue;
font-weight: bold;
font-size: 25px;
}
p[class*="details"] {
color: darkgray;
font-weight: light;
font-size: 15px;
}
*[class*="details"] {
text-decoration: underline;
}
*[class*="image"] {
width: 10rem;
height: 10rem;
}
Select all h4 elements whose class attribute contains the
substring ‘details’.
Select all p elements whose class attribute contains the
substring ‘details’.
Select all elements whose class attribute contains the
substring ‘details’.
Select all elements whose class attribute contains the
substring ‘image’.
h4[class~="details"] {
color: blue;
font-weight: bold;
font-size: 25px;
}
~ doesn’t much substring but one word in a
space-separated list.
input[title*="format"] {
background-color: red;
}
<input
type="tel"
title="Telephone number should be formatted as XXX-XXX-XXXX"
pattern="d{3}-d{3}-d{4}"
/>
<input
type="email"
title="Email is a mandatory field"
required
/>
img[class*="image"][alt*="details"] {
width: 20rem;
height: 20rem;
}
img[class~="article-image"][alt*="details"] {
width: 20rem;
height: 20rem;
}
Combining selectors

13. ATTRIBUTESELECTORS
Matching a substring at the beginning of an attribute value (^) :
CASE SENSITIVE SELECTOR
<img
class="article-details article-image"
alt="ps5-console"
src="https://pbs.twimg.com/media/EiGQrbFXsAAzrpq?format=jpg&name=small"
/>
<img
class="article-details article-image"
alt="xbox-activision"
src="https://image.jeuxvideo.com/medias-md/164253/1642526486-8301-card.jpg"
/>
<img
class="article-details article-image"
alt="xbox-serie-x"
src="https://static.actu.fr/uploads/2019/04/8c976cba-12d8-42ca-b419-c177f84b66bf.jpg"
/>
<img
class="article-details article-image"
alt="kindle-paperwhite"
src="https://img.20mn.fr/zBDkMRUzTDerDDNSZYSbWSk/648x415"
/>
img[alt^="xbox"] {
width: 30rem;
height: 30rem;
border: 2px solid red;
}
Selecting all img elements whose alt attribute starts with ‘xbox’.
<img
class="article-details article-image"
alt="xbox-activision game"
src="https://image.jeuxvideo.com/medias-md/164253/1642526486-8301-card.jpg"
/>
<img
class="article-details article-image"
alt="game xbox-serie-x"
src="https://static.actu.fr/uploads/2019/04/8c976cba-12d8-42ca-b419-c177f84b66bf.jpg"
/>
*[class^="alert"] {
border: 2px solid red;
}
<span class="alert error">
This will match the selector
</span>
<span class="error alert">
This will not match the selector
</span>
<p class="alert">
This will match the selector
</p>
<span class="alerterror">
This will match the selector
</span>
<span class="alert-error">
This will match the selector
</span>
<p class="Alert">
This will match the selector
</p>

14. ATTRIBUTESELECTORS
Matching a substring at the end of an attribute value ($) :
CASE SENSITIVE SELECTOR
<img
alt="X-ray glow"
src="https://www.sciencenews.org/wp-content/uploads/2022/01/012022_LK_COW_feat-1030x580.jpg"
/>
<img
alt="Neutron star collisions"
src=« https://www.sciencenews.org/wp-content/uploads/2021/11/110221_ec_heavy-elements_feat-1030x580.gif"
/>
<img
alt="Intense drought or flash floods"
src="https://www.sciencenews.org/wp-content/uploads/2022/01/011421_CG_flooding_feat-1030x580.png"
/>
<img
alt="The first magnetar flare"
src="https://www.sciencenews.org/wp-content/uploads/2021/01/011421_lg_magnetar_feat-1030x580.jpg"
/>
img[src$=".jpg"] {
width: 10rem;
height: 10rem;
border: 2px solid red;
}
img[src$=".png"] {
width: 15rem;
height: 15rem;
border: 2px solid yellow;
}
a[href$=".pdf"] {
border: 2px solid purple;
}
<a
href="https://cfm.ehu.es/ricardo/docs/python/Learning_Python.pdf"
title="Learning Python"
>
Learning Python
</a>
<a
href="https://cfm.ehu.es/ricardo/docs/python/Learning_Python.PDF"
title="Learning Python"
>
Learning Python
</a>
<a
href="https://cfm.ehu.es/ricardo/docs/python/Learning_Python.csv"
title="Learning Python"
>
Learning Python Stats
</a>

15. ATTRIBUTESELECTORS
Case insensitive identi
fi
er (i) :
a[href$=".pdf" i] {
border: 2px solid purple;
}
<a
href="https://cfm.ehu.es/ricardo/docs/python/Learning_Python.pdf"
title="Learning Python"
>
Learning Python
</a>
<a
href="https://cfm.ehu.es/ricardo/docs/python/Learning_Python.PDF"
title="Learning Python"
>
Learning Python
</a>
a[title~="Nasa" i] {
color: green;
font-weight: light;
font-size: 15px;
}
<a
href="https://www.nasa.gov/"
title="Nasa Home Page"
>
Nasa Home Page
</a>
<a
href="https://www.nasa.gov/missions"
title="nasa Misions Page"
>
Nasa Misions Page
</a>
input[title*="format" i] {
background-color: red;
}
<input
type="tel"
title="Phone number should be formatted as XXX-XXX-XXXX"
pattern="d{3}-d{3}-d{4}"
/>
<input
type="tel"
title="phone number should be Formatted as XXX-XXX-XXXX"
pattern="d{3}-d{3}-d{4}"
/>

