I've read several tutorials on CSS, but none of the sites I've looked at mentions or explains what a "." means in CSS.
What does the . mean?
Nothing without context.
I'll hazard a guess that you are referring to a class selector.
Well, in the following context:
.foo {
//properties
}
it indicates that foo is a class. A # means it's an id and if it has nothing it means that it is for all tags of that type. So, in html, you would implement something with a "." like this:
<div class = "foo"></div>
For a "#" it would be
<div id = "foo"></div>
Use class/"." if you want to apply it to more than one thing. Use id/"#" if you want it to apply to one thing.
Ok, so if your wondering what a class is:
A class is one of the three (I think it's 3) types of ways you select stuff in css. The id (which I explained) says that the following properties apply to anything (usually one thing) with 'id="foo"' in its tag. A class selector means that it applies to everything with a "class="foo"" in its tag. If it has none of these than it means that it applies to all things with that name.
.foo { //applies to all things with "class="foo"" in tag.
border: black thin solid // applies a black border to them.
}
#foo { //applies to all things with "id="foo"" in tag.
border: black thin solid // applies a black border to them.
}
div{ //applies to all div tags.
border: black thin solid // applies a black border to them.
}
h1{ //applies to all h1 tags
border: black thin solid // applies a black border to them.
}
It is a class selector. Means the rule should be applied to all elements that have an attribute class with the value after the ..
Related
how do you apply a specific css to second-page
HTML
<div className = "section-header second-page">SOME MESSAGE</div>
Assuming the above:
CSS
.section-header {
background-color: black,
}
i want to apply a different background color specifically to second-page that does not modify section-header.
If you want the styling to apply to any element with .second-page class you should use:
.second-page {
backgound-color: red,
}
If you want the styling to apply only to .section-header elements that also have .second-page class, then you should use:
.section-header.second-page {
backgound-color: red,
}
When there's no space between two classes, it means it refers to an element with both classes.
For more information on CSS selectors, please check
https://www.w3schools.com/cssref/css_selectors.asp
Your HTML should be:
<div class="section-header second-page">SOME MESSAGE</div>
Your CSS could be:
.second-page {
background-color: black,
}
You can mix multiple classes within the HTML or target them separately.
If you need to validate your HTML code you can use this free service:
https://validator.w3.org/#validate_by_input
I know CSS selector with the highest specificity takes precedence (i.e. .classname < #idname).
I also know that if things are the same specificity, then the last statement called takes precedence:
.classname1 { color: red; }
.classname1 { color: blue; } // classname1 color will be blue
Does the ordering of HTML classes on a DOM element affect the statement priority?
I have to disagree slightly with Jon and Watson's answers, as...
Yes, it Can (depending on the statement)
Your question is:
Does the ordering of CSS classes on a DOM element affect the statement priority?
Which does depend on the statement in question.
HTML Ordering Does Not Typically Matter
The following are equivalent when it comes to a straight call to a class (i.e. .class1 or .class2) or to a combined call (i.e. .class1.class2 or .class2.class1):
<div class="class1 class2"></div>
<div class="class2 class1"></div>
Cases Where Statement Priority for above HTML Can be Affected Based on HTML Order
The main place where ordering in HTML matters is with the use of attribute selectors in your CSS.
Example 1 Fiddle using the following code seeking to match attribute value will NOT have any change in font color, and each div will have different properties because of the ordering of the classes:
[class="class1"] {
color: red;
}
[class="class1 class2"] {
background-color: yellow;
}
[class="class2 class1"] {
border: 1px solid blue;
}
Example 2 Fiddle using the following code seeking to match beginning of attribute value will NOT have any change in font color for the second div, and each div will have different properties because of the ordering of the classes:
[class^="class1"] {
color: red;
}
[class^="class1 class2"] {
background-color: yellow;
}
[class^="class2 class1"] {
border: 1px solid blue;
}
Example 3 Fiddle using the following code seeking to match end of attribute value will NOT have any change in font color for the first div, and each div will have different properties because of the ordering of the classes:
[class$="class1"] {
color: red;
}
[class$="class1 class2"] {
background-color: yellow;
}
[class$="class2 class1"] {
border: 1px solid blue;
}
A Clarifying Statement about "Priority"
To be clear, in the cases above, what is affected as far as "statement priority" is concerned is really a matter of whether the statement actually applies or not to the element. But since the application or not is in a sense, the basic priority, and since the above are cases where such application is actually based on the ordering of the classes on the HTML Dom element (rather than the presence or absence of the class), I thought it worth adding this as an answer.
Possible Valid Use of Class Ordering?
