With the LESS preprocessor, you can nest CSS code inside other CSS code, like this:
.Element {
.AnotherElement {
background-color: #FFF;
}
.YetAnotherElement {
background-color: #000;
}
}
This would make the background of .Element .AnotherElement white, and it makes .Element .YetAnotherElement have a background color of black. It does it all without writing it out like:
.Element .AnotherElement {
background-color: #FFF;
}
.Element .YetAnotherElement {
background-color: #000;
}
Does the first example coincide with CSS syntax, or do I have to use the LESS preprocessor?
Nesting is a feature of LESS and SASS, not native to CSS.
This is one of the most common uses for CSS preprocessors, but they offer a lot more too.
No, css doesn't support this syntax, in your css example the "Element" and "AnotherElement" will to receive this properties, AnotherElement will not inherit properties of Element.
Related
Are there any tools to compile CSS custom properties declared at not :root rule? I want following code with custom properties
.dark {
--bg-color: black;
--fg-color: white;
}
.light {
--bg-color: white;
--fg-color: black;
}
.foo {
background: var(--bg-color);
display: block;
}
.bar {
color: var(--fg-color);
display: inline;
}
be compiled to their non-custom-prop equivalents like that
.light .foo, .light.foo {
background: white;
}
.dark .foo, .dark.foo {
background: black;
}
.light .bar, .light.bar {
color: black;
}
.dark .bar, .dark.bar {
color: white;
}
.foo {
display: block;
}
.bar {
display: inline;
}
The goal is to
switch color schemes by switching dark/light class on root DOM element
use valid css syntax (no sass less)
keep rules code compact
It's actually not safe to do that. I can tell you because I tried so hard to make a safe transformation.
But I failed.
https://github.com/postcss/postcss-custom-properties/issues/1
Ideal solution. Your example is valid CSS and can be used in many browsers (not in IE, Edge (but is in development) and Opera Mini as of writing this answer, 2017-03-27, other major browsers are fine).
Suboptimal solution. Some CSS can be transpiled to achieve better browser support. The solution I found does not support variables on non-:root elements, however. There are also other objections against transpiling of 'future' CSS into 'current' CSS. To the best of my knowledge, you will have to implement your own transpiler (or postcss plugin) if you want to transpile custom properties not on the :root element, but be warned that that is hard in general. Now you don't need the general part, so it is possible. Just does, to the best of my knowledge, not exist yet.
Preprocessing solution. Of course, you don't need a general implementation of custom properties. You have different themes that have their own values for the same set of properties and that's it. Thus, a separate stylesheet can be created as a preprocessing step using any CSS preprocessor.
Now you say the following,
use valid css syntax (no sass less)
but I am going to show this anyway, because I believe that it is a valid solution to your problem. It is definitely the only one I know that actually works if you want to/need to support IE, Edge and/or older versions of other major browsers (Firefox < 31, Chrome < 49, Safari < 9.1, Opera < 36)
You could do this using SASS for example, to do the transpiling on the server side.
// define styles, use variables throughout them
// your entire style definition goes into this mixin
#mixin myStyles($fg-color, $bg-color) {
.foo {
display: block;
background: $bg-color;
}
.bar {
display: inline;
color: $fg-color;
}
}
// define themes, that set variables for the above styles
// use named arguments for clarity
.dark {
#include myStyles(
$fg-color: white,
$bg-color: black
);
}
.light {
#include myStyles(
$fg-color: black,
$bg-color: white
);
}
This compiles to the following.
.dark .foo {
display: block;
background: black;
}
.dark .bar {
display: inline;
color: white;
}
.light .foo {
display: block;
background: white;
}
.light .bar {
display: inline;
color: black;
}
This is not exactly what you want to obtain, but very close. Realistically, I think this is the closest you will get to obtaining your desired output. I know you want to
keep rules code compact
but what you are saying there (I think) is that you want to split out custom properties from their rules to save on number of rules, which is not something any preprocessor I know supports.
You can organize your source SASS in separate files to keep an overview easily. You can even set up a build system that generates a separate stylesheet for every theme you have. It is then possible to have your users select an alternative stylesheet. Browsers have some support for this, but switching using JavaScript is also definitely possible in the latter case. Simply set all stylesheets to be disabled except for the selected one. Here is an example.