16. ATTRIBUTESELECTORS(RECAP)
[my-attribute="attribute-value"]
Select any element with an attribute 'my-attribute'
whose value is exactly equal to ‘attribute-value'.
[my-attribute~="attribute-value"]
Select any element with an attribute ‘my-attribute’
whose value contains the word ‘attribute-value’ in
a space-separated list of words.
[my-attribute*="attribute-value"]
Select any element with an attribute 'my-attribute'
whose value contains the substring ‘attribute-
value'.
[my-attribute^="attribute-value"]
Select any element with an attribute 'my-attribute'
whose value begins with ‘attribute-value'.
[my-attribute$="attribute-value"]
Select any element with an attribute 'my-attribute'
whose value end with ‘attribute-value'.
[my-attribute="attribute-value" i] Case insensitive identi
fi
er (i)

17. DESCENDANTCOMBINATOR
selector1 selector2 { property: value; }
div span {
color: red;
}
Set the text color to red for any span
element descending from div
<div>
<h4>
1914 translation by H. Rackham
</h4>
<span>
1. This will match
</span>
<span>
<span>
2. This will match
</span>
</span>
</div>
<div>
<p>
<span>3.This will match</span>
</p>
</div>
.article-details span {
color: red;
}
Selector can be class names
<div className="article-details">
<span>
<span>
1. This will match
</span>
</span>
<p>
<span>
<span>
2. This will match
</span>
</span>
</p>
</div>

18. CHILDCOMBINATOR
selector1 > selector2 { property: value; }
div > span {
color: red;
}
Set the text color to red for any span
element descending from div
<div>
<h4>
1914 translation by H. Rackham
</h4>
<span>
1. This will match
</span>
<span>
<span>
2. This will match
</span>
</span>
</div>
<div>
<p>
<span>3.This will not match</span>
</p>
</div>
( stricter than the descendant combinator )
Elements matched by the second selector must be the immediate
children of the elements matched by the
fi
rst selector :
.article-details > span {
color: red;
}
Selector can be class names
<div>
<h4>
1914 translation by H. Rackham
</h4>
<span>
1. This will not match
</span>
<div className="article-details">
<span>
<span>
2. This will match
</span>
</span>
</div>
</div>
<div>
<p>
<span>3.This will not match</span>
</p>
</div>

19. ADJACENTSIBLINGCOMBINATOR
former_element + target_element { property: value; }
Select an element that immediately follows another element with the same parent :
h1 + p {
margin-top: 0;
}
Remove the top margin from a paragraph
immediately following an h1 .
Select any p element that immediately follows an h1
element that shares a parent with the p element.
<div>
<h1>
1914 translation by H. Rackham
</h1>
<p>
This paragraph will match
</p>
<p>
This will not match
</p>
</div>
This p isn’t immediately after h1.

20. GENERALSIBLINGCOMBINATOR
former_element ~ target_element { property: value; }
Select an element that follows another element when both elements share the same parent :
h2 ~ ol {
font-style: italic;
}
The two elements do not need to be adjacent sibling.
Italicize any ol element that follows an h2 element
and also share a parent with h2.
<div>
<h2>
1914 translation by H. Rackham
</h2>
<p>
Contrary to popular belief, Lorem Ipsum is not simply random text.
</p>
<ol>
<li>1. This will match</li>
<li>2. This will match</li>
<li>3. This will match</li>
</ol>
<p>
Contrary to popular belief, Lorem Ipsum is not simply random text.
</p>
<ol>
<li>4. This will match</li>
<li>5. This will match</li>
<li>6. This will match</li>
</ol>
<div>
<ol>
<li>1. This will not match</li>
<li>2. This will not match</li>
<li>3. This will not match</li>
</ol>
</div>
</div>
Follows h2 + shares the same parent
Follows h2 + shares the same parent
Follows h2 but doesn’t shares the same parent

21. SELECTINGEMPTYELEMENTS
element:empty { property: value; }
Select any element that has no children of any kind, including text nodes (text and whitespace) :
<div>
<p></p>
<p> </p>
<p>
</p>
<p><!--This is a comment--></p>
</div>
This will match
This will not match (white space)
This will not match
This will match (comments are not considered content).
*: empty { display:none;} can hide elements like input,
img, text area, because they don’t have children.
p:empty {
display: none;
}