This is a thought occurring to me, based on BoltClock's comment. Consider just two classes being used to style elements based on whatever factors are deemed critical to different styling. These two classes theoretically can replace the use of eleven different individual classes using the combination of attribute selectors (actually, as will be noted later, the possibilities are almost limitless with but a single class, but I'll discuss that in a moment since this post is about ordering of multiple classes). For these two classes we can style elements differently as follows:
Assuming these HTML Combinations
<div class="class1">Element 1</div>
<div class="class2">Element 2</div>
<div class="class1 class2">Element 3</div>
<div class="class2 class1">Element 4</div>
CSS Possibilities
/* simply has the class */
.class1 {} /* affects elements 1, 3, 4 */
.class2 {} /* affects elements 2-4 */
/* has only a single class */
[class="class1"] {} /* affects element 1 only */
[class="class2"] {} /* affects element 2 only */
/* simply has both classes */
.class1.class2 {} /* affects elements 3-4 */
/* has both classes, but in a particular order */
[class="class1 class2"] {} /* affects element 3 only */
[class="class2 class1"] {} /* affects element 4 only */
/* begins with a class */
[class^="class1"] {} /* affects elements 1 & 3 only */
[class^="class2"] {} /* affects elements 2 & 4 only */
/* ends with a class
NOTE: that with only two classes, this is the reverse of the above and is somewhat
superfluous; however, if a third class is introduced, then the beginning and ending
class combinations become more relevant.
*/
[class$="class1"] {} /* affects elements 2 & 4 only */
[class$="class2"] {} /* affects elements 1 & 3 only */
If I calculate right, 3 classes could give at least 40 combinations of selector options.
To clarify my note about "limitless" possibilities, given the right logic, a single class can potentially have imbedded in it code combinations that are looked for via the [attr*=value] syntax.
Is all this too complex to manage? Possibly. That may depend on the logic of exactly how it is implemented. The point I am trying to bring out is that it is possible with CSS3 to have ordering of classes be significant if one desired it and planned for it, and it might not be horribly wrong to be utilizing the power of CSS in that way.
No, it does not. The relevant part of the W3C standard makes no mention of the order of appearance for classes.
No, it does not, like you said, if two rules have the same specificity, the one that comes later in your CSS will be applied.
No. But if you want to make one of your declaration blocks to has more precedence (w/o many !importants) make its selector more specific.
For example, for a div:
div.classname1 { color: red; } /* classname1 color will be red (for `div`s) */
.classname1 { color: blue; }
What's missing or a little hard to find in other answers is this:
What matters is the order in which the browser reads/parses the class names
The class defined last will win
.a {
color: red;
}
.b {
color: blue;
}
<div class="a b">This text will be blue</div>
<div class="b a">This text will ALSO be blue</div>
Example comes from this source
May be affected by the order of your imports
Because if this you may need to pay attention to how you import CSS in your files.
For example in my JavaScript based project I have a component that I can pass extra classes to. In order for my own classes to overwrite styles of the classes of the component itself I need to first import the component I wish to style (which will import its own styles) and only then import my own styles:
//import the component first, which will import css
import {SomeComponent} from 'some-library/SomeComponent';
//And THEN our own styles
import './styles.css';
return <SomeComponent className={myClassName} />
Like this my buildprocess (Webpack) will put my own classes later in the CSS bundle than the components ones.
I'm looking into LESS because I definitely see some of their benefits. For instance colour declaration.
One thing I don't understand tho, and maybe I'm not getting the flow right is - why use the following LESS snippet
.radius {
-webkit-border-radius:5px;
-moz-border-radius:5px;
border-radius:5px;
}
.btn-red{
background-color:red;
.radius;
}
.btn-green{
background-color:green;
.radius;
}
...
When we can use the .radius class in the html file right away. I'm left with the impression that LESS will add a ton of duplicate code once it gets compiled.
I'm using the following, which makes more sense. Same with font-size, margins, etc... Aren't classes used in such cases?
<div class="btn-red radius">Cancel</div>
<div class="btn-green radius">Go</div>
The snippet above does not benefit from SASS/LESS capabilities that much. Lets have a closer look and check this SCSS snippet.
// Abstract placeholder.
%radius {
border-radius: 5px;
}
// Put your global styling here.
// I'm assuming that you can alter the markup and have button.btn.btn-green
.btn {
// Color modifier.
&-red {
#extend %radius;
background-color: red;
}
&-green {
#extend %radius;
background-color: green;
}
}
The CSS output will be:
.btn-red, .btn-green {
border-radius: 5px;
}
.btn-red {
background-color: red;
}
.btn-green {
background-color: green;
}
And then you have to pick up Autoprefixer and vendor-prefixes issue is solved once and for all.
