'#' is the the ID selector, a fundamental part of the CSS language. It matches the HTML element with the given id. I know it but what is the main differences between using .classname {...} or #idselector in a .css file.
.hello { color:000000;}
or
#hello { color:000000;}
The first matches any element with the CSS class hello, the second matchs any element with the id value of hello. For example:
<div class="hello"></div>
<div id="hello"></div>
Precedence. IDs have a higher precedence then class selectors. If you had the following CSS:
.hello { color:#000000;}
#hello { color:#ff0000;}
Assuming the same element had the ID of 'hello' and class of 'hello' the font color of that element would be red since the ID has a higher precedence then the class selector.
Also, you can only have one element with the ID of 'hello' on a page. But you can have an unlimited number of elements with the class of 'hello'.
ID (#hello) should be used for unique, single elements only (for example: login button).
Class (.hello) should be used for elements that can be repeated (for example: navigation menu buttons).
IDs are unique, in a way that a certain element may only have one ID, and only one of the same ID may exist on a page. So the following is invalid:
<div id="first_id second_id"></div>
<div id="third_id"></div>
<div id="third_id"></div>
Classnames however are the exact opposite. A single element may have multiple classnames, and the same class name can appear multiple times in a document.
The purpose of IDs, is to signify unique parts of your webpage (i.e. the header, the main content div, the footer), or unique parts of your content (message-number-149632).
A classname's purpose, is to describe multiple same meaning objects. (i.e. dialog, post, menu-item).
In CSS, an #id has a higher specificity value, meaning that the following:
<div id="id" class="class">Test</div>
#id { background: red; }
.class { background: green; }
Will make the div red, because ID is more specific than class.
Related
I have written a CSS file to style a div with ID, inside another div with Classes. It looks like this
div.class1.class2 > div#ID1{
Styling Rules
}
But nothing is happening to DIV with ID1. Would appreciate any help and I can't change the structure of HTML or apply other IDs or classes to the elements.
<div class="class1 class 2">
<div id="ID1"></div>
</div>
IDs should only be used once, so if you followed that convention then you would simply target the ID in your selector and not concern yourself with the parent container it's in...
#id1 {
// code
}
But because of what you're asking implies that you have an ID being used more than once, I would suggest changing this to a class before moving forward; however, if you still wanted to keep your HTML the way it is, then you need to do this...
.class1 #id1 {
// code
}
Is there any difference between this
#id {
}
and this
div#id {
}
Yes. There is mainly two differences:
The first selector matches any element with id="id", while the second only matches div elements with that id.
The second selector is more specific, so if you have both and they match the same element, the styles from the second will have precedence.
Normally you would use the first selector. As the id should be unique in the page it would only target a single element.
The second selector would be useful if you use the same style sheet for several pages, and you either want to target the id under certain conditions, or if you want to override another rule by making it more specific.
The selectors behave differently:
#id is same as writing *#id (the asterisk selector is implied if tag name is omitted).
It matches any element that has an id of id.
div#id matches an element that is a div and has an id of id.
It is more specific than the above example.
In general, using #id selector is sufficient since ids are (supposed to be) unique inside a page. However, there are certain situations where you could use div#id.
Example 1
You use different elements for similar purpose therefore you want to assign them same id but style them differently, then you must be more specific:
<!-- page 1 -->
<ul id="features" title="All amenities">
<li>Spa</li>
<li>Pool</li>
</ul>
<!-- page 2 -->
<ol id="features" title="Top 3 amenities">
<li>Spa</li>
<li>Pool</li>
</ol>
Example 2
You can add a tag name to add weight to your selector. Consider this example:
<div id="header">
<img>
<div id="logo"><img></div>
<img>
</div>
/* file 1 */
#logo img { border: thin solid; }
/* file 2 */
#header img { border: 0; }
The first rule adds a thin border to images inside logo, the other rule removes border from all images inside header (including the one inside logo). In order to force the thin border rule you can change it to div#logo img so that it becomes more specific than the other rule.
Short answer: Yes.
#id {} targets a single ID selector wherever applied in a single HTML document. For example, <span id="id">...</span>, or <p id="id">...</p>
div#id {} will look for a <div> element that has an ID of #id, for example: <div id="id"></div> and cannot be used on any other tag except a <div>.
Note that ID selectors should only be used once semantically in a HTML document.
On a larger scale and more constructed case to this question, you should look at CSS Specificity; a well written and best-practise approach to specificity in CSS.
