In this example:
http://jsfiddle.net/Ja29K/
<style>
/* Default links */
a {
color: #0F0; /* Green */
}
/* Header links */
#header a {
color: #F00; /* Red */
}
/* Login link */
#login {
color: #00F; /* Blue */
}
</style>
<header id="header">
<p>header link is red</p>
<p><a id="login" href="#">login link</a> is not blue</p>
</header>
Is not logical that the login link must be blue?
I know that the declarations have the same origin and same importance, so they need to be scored (selector's specificity).
To calculate selector specificity I created an table for each selector:
A = Number of inline styles: 0
B = Number of ID: 0
C = Number of classes: 0
D = Number of elements: 0
So the login element have 3 collisions related to his color: a, #header a, #login
element (A, B, C, D)
a (0, 0, 0, 1) = 1
#header a (0, 1, 0, 1) = 101
#login (0, 1, 0, 0) = 100
The selector "#header a" wins because it had the biggest score.
But
If we change the selector "#login" to "a#login", we will have:
a#login (0, 1, 0, 1) = 101
The selector "#header a" looses, because with a draw wins the last that was declared.
So, the thing that I can't understand is:
Since "#header a" selector refers to many elements and an ID selector (e.g. #login) just refer one element, is logical that we want to apply ID selector declarations to that element, right? I really can't understand this CSS precedence logic, because I think ID selector must be basically the most specific thing possible, just like inline styles.
P.S.: Sorry for my bad english :)
No, according to the logic of selectors, it is not.
#header a is more specific than #login. If you reduced your #header a selector to #header, then the header selector and the login selector would have the same specificity, and the rule that was last expressed (in your order the color from login) would be used. The same would be true if you increased the specificty of the login selector by adding a tag name to it.
You can't see "specificity" in a sense of which selector targets the fewest elements but simply what is most important.
Of course could the rules have been made even more complicated by differentiating such things like #header a or a#login. However this just would add more confusion to the whole system.
Also most likely this (c/w)ould be abused like the following: header#header a - this added a higher specificity but also could target more elements.
In my opinion this would add no further value to the system but only make it more complicated.
When writing CSS one should always try to keep the rules as short as possible for performance issues. If you need to overwrite a rule you still have the possibility to add another id or class - in addition to the normal cascading this is really more than enough.
You seem to be familiar with the concept of specificity, which is thouroughly described as part of w3 css specs. From the algorythm perspective, selector specificity values in the rule declaration are flat-weighted or non-positional. This means that #header a and a#login have the same specificity, meaning that if an element is eligible for both rules, the latter one will take precedence.
Personally, it took me much longer to come to terms with selectors having semantic specificity but no calculatory value. For instance, ul li and ul>li have the same weight even though the latter "feels" more specific!
I find that anyone with functional programming background finds it easier to compare specificity as four-byte values (this is in fact close to how it's implemented in major browsers - consequently overflowing the value when 256+ selectors of the same weight are used :)
It's just down to specificity - be more specific and it will work for you:
header a#login {
color: #00F; /* Blue */
}
OP, perhaps you could think of it that CSS processes the first argument (#header, and #login) first, and only after that, then it processes the second argument (a in "#header a").
So on the first process, it's made red, and then blue, but on the second process, it's overwritten to red, due to the "a" in the second argument.
All it takes to fix this is changing #login to a#login letting the DOM know this command is specific to a link.
The #header a is more specific than just #login because it's pointing at a specific element in the DOM, not just a random id.
Related
So.. I have this code:
<div id="slider">
<div class="current"><img id="img1" src="http://i.imgur.com/gWGqZly.png" /></div>
<div><img id="img2" src="http://i.imgur.com/mC1FD81.png" /></div>
<div><img id="img3" src="http://i.imgur.com/HFx9mqa.png" /></div>
</div>
As you can see the first div have a class named "current" and that's the div that i want to select. The divs are positioned on top of eachother with position: absolute;
My CSS:
#slider div {
position:absolute;
z-index: 0;
}
#slider div.previous {
z-index: 1;
}
#slider div.current {
z-index: 2;
}
I'm trying to give the first div, the one with class "current" a z-index of "2".
The selector i use for doing this is:
.current {
z-index: 2;
}
But that doesnt seem to work, that way the image wont appear on the top.
But if i instead write the selector this way:
#slider div.current {
z-index: 2;
}
Now it works.