22. SELECTINGUNIQUECHILDREN
Select elements when they are the only child element of another element :
element:only-child { property: value; }
img:only-child {
border: 1px solid red;
}
<a href="http://w3.org/">
<img
src="w3.png"
alt="W3C"
/>
</a>
<a href="http://w3.org/">
<img
src="w3.png"
alt="W3C"
/>
<em>The W3C</em>
</a>
This will match : img is the only child of a.
This will not match : img isn’t the only child of a.
Select img that are the only child.
<ol>
<li>
First
<ul>
<li>This list has just one element.</li>
</ul>
</li>
<li>
Second
<ul>
<li>This list has three elements.</li>
<li>This list has three elements.</li>
<li>This list has three elements.</li>
</ul>
</li>
</ol>
li:only-child {
color: red;
list-style-type: square;
}

23. SELECTINGFIRSTCHILDREN
Select elements that are the
fi
rst children of others elements :
element:
fi
rst-child { property: value; }
<div>
<p>This text is selected!</p>
<p>This text isn't selected.</p>
</div>
<div>
<h2>This text isn't selected: it's not a `p`.</h2>
<p>This text isn't selected.</p>
</div>
p:first-child {
color: lime;
background-color: black;
padding: 5px;
}
ul li:first-child {
color: red;
font-weight: bold;
}
<ul>
<li>Item 1</li>
<li>Item 2</li>
<li>
Item 3
<ul>
<li>Item 3.1</li>
<li>Item 3.2</li>
<li>Item 3.3</li>
</ul>
</li>
</ul>

24. SELECTINGLASTCHILDREN
Select elements that are the last children of others elements :
element:last-child { property: value; }
<div>
<p>This text isn't selected.</p>
<p>This text is selected!</p>
</div>
<div>
<p>This text isn't selected.</p>
<h2>This text isn't selected: it's not a `p`.</h2>
</div>
p:last-child {
color: lime;
background-color: black;
padding: 5px;
}
<ul>
<li>Item 1</li>
<li>Item 2</li>
<li>
Item 3
<ul>
<li>Item 3.1</li>
<li>Item 3.2</li>
<li>Item 3.3</li>
</ul>
</li>
</ul>
ul li:last-child {
border: 1px solid red;
color: red;
}

25. SELECTINGEVERYnthCHILDREN
Select elements based on their position among a group of siblings :
element:nth-child(number) { property: value; }
element:nth-child(odd) { property: value; }
element:nth-child(even) { property: value; }
element:nth-child(a * n + b) { property: value; }
element:nth-last-child(number) { property: value; }
element:nth-last-child(odd) { property: value; }
element:nth-last-child(even) { property: value; }
element:nth-last-child(a * n + b) { property: value; }
Count start from top to bottom Count start from bottom to top
n starts from 0 n starts from 0

26. NEGATIONPSEUDO-CLASS
element:not(selector) { property: value; }
.moreinfo:not(li) {
font-style: italic;
}
Select all elements with a class whose value contains the word
‘moreinfo’ as long as they are not li elements
p:not(:not(p))
Cannot be nested
*.article-link:not(li):not(p){
color: red;
}
Select all elements with class ‘article-link’ that are neither list items
nor paragraphs.

27. HYPERLINKPSEUDO-CLASSES
:link Matches links that have not yet been visited.
:visited Matches links that have been visited.
a:link{
color: blue;
}
a:visited{
color: red;
}
a.article-details-link:link, a[href^="http"]:link {
color: slateblue;
}
a.article-details-link:visited, a[href^="http"]:visited {
color: maroon;
}
a#article-link-id:link {
color: yellow;
}
a#article-link-id:visited {
color: gray;
}
Class name selectors Element ID selectors

28. USERACTIONPSEUDO-CLASSES
:hover Matches when an element is hovered.
:active
Matches when an item is being activated by the
user, for example clicked on.
:focus Matches when an element has focus.

29. UI-STATEPSEUDO-CLASSES
:enabled Represents a user interface element that is in an enabled state.
:disabled Represents a user interface element that is in a disabled state.
:read-only Represents any element that cannot be changed by the user.
:read-write Represents any element that is user-editable.
:checked
Matches when elements such as checkboxes and radiobuttons are
toggled on.
:indeterminate Matches when UI elements are in an indeterminate state.
:default
Matches one or more UI elements that are the default among a set of
elements.
:valid Matches an element with valid contents.
:invalid Matches an element with invalid contents.
:in-range
Applies to elements with range limitations, for example a slider control,
when the selected value is in the allowed range.
:out-of-range
Applies to elements with range limitations, for example a slider control,
when the selected value is outside the allowed range.
:required Matches when a form element is required.
:optional Matches when a form element is optional.

30. BEFORE&AFTERPSEUDOELEMENTSSELECTORS
::before
Inserts something before the content of each selected
element(s).
p::before {
content: "Read this: ";
}
::after
Inserts something after the content of each selected
element(s).
p::after {
content: " - Remember this";
}

31. FIRSTLETTERPSEUDOELEMENTSELECTOR
p::first-letter{
color: red;
}
p:first-of-type::first-letter{
font-size: 200%;
}

32. FIRSTLINEPSEUDOELEMENTSELECTOR
p::first-line{
font-size: 150%;
color: purple;
}