I'm using the SASS port of Bootstrap, and I'm wondering if there's any difference between using the pre-defined mixins and using SASS's #extend.
For instance, if I have:
<div class="wrapper">
Some content here....
</div>
Is there any difference between doing
.wrapper {
#include make-row();
}
and
.wrapper {
#extend .row;
}
?
If there's no difference, are there other mixins that aren't equivalent to a single #extend statement? If there aren't such mixins, why do the mixins even exist?
The big difference between #extend and a mixin is the way the css is compiled. It doesn't look like much in simple examples, but the differences and implications are significant and can be a real headache in the wild if used carelessly. #extend is a little bit like fools gold, looks great at first, but ...
Let's look at a simple example:
#extend
.row {
width: 50px;
}
.new-row {
#extend .row;
}
.another-row {
#extend .row;
}
compiles into:
.row,
.new-row,
.another-row {
width: 50px;
}
mixin
#mixin row() {
width: 50px;
}
.new-row {
#include row();
}
.another-row {
#include row();
}
compiles into:
.new-row {
width: 50px;
}
.another-row {
width: 50px;
}
A mixin includes the properties everywhere it is hit - copying them each time - whereas an #extend groups the selectors and defines the properties once. This isn't immediately obvious, because the difference is in the compiled css but it has some important implications:
Load order
With #extend the selectors will be grouped at the first point in the sass where they are encountered which can lead to some weird over-riding. If you define a selector and use #extend to bring in a property to and try to override a property defined earlier in your sass, but after the point at which the extended properties are grouped in the css then the override will not work. This can be quite perplexing.
Consider this logically ordered set of css definitions and the likely HTML: <div class='row highlight-row'></div>:
.red-text {
color: red;
}
.row {
color: green;
}
.highlight-row {
#extend .red-text;
}
compiles into:
.red-text,
.highlight-row {
color: red;
}
.row {
color: green;
}
So even though the sass ordering makes it look like the row colour would be red, the compiled css will make it green
Poor groupings
#extend can result in poorly grouped selectors in the resulting css. You can end up with thirty or forty unrelated things all sharing the same property for example. Using #extend for fonts is a good example of this.
Nesting
If you are using deeply nested sass (which is not good, btw) and you use #extend you will duplicate the fully nested selector for every #extend you use, resulting in bloated css. I've seen this a lot:
.selector-1 .selector-2 .selector-3 .selector-4,
.selector-1 .selector-2 .selector-3 .selector-4 a,
.selector-1 .selector-2 .selector-3 .selector-4 li,
.selector-1 .selector-2 .selector-3 .selector-4 td {
font-family: arial;
}
If you're new to SASS it pays to look at the compiled css.
Media queries
#extend do not work inside media queries, because media queries are not selectors.
Conclusion
My rule of thumb is to use an #extend over a mixin if you have no parameters and if you can reasonably define the #extend and share it amongst a few tightly related selectors that exist nearby in the sass, for example, in the same file that defines a sass module. Buttons are a good example of well used #extend:
%button {
padding: 10px;
}
.call-to-action {
#extend %button;
background-color: $green;
}
.submit {
#extend %button;
background-color: $grey;
}
The best article to help make the choice is here
PS, the % sign is a use of placeholder extends
Can CSS have inheritance like OOP?
For example I have this style
.myButton {
background-color:#ffec64;
border:1px solid #ffaa22;
}
Can I define parent for color attributes? Something like
myYellow: #ffec64
So that in every styles I will just use
.myButton {
background-color:myYellow;
border:1px solid #ffaa22;
}
So that changing yellow color will only be on myYellow attribute not for every background-color attributes.
Thanks in advance
This is not possible when using CSS alone.
You can do this by using a css preprocessor like LESS or SASS. These allow for variables, mixins, functions and many other techniques that allow you to make CSS that is more maintainable, themable and extendable.
Once you have written your LESS or SASS you then need to compile it to standard css (in the case of LESS this can be done client-side).
You may need to use CSS Pre Processors like LESS or SASS.
Example Using LESS variables
#myYellow: #ffec64;
.myButton {
background-color: #myYellow;
border: 1px solid #ffaa22;
}
or even you can use LESS mixin to inherit css class.