And im a bit confused by this, doesnt those two selectors basically work the same way? What's the difference between them in this case?
Made a jsfiddle out of this https://jsfiddle.net/x1L4tfw4/5/ If you remove the "#slider div" part from the css selector you will see the difference.
You haven't stated that you have the #slider div selector in your CSS as-well.
This overrides the .current selector because its more specific.
This is a specificity issue. #slider div has a specificity of 101. #.current has a specificity of of 10.
#slider div.current comes in at 111.
The selector with the highest specificity is the one used. Now, how did I get those numbers?
The CSS standard says that you add numbers with an infinitely large base together to get it. In practice, you can think of it as being digits.
Tag names are worth one point.
Class names or attribute values are worth ten* points.
ID names are worth 100 points.
(and !important things are worth 1000 by the way).
So you add them up and see which has the highest number. That's the rule that gets applied. If two rules come with the same specificity, the one that appears last in the source code is the one that is used.
I said ten here for simplicity, but remember that the spec said infinitely large base (though browsers actually use base 256, fun fact). So ten classes do NOT equal one ID: a single ID is more specific than any number of classes (in theory).
The way you did the CSS is quite confusing . I Think you know that , these CSS do respect a straight forward system for ID and Class . Javascript Does care about ID . And Browser has their specific advantages for ID's . But CSS doesn't care about ID and class. Not until you pull this type of confusion .
Never use #id element .class in your stylesheet if you have more than one same <element-tag> in your markup. This will ruin the style .
This is due to the CSS specificity in the selectors that you're providing (or perhaps a third party library is providing). Here is a good resource to understand how CSS specificity and inheritance works.
Summary
Here is the key part from the linked article relating to how the different CSS selectors are related:
Element, Pseudo Element: d = 1 – (0,0,0,1)
Class, Pseudo class, Attribute: c = 1 – (0,0,1,0)
Id: b = 1 – (0,1,0,0)
Inline Style: a = 1 – (1,0,0,0)
I've included their examples below to help understand how this works:
p: 1 element – (0,0,0,1)
div: 1 element – (0,0,0,1)
#sidebar: 1 id – (0,1,0,0)
div#sidebar: 1 element, 1 id – (0,1,0,1)
div#sidebar p: 2 elements, 1 id – (0,1,0,2)
div#sidebar p.bio: 2 elements, 1 class, 1 id – (0,1,1,2)
Your Scenario
Now for your particular case. The first selector you use is .current which according to the information above has a specificity of:
.current (0,0,1,0)
As #Admir Geri noted in his answer, you also have a selector #slider div which has a specificity of:
#slider div (0,1,0,1)
Since the specificity of your second selector outweights that of the first, the second takes precedence and therefore you don't see your changes.
Your last selector #slider div.current has the following CSS specificity:
#slider div.current (0,1,1,1)
Since this score outweights that of any other selector. Your changes will be displayed when using this selector which is why you see them on the screen.
I have a situation in which I load a style with a selector that should be prioritized over another.
The situation looks like the one in this fiddle, in which a specific id selector is not being prioritized over another one that uses a class that is under a specific id.
--HTML
<div id="cont">
<p class="hello" id="hello">I wish I was blue</p>
</div>
--CSS
#hello {
color:blue;
}
#cont .hello {
color:red;
}
Result is red text
I'm pretty sure this could be possible without using !important - which I really would like to avoid since this will be maintained by designers with no css skills for A/B testing. I want to make a selector for them that they will only edit it's properties.
Edit: To be clear, the #hello selector is injected to the page and I want to change it to one that actually works, but I don't want to change the other selector for that purpose. Of course if I have no choice I will, but it seems reasonable to be that this css is valid as it is and overriding that selector should be possible without modifying it.
Simply use the :not selector to exclude the #hello element.
Change the first to:
#cont .hello:not(#hello) {
color:red;
}
Demo Fiddle
More on :not from MDN
The negation CSS pseudo-class, :not(X), is a functional notation
taking a simple selector X as an argument. It matches an element that
is not represented by the argument. X must not contain another
negation selector, or any pseudo-elements.
Alternatively- per the comments below, you can increase the specificity of the second selector whilst providing variations for various contexts:
#hello, #cont #hello, #hello.hello {
color:blue;
}
Demo Fiddle
I suggest you to add another id selector to the first set of CSS rules.