Also, take a look a CSSGuidelin.es, another well-written document on dealing with CSS selectors and their differences.
#elementid selector will select all elements having the id "elementid"
On the other hand, div#elementid selector will select only divs having id "elementid"
This question already has answers here:
What's the difference between an id and a class?
(17 answers)
Closed 5 years ago.
#main {
background: #000;
border: 1px solid #AAAAAA;
padding: 10px;
color: #fff;
width: 100px;
}
<div id="main">
Welcome
</div>
Here I gave an id to the div element and it's applying the relevant CSS for it.
OR
.main {
background: #000;
border: 1px solid #AAAAAA;
padding: 10px;
color: #fff;
width: 100px;
}
<div class="main">
Welcome
</div>
Now here I gave a class to the div and it's also doing the same job for me.
Then what is the exact difference between Id and class and when should I use id and when should I use class.? I am a newbie in CSS and Web-design and a little bit confused while dealing with this.
Use a class when you want to consistently style multiple elements throughout the page/site. Classes are useful when you have, or possibly will have in the future, more than one element that shares the same style. An example may be a div of "comments" or a certain list style to use for related links.
Additionally, a given element can have more than one class associated with it, while an element can only have one id. For example, you can give a div two classes whose styles will both take effect.
Furthermore, note that classes are often used to define behavioral styles in addition to visual ones. For example, the jQuery form validator plugin heavily uses classes to define the validation behavior of elements (e.g. required or not, or defining the type of input format)
Examples of class names are: tag, comment, toolbar-button, warning-message, or email.
Use the ID when you have a single element on the page that will take the style. Remember that IDs must be unique. In your case this may be the correct option, as there presumably will only be one "main" div on the page.
Examples of ids are: main-content, header, footer, or left-sidebar.
A good way to remember this is a class is a type of item and the id is the unique name of an item on the page.
ids are unique
Each element can have only one id
Each page can have only one element with that id
classes are NOT unique
You can use the same class on multiple elements.
You can use multiple classes on the same element.
Javascript cares
JavaScript people are already probably more in tune with the differences between classes and ids. JavaScript depends on there being only one page element with any particular id, or else the commonly used getElementById function couldn't be depended on.
For more info on this click here.
Example
<div id="header_id" class="header_class">Text</div>
#header_id {font-color:#fff}
.header_class {font-color:#000}
(Note that CSS uses the prefix # for IDs and . for Classes.)
However color was an HTML 4.01 <font> tag attribute deprecated in HTML 5.
In CSS there is no "font-color", the style is color so the above should read:
Example
<div id="header_id" class="header_class">Text</div>
#header_id {color:#fff}
.header_class {color:#000}
The text would be white.
IDs must be unique--you can't have more than one element with the same ID in an html document. Classes can be used for multiple elements. In this case, you would want to use an ID for "main" because it's (presumably) unique--it's the "main" div that serves as a container for your other content and there will only be one.
If you have a bunch of menu buttons or some other element for which you want the styling repeated, you would assign them all to the same class and then style that class.
As pretty much everyone else has said use ID for one-off elements and class for multiple use elements.
Here is a quick, over simplified example, take HTML and HEAD tags as read
<body>
<div id="leftCol">
You will only have one left column
</div>
<div id="mainContent">
Only one main content container, but.....
<p class="prettyPara">You might want more than one pretty paragraph</p>
<p>This one is boring and unstyled</p>
<p class="prettyPara">See I told you, you might need another!</p>
</div>
<div id="footer">
Not very HTML5 but you'll likely only have one of these too.
</div>
</body>
Also, as mentioned in other answers ID are well exposed to javascript, classes less so. However modern javascript frameworks like jQuery leverage class for javascript too
ID's have the functionality to work as links to particular sections within a webpage.
a keyword after # tag will take you to a particular section of the webpage.
e.g "http://exampleurl.com#chapter5" in the address bar will take you there when you have a "section5" id wrapped around the chapter 5 section of the page.
The class attribute can be used with multiple HTML elements/tags and all will take the effect. Where as the id is meant for a single element/tag and is considered unique.
Moreoever the id has a higher specificity value than the class.
id:
It will identify the unique element of your entire page. No other element should be declared with the same id.
The id selector is used to specify a style for a single, unique element.
The id selector uses the id attribute of the HTML element, and is defined with a "#".
class:
The class selector is used to specify a style for a group of elements. Unlike the id selector, the class selector is most often used on several elements.