.myCommonButton {
background-color: #myYellow;
border: 1px solid #ffaa22;
}
.myButton {
.myCommonButton;
color: black;
}
I've tried to find the answer, and can't seem to do so, which is leading me to believe that it isn't possible. With my minimal knowledge of how CSS works, I also don't think it would be possible, but I just want to ask before I start working around a problem that may or may not exist.
Basically what I'm trying to do is use a previously defined attribute in a new class in my CSS stylesheet. For instance, say I had a couple of classes that just held background or font colors, like this:
.black { background-color: #000000; color: #000000; }
.white { background-color: #FFFFFF; color: #FFFFFF; }
Now if I was defining a new class (or using any selector for that matter), would it be possible to use the value of an attribute from an already existing class? Here is what my idea would look like:
.newClass {
width: 100%;
height: 100%;
background-color: .black; /* this would just get the background-color attribute from the .black class definition */
}
background-color: .black; is basically just a placeholder for "get the background-color attribute from the .black class definition". Is that possible using purely CSS? I'm aware of a ton of alternatives with PHP/JS, but I'd like to know if CSS can tackle this by itself. Thanks guys.
SASS is a thing to go. Your code will be like
#mixin black-theme {
.black { background-color: #000000; color: #000000; }
}
.newClass {
width: 100%;
height: 100%;
#include black-theme;
}
SASS
PHP compiler for SASS PHPSASS
There are javascript based solutions too like LESS but I generally don't recommend them as if Javascript load slow then presentation becomes jerky.
No, this is not currently possible in CSS. CSS does not have variables or the ability to reference values from previous rules. You would have to look for a CSS preprocessing language that gets processed into plain CSS before going onto the web site.
If you're willing to go the preprocessed way, you can look at SASS or LESS.
Yea possible using SASS or LESS css
#bgcolor : black;
.newClass {
width: 100%;
height: 100%;
background-color:#bgcolor;
}
I have defined some background colors that I'll be using on my site. So I can easily set the background color of different elements like:
.background_highlite{
background-color: rgb(231, 222, 207); /*Cream in my Coffee*/
}
.background_shadow{
background-color: rgb(201, 179, 156); /*Moose Mousse*/
}
Now, if I want all textarea elements on my page to have Moose Mousse color as their background I want to write another CSS rule that references back to .background_shadow, so I only have to change the rgb values in one place.
Something like:
textarea{
height:50px;
background-color: background_highlite /* want to feed forward to keep the rgb in one place */
}
Is this possible with CSS?
People have been frustrated by CSS's simplistic structure, and have created pre-processors to write CSS more conveniently. Look at Less, for example, or CleverCSS.
You can assign all the elements the same class, and then set the background color in the class's CSS:
<textarea class="background_shadow">blah</textarea>
Keep in mind that you can assign a number of classes to any element, so you can use one class just to control the background color, and then use other classes for your other needs:
<textarea class="background_shadow another_class something_else">...</textarea>
Not really. http://dorward.me.uk/www/css/inheritance/ lists your main options.
Sorry, no. CSS does not support variables, or chaining.
however, there is a javascript library that allows that. http://lesscss.org/
The best you can do would be
.hilight textbox {
background: black;
}
textbox {
color: pink;
}
.background_shadow {
background: grey;
}
Or, of course, you could add the .hilite class to your div.
You have two options to work with:
Native CSS, which is possible, but not good to maintain.
Preprocessor, like xCSS, which can create more cleaner code and provide variables.
For simple projects I assume, native CSS will be good. But in more complicated it`s best to use some sort of processors, like pals talked earlier.
In this method you can always use some human readable rule like:
.blabla {min-height: 20px}, which pre-processor by your own logic transform to CSS, that all of our target browsers can understand, like .blabla {min-height: 20px; height: auto !important; height: 20px;} etc.
Also what I realy like in preprocessors is that you can right code, as here:
.specialClass extends .basicClass {} // see more at extends
.selector {
a {
display: block;
}
strong {
color: blue;
}
} // see more at children
or what you needed is vars {
$path = ../img/tmpl1/png;
$color1 = #FF00FF;
$border = border-top: 1px solid $color1;
} // see more at vars