#cont #hello {
color:blue;
}
#cont .hello {
color:red;
}
DEMO http://jsfiddle.net/a_incarnati/53q74jah/
In this case the color was overridden in red because you were using just one id selector #hello and that it's less specific than a selector with 2 ids combined or one id and one class combined, like you have done:
#cont .hello {
color:blue;
}
One of the things to take into account when writing CSS code, it’s the concept of CSS specificity. Understanding well this concept will avoid you to have to use !important;
As Mozilla Developer Network defines it, specificity is nonetheless:
Specificity is the means by which a browser decides which property
values are the most relevant to an element and gets to be applied.
Specificity is only based on the matching rules which are composed of
selectors of different sorts.
The following list of selectors is by increasing specificity:
Universal selectors
Type selectors
Class selectors
Attributes selectors
Pseudo-classes
ID selectors
Inline style
You can measure specificity counting how many selectors are present in a CSS statement.
CSS Specificity can be represented by 4 columns of priority:
inline=1|0|0|0
id=0|1|0|0
class=0|0|1|0
element=0|0|0|1
Left to right, the highest number takes priority.
You don't need two different selectors. You can keep one:
.hello {
color:red;
}
#cont .hello {
color:blue;
}
http://jsfiddle.net/vkftfj2n/4/
Consider the following HTML markup:
<input id="foo" class="bar" name="baz">
Are the following selectors equal (or even valid):
CSS
input#foo.bar[name=baz] { }
input.bar#foo[name=baz] { }
input[name=baz].bar#foo { }
/* etc */
And is it possible to move the element name to, say, end?
Edit: I know what specificity is, I want to know in which order the tag, id, class and attributes need to be specified.
They are all valid, as they comply with the syntax of sequence of simple selectors. They are equivalent, since their meaning, including specificity, are defined in a manner that does not depend on the order of the components.
It is not possible to move the element name (type selector) to the end, for purely syntactic reasons. The spec says that a simple selector “always begins with a type selector or a universal selector. No other type selector or universal selector is allowed in the sequence”. This is to be interpreted so that the type selector, if present, must appear first. This is natural since there would be no way to distinguish it from e.g. a preceding class selector (a space could not be used since it has a quite special meaning in CSS selector syntax: .bar input is a valid selector and means something quite different from input.bar).
Please refer the answer of #Jukka as OP seemed to have changed the meaning of the question by minor edit, but if anyone's interested in specificity question before edit, than please read ahead.
First of all, neither of the selectors make sense, to be true, they are over specific.
Your selector holds an id which will be unique, so defining class as well as attr=val is not required
(If you are not using the same id for other element in some OTHER document..)
If for some case, you need them, say to override, like... (makes sense)
input#foo.bar[name=baz] {
/* More specificity overrides the selector below */
}
input[name=baz] {
/* Styles here */
}
Are the following selectors equal - YES, they are equal as far as the specficity goes, they all return a score of 121
Credits
(or even valid) - Completely Valid
Does order of tag(Not relevant), id, class - NO, whatever the order of attributes are, it doesn't matter.
BUT
The order of your CSS declaration block in the stylesheet matters, the last selector will override common properties as all the three selectors have equal specificity.
Demo (All three will render green text, regardless of the order of their attributes, but if you shuffle the CSS selectors block, the last one will override the common properties of previous two selectors - unless you define !important in one of the selector properties)
And is it possible to move the element name(Attribute) to, say, end? - YES
Pros & Cons —
All the selectors are overspecific
Bad as far as performance goes
Using attr=val selector, you are assuming that the value of the name attribute won't change, if it does, you will have to change your selectors as well.
P.S : Have an habit of quoting the attribute values.
Those are all legal:
<input type-"text" id="foo" class="bar" name="baz">
input#foo.bar[name=baz] { border:1px solid blue; }
input.bar#foo[name=baz] { border:1px solid red; }
input[name=baz].bar#foo { border:1px solid green; }
http://jsfiddle.net/hGj5B/
Remove the various style blocks and note that each selector will select the textbox.
By "equal", if you are asking is they have equivalent specificity, then the answer is yes given each selector has the same amount of elements, classes, attribute selectors, and ids. Since they are all equal, the order of the blocks in your stylesheet will serve to determine which conflicting styles will win out.
You cannot move the element to the end, as the other segments of the selector describe it by coming after.