Because now, you can just specify the class btn_red or btn_green and all the buttons will automatically have a radius.
Your HTML should contain only the semantics, and styling or classes referring to styling should not be part of it.
That applies to the other classes as well. If for instance, you would rename btn_red to btn_cancel, you have a meaningful classname that you can apply to any kind of cancel button. And in the CSS you can specify that a cancel button is red and a 'Go' button is green, and both have a radius, without needing to modify the HTML at all.
So, the ultimate goal is to have the HTML describe the structure and the CSS describe how that structure should look. And a CSS preprocessor is only their to make a bulky spaghetti-like CSS file more structured.
There are several benefits.
You can use more semantic class names. Rather than encoding style information directly in your class names, (btn-red, radius) you could use a single class that conveys the usage of the style, rather than its contents.
You can avoid repeating yourself.
#radius-size: 5px;
-webkit-border-radius:#radius-size;
-moz-border-radius:#radius-size;
border-radius:#radius-size;
You can parameterize it so that you'd be able to use different radiuses (radii?) in different contexts.
.radius(#radius-size) { ... }
Because there are cases that developer has-no-access or don't-want to change the markup. and the only solution is to include all props from a predefined class.
for example:
you have bootstrap loaded (then you already have .has-success and .has-error classes) and if you want to use HTML5's native form validation using input's :valid and :invalid states, you have to use JavaScript to add/remove success/error classes based on input's states. but with this feature of LESS you can include all props of success/error class inside input's states. the code for this example could be something like this:
#myinput {
&:valid { .has-success; }
&:invalid { .has-error; }
}
I know CSS selector with the highest specificity takes precedence (i.e. .classname < #idname).
I also know that if things are the same specificity, then the last statement called takes precedence:
.classname1 { color: red; }
.classname1 { color: blue; } // classname1 color will be blue
Does the ordering of HTML classes on a DOM element affect the statement priority?
I have to disagree slightly with Jon and Watson's answers, as...
Yes, it Can (depending on the statement)
Your question is:
Does the ordering of CSS classes on a DOM element affect the statement priority?
Which does depend on the statement in question.
HTML Ordering Does Not Typically Matter
The following are equivalent when it comes to a straight call to a class (i.e. .class1 or .class2) or to a combined call (i.e. .class1.class2 or .class2.class1):
<div class="class1 class2"></div>
<div class="class2 class1"></div>
Cases Where Statement Priority for above HTML Can be Affected Based on HTML Order
The main place where ordering in HTML matters is with the use of attribute selectors in your CSS.
Example 1 Fiddle using the following code seeking to match attribute value will NOT have any change in font color, and each div will have different properties because of the ordering of the classes:
[class="class1"] {
color: red;
}
[class="class1 class2"] {
background-color: yellow;
}
[class="class2 class1"] {
border: 1px solid blue;
}
Example 2 Fiddle using the following code seeking to match beginning of attribute value will NOT have any change in font color for the second div, and each div will have different properties because of the ordering of the classes:
[class^="class1"] {
color: red;
}
[class^="class1 class2"] {
background-color: yellow;
}
[class^="class2 class1"] {
border: 1px solid blue;
}
Example 3 Fiddle using the following code seeking to match end of attribute value will NOT have any change in font color for the first div, and each div will have different properties because of the ordering of the classes:
[class$="class1"] {
color: red;
}
[class$="class1 class2"] {
background-color: yellow;
}
[class$="class2 class1"] {
border: 1px solid blue;
}
A Clarifying Statement about "Priority"
To be clear, in the cases above, what is affected as far as "statement priority" is concerned is really a matter of whether the statement actually applies or not to the element. But since the application or not is in a sense, the basic priority, and since the above are cases where such application is actually based on the ordering of the classes on the HTML Dom element (rather than the presence or absence of the class), I thought it worth adding this as an answer.
Possible Valid Use of Class Ordering?