This allows you to set a particular style for many HTML elements with the same class.
The class selector uses the HTML class attribute, and is defined with a "."
If there is something to add to the previous good answers, it is to explain why ids must be unique per page. This is important to understand for a beginner because applying the same id to multiple elements within the same page will not trigger any error and rather has the same effects as a class.
So from an HTML/CSS perspective, the uniqueness of id per page does not make a sens. But from the JavaScript perspective, it is important to have one id per element per page because getElementById() identifies, as its name suggests, elements by their ids.
So even if you are a pure HTML/CSS developer, you must respect the uniqueness aspect of ids per page for two good reasons:
Clarity: whenever you see an id you are sure it does not exist elsewhere within the same page
Scalability: Even if you are developing only in HTML/CSS, you need to take in consideration the day where you or an other developer will move on to maintain and add functionality to your website in JavaScript.
You can assign a class to many elements. You can also assign more than one class to an element, eg.
<button class="btn span4" ..>
in Bootstrap. You can assign the id only to one.
So if you want to make many elements look the same, eg. list items, you choose class. If you want to trigger certain actions on an element using JavaScript you will probably use id.
A class can be used several times, while an ID can only be used once, so you should use classes for items that you know you're going to use a lot. An example would be if you wanted to give all the paragraphs on your webpage the same styling, you would use classes.
Standards specify that any given ID name can only be referenced once within a page or document. Use IDs when there is only one occurence per page. Use classes when there are one or more occurences per page.
This is very simple to understand :-
id is used when we have to apply CSS property to one attribute only.
class is used when we have to use CSS property in many locations within the same page or different.
General :- for unique structure like staring div and buttons layout we use id .
for same CSS throughout the page or project we use class
id is light and class is little heavy
A simple way to look at it is that an id is unique to only one element.
A class is not unique and applied to multiple elements.
For example:
<p class = "content">This is some random <strong id="veryImportant"> stuff!</strong></p>
Content is a class since it'll probably apply to some other tags aswell where as "veryImportant" is only being used once and never again.
Unlike the id selector, the class selector is most often used on several elements.
This allows you to set a particular style for many HTML elements with the same class.
The class selector uses the HTML class attribute, and is defined with a "."
A simple way to look at it is that an id is unique to only one element. class is better to use as it will help you to execute what ever you want.
id selector can be used to more elements. here is the example:
css:
#t_color{
color: red;
}
#f_style{
font-family: arial;
font-size: 20px;
}
html:
<p id="t_color"> test only </p>
<div id="t_color">the box text</div>
I tested on internet explorer (ver. 11.0) and Chrome (ver.47.0). it works on both of them.
The "unique" only means one element can not have more than one id attributes like class selector. Neither
<p id="t_color f_style">...</p>
nor
<p id="t_color" id="f_style">...</p>
I was at w3schools.com learning html and their code examples included the word "class" such as <div class="page"> . They didn't explain it so i needed you guys to. So please define what class in <div class="page"> means.
A class is a non-unique identifier for HTML elements. It can be used in a variety of ways:
1. For styling of those elements with CSS.
To apply a group of CSS properties as a pack to all elements of the class.
.page
{
border: solid 1px #009900;
padding: 5px;
color: #000077;
}
You can apply it like this:
<div class="page">
<ul class="page">
Ans so on.
You can also restrict it to only be valid for a specific element type, for example, only for divs:
div.page
{
/* ... */
}
2. For accessing these elements with JavaScript.
To perform some manipulations with all elements of the class. Like this:
$('.advancedOption').attr("disabled", true);
3. For some internal operations in browser. Beyond the scope of this question.
A class is best thought of as a 'category' or 'type'. This is best demonstrated with an example.
Let's say you have an HTML page that will have a table of products. In that table, you will have the products name, description, etc. Now, suppose you wanted ALL the products name to be styled a specific way.
<p class='product-standard'>This is a product name</p>
Then with your CSS you can do something like this:
p.product-standard { color:gray; }
So now, all tags with the class 'product-standard' will be gray.
Now, if you want certain sale items to be red, you can do this:
<p class='product-sale'>Sale item</p>
and
p.product-sale {color:red}
Classes allow you have consistent styling across many html tags.
The attribute class refers to a CSS class.
For example, in HTML:
<div class="page">
will refer to the CSS code:
div.page {
some css properties
}
MSDN is the best place to look for -
CLASS Attribute - Basically its a string or attribute that specifies or receives the class or css style rule.