Yes all of them are legal , But while execution the Later one Will over ride the Earlier Declarations,but some exceptions are there
check the Flow exceptions Here
input[name=baz].bar#foo { border:1px solid green; }
input.bar#foo[name=baz] { border:1px solid red; }
input#foo.bar[name=baz] { border:1px solid blue; }
input { border:1px solid #000000; }
http://jsfiddle.net/hGj5B/
for More Details Refer this Question..
The sequence of execution of CSS
Let's say I have the following HTML:
<span id="id1" class="class1 class2">This is a test</span>
and if #id1, .class1 and .class2 all have different sets of mutually exclusive CSS rules, which one wins? I have been testing an example and in one case it's choosing (I think) the one that is listed at the bottom of the CSS file, but in another case it seems non-deterministic.
Is there a specific rule in this case?
The basic principle of cascading in CSS is that you have one element, and one or more CSS rules that apply to the same element (because the element matches their selectors). In this process, all applicable styles are computed, with any conflicts resolved (or cascaded), and then, well, applied.
If the rules and their declarations are mutually exclusive, then none of them "wins" over any of the others per se, since there's no conflict to resolve and therefore nothing to override. For example, if you have these rules:
#id1 {
color: red;
}
.class1 {
border-width: 1px;
}
.class2 {
border-style: dashed;
}
Then your element will have red text and a dashed red border that's 1 pixel thick. There are no conflicts, so all of them will combine in effect. (Note that the border is red due to special behavior.)
jsFiddle preview
It's only when you have the same property declared in more than one rule that selector specificity and cascading become relevant, because then you'd need to override values for that same property. In that case, then as already mentioned IDs take precedence over classes and equally-specific rules are applied from the top down; read about selector specificity.
For example, if you have these rules:
#id1 {
color: red;
}
.class1 {
text-decoration: underline;
color: green;
}
.class2 {
text-decoration: none;
color: blue;
}
Then your element will have red text with no decoration, because
the color value in #id1 overrides that in both classes, and
the text-decoration value in .class2 overrides that in .class1.
jsFiddle preview
Remember that all this has to apply to the same element. If you have a parent that only has an ID, with a child that only has a class, then none of this will apply because you're dealing with entirely separate elements. What comes into play instead is inheritance, which is also covered in the document I link to above.
CSS reads up to down, so class2 will win!
More Info
http://css-tricks.com/specifics-on-css-specificity/
ID will take precedence over class.
If an element has same styles defined multiple times using ID, the latter will take precedence over the former except the case that you're using !important
The order of precedence with CSS is as follows:
1. !important
2. Inline styles which defined inside an HTML element
3. Internal styles which defined in the head section
4. External stylesheet which is a link to a sheet (<link rel="stylesheet" type="text/css" href="style.css" />)
5. Browser default
This is easy - the one that is closer and more refined win (just like life)
I.e.
Got a blank sheet then:
Start off with class - apply those (aka class1, class2)
But you know about that individual (id)
And then apply that..
So (if there is a "winner") the id wins
Unless the tag has style in its attributes - That would win
With this HTML code.
<div class="noote">
<p class="first admonition-title">Noote</p>
<p class="last">Let's noote.</p>
</div>
How can I set the color of Noote to be red with css?
I mean, how can I set something for (div class="noote") and (p class="first") under it with css?
Try this:
/*this will apply for the element with class first
inside the element with class noot */
.noote .first{
color:red;
}
/* If you wanted to apply a rule for both individually
you can do: */
.noote, .first{
border:1px solid red;
}
div.note{
...
}
Refers to the div element that has the class note.
p.first{
...
}
Refers to the p element that has the class first.
div.note p.first{
...
}
Refers to the p element inside note that has the class first.
In addition, if you want to set an element child without setting a class to it,
div.note p:first-child{
/* it refers to the first p that contains noote */
}
#amosrivera's got it.
It's worth nooting that descendant selectors require more CPU. I always use more specific rules where possible. So instead of
.noote .first{
backgorund:red;
}
You could say
.noote > .first{
backgorund:red;
}
A nominal difference in most cases, but still a good habit.
Really?
Descendant selectors are
inefficient... The less specific the
key, the greater the number of nodes
that need to be evaluated.
— Google "Let's make the web
faster" docs
And
Descendent selectors are a major slow
down to the Safari browser
— John Sykes, May 2008
Some performance tests show little impact, and most writers agree that it only makes a difference on very large documents.
But mainly, I'm just going with my programmer instinct — say what you mean, and no more.