This is a thought occurring to me, based on BoltClock's comment. Consider just two classes being used to style elements based on whatever factors are deemed critical to different styling. These two classes theoretically can replace the use of eleven different individual classes using the combination of attribute selectors (actually, as will be noted later, the possibilities are almost limitless with but a single class, but I'll discuss that in a moment since this post is about ordering of multiple classes). For these two classes we can style elements differently as follows:
Assuming these HTML Combinations
<div class="class1">Element 1</div>
<div class="class2">Element 2</div>
<div class="class1 class2">Element 3</div>
<div class="class2 class1">Element 4</div>
CSS Possibilities
/* simply has the class */
.class1 {} /* affects elements 1, 3, 4 */
.class2 {} /* affects elements 2-4 */
/* has only a single class */
[class="class1"] {} /* affects element 1 only */
[class="class2"] {} /* affects element 2 only */
/* simply has both classes */
.class1.class2 {} /* affects elements 3-4 */
/* has both classes, but in a particular order */
[class="class1 class2"] {} /* affects element 3 only */
[class="class2 class1"] {} /* affects element 4 only */
/* begins with a class */
[class^="class1"] {} /* affects elements 1 & 3 only */
[class^="class2"] {} /* affects elements 2 & 4 only */
/* ends with a class
NOTE: that with only two classes, this is the reverse of the above and is somewhat
superfluous; however, if a third class is introduced, then the beginning and ending
class combinations become more relevant.
*/
[class$="class1"] {} /* affects elements 2 & 4 only */
[class$="class2"] {} /* affects elements 1 & 3 only */
If I calculate right, 3 classes could give at least 40 combinations of selector options.
To clarify my note about "limitless" possibilities, given the right logic, a single class can potentially have imbedded in it code combinations that are looked for via the [attr*=value] syntax.
Is all this too complex to manage? Possibly. That may depend on the logic of exactly how it is implemented. The point I am trying to bring out is that it is possible with CSS3 to have ordering of classes be significant if one desired it and planned for it, and it might not be horribly wrong to be utilizing the power of CSS in that way.
No, it does not. The relevant part of the W3C standard makes no mention of the order of appearance for classes.
No, it does not, like you said, if two rules have the same specificity, the one that comes later in your CSS will be applied.
No. But if you want to make one of your declaration blocks to has more precedence (w/o many !importants) make its selector more specific.
For example, for a div:
div.classname1 { color: red; } /* classname1 color will be red (for `div`s) */
.classname1 { color: blue; }
What's missing or a little hard to find in other answers is this:
What matters is the order in which the browser reads/parses the class names
The class defined last will win
.a {
color: red;
}
.b {
color: blue;
}
<div class="a b">This text will be blue</div>
<div class="b a">This text will ALSO be blue</div>
Example comes from this source
May be affected by the order of your imports
Because if this you may need to pay attention to how you import CSS in your files.
For example in my JavaScript based project I have a component that I can pass extra classes to. In order for my own classes to overwrite styles of the classes of the component itself I need to first import the component I wish to style (which will import its own styles) and only then import my own styles:
//import the component first, which will import css
import {SomeComponent} from 'some-library/SomeComponent';
//And THEN our own styles
import './styles.css';
return <SomeComponent className={myClassName} />
Like this my buildprocess (Webpack) will put my own classes later in the CSS bundle than the components ones.
HTML
<div data-whatever='something cols-16 else'>
</div>
This works:
Will work - CSS
[data-whatever*='cols-1'] {
background: red;
}
It will find the div and make it red.
Will not work - CSS
[data-whatever='cols-16'] {
background: red;
}
It will not find the div because there are other stuff in there as well.
Problem
The problem with the working CSS, is that it matches both cols-16, cols-1 and any other that starts with cols-1.
Question
Is it possible to find an attribute value, exact match?
In order to target the class cols-16 (even when it appears with other classes)
and not target the cols-1 class use this:
[data-whatever~='cols-16'] {
background: green;
}
You can see this working in this fiddle.
For more info see this post (Goto #16. - X[foo~="bar"]
The tilda (~) symbol allows us to target an attribute which has a
spaced-separated list of values.
try this:
[data-whatever~='cols-1'] {
background: red;
}
It worked for me if I didn't missunderstand your question
Edit: I just remembered the ~= randomly, tried it, and pasted it.
But I just googled a bit (I had curiosity and found This, it's quite interesting)
To ensure that it only matches cols-1 and not cols-16 without relying on the cols-16 style overriding the cols-1 style (below), you could:
[data-whatever='cols-1'],
[data-whatever^='cols-1 '],
[data-whatever*='cols-1 '],
[data-whatever$='cols-1'] {
background: red;
}
This matches data-whatever="cols-1", data-whatever="... cols-1", data-whatever="cols-1 ..." or data-whatever="... cols-1 ...".
JSFiddle example.
Thanks to aleation's answer: data-whatever~="cols-1" achieves the same as the above in just one selector.
--
At any rate your cols-16 styling could overwrite your cols-1 styling anyway, depending on the order it was presented:
[data-whatever*='cols-1'] {
background: red;
}
[data-whatever*='cols-16'] {
background: blue;
}
/* cols-1 will be red. cols-16 will be blue */
JSFiddle example.