It's just a space-separated list of words you associate with the element that can be used to select it for styling or with a script. A class by itself doesn't do anything — it's like a tag on a blog post.
If you're familiar with the idea of a class in programming, it has nothing to do with that.
A class in html is an attribute you can add to any html element (like paragraphs, links). You can make up the name yourself (has to start with a letter though), and then stylesheets or javascript can do something with that specific element.
For instance:
<p>This is a paragraph with no class</p>
<p class="foo">This paragraph has a class named "foo"</p>
<span class="foo">This span has a class as well
Now if you apply CSS to style your html, you can use:
p { color: blue }
p.foo { color: red }
span.foo { color: green }
.foo { font-size: big }
This way all paragraphs have blue text, except the paragraph with the class 'foo'. The rule p.foo effects only paragraphs with the class foo. The rule span.foo applies only to span elements with the class foo, so that part will have green text. Then finally, the .foo rule applies to all elements with the 'foo' class, so the last two elements will have big-sized text.
You can also have multiple classes. <div class="foo bar"> has the classes foo and bar. You can access those separately in the CSS by using .foo or .bar
i know it is a very old question but i hope my answer helps any newbie who comes here searching for a simplified answer.
in brief,
you may consider the class as a set of names for the element.
those names you may use any of them to call the element anytime on the same page.
it can be used to select the element to style it, change it, add some behavior for it, and/or remove it.
example:
<div class="sara"></div>
this sara element can be selected in css like the following ex:
<style>
.sara{color:red}
</style>
or in javascript like the following ex:
<script>
document.querySelector('.sara').remove()
</script>
I hope this simplified answer helps
This question already has answers here:
What's the difference between an id and a class?
(17 answers)
Closed 9 years ago.
Where can I use ids and classes? What is the difference between them? Is there any need that we should compulsorily use ids in our CSS?
IDs are meant to be unique, while classes are better for a "type" of element.
So you might have something like:
<ul id="menu">
....
</ul>
Because you will probably only have 1 main menu on your site.
For classes, however, you might have something like:
<span class='author'>Paolo Bergantino</span>
Or perhaps to style the div that contains an answer on this site:
<div class='answer'>....</div>
Because there will be multiple of these per page, they are a class of elements. Think of an ID as the social security number of an element. Whenever an element is important enough and is unique, you give it an ID. This also helps with dynamic websites as selecting elements by ID is by far the fastest way, and if you have multiple elements with the same ID (thus violating this practice) Javascript won't work as intended.
An ID identifies exactly one DOM element, uniquely. A class identifies a group of related DOM elements.
For example, you might have a single, unique nav menu, identified by an ID:
<div id="nav">...</div>
and within it have a number of menu sets, each of which is also uniquely identified and which belongs to a common class:
<div id="nav">
<ul id="content_menu" class="menu">...</ul>
<ul id="contact_menu" class="menu">...</ul>
<ul id="personal_menu" class="menu">...</ul>
</div>
Short and simple:
Classes may be used as many times as needed (and are defined by a period).
Ids can only be used on ONE element (and are defined by a pound).
<style>
.class {
font-size: 3em;
}
#id {
font-size: 3em;
}
</style>
<body>
<span class="class">I am a class</span>
<span class="class">Look at me, also a class</span>
<span id="id">I am special, you can only have one of me or I do not meet XHTML standards</span>
From the w3schools:
The id attribute specifies a unique id
for an HTML element.
The id must be unique within the HTML
document.
The id attribute can be used by a
JavaScript (via the HTML DOM) or by
CSS to make changes or style the
element with the specified id.
and
The class attribute specifies a
classname for an element.
The class attribute is mostly used to
point to a class in a style sheet.
However, it can also be used by a
JavaScript (via the HTML DOM) to make
changes to HTML elements with a
specified class.
The class attribute cannot be used in
the following HTML elements: base,
head, html, meta, param, script,
style, and title.
It is possible to assign multiple
classes to one HTML element, e.g.
.
This allows you to combine several CSS
classes for one HTML element.
While you could use classes for everything, the separation between "classes that only occur once" (i.e. IDs) and "regular classes" is quite useful for keeping your CSS meaningful for yourself.
.menu { ... } /* Err, how many of those did I have? */
#menu { ... } /* Ahh, THE menu. */
An ID refers to a specific element (every ID should never used more than once); a class refers to multiple elements.