Move over Sass, we have #CSS variables! I still love Sass of course. But it’s great native CSS supports this. No need for a preprocessor & no more compiling 🥳
Global scope will allow you to access the variable everywhere. Local scope will just be within your specific selector 👍
:root {
/* 1. Defining in Global Scope */
--color: red;
/* 2. Available in all selector*/
color: var(--color); /* red */
}
.local {
/* 1. Defining in Local Scope */
--color: blue;
/* 2. Scoped to the .local class only */
color: var(--color); /* blue */
}
Story time...
It's been awhile since I had story time, so let's me share the journey of a discontent css developer who finally stopped being so angry 😂
Yucky Duplicated CSS Code
Back in the days, I remember having to make a lot of duplicate styling...
.subtitle {
color: #999;
}
.subtext {
color: #999;
}
This was always annoying to me! Because I knew the concept of variables
from other programming language. So I always cringe when I see this duplication.
Sass to the rescue 🦸♀️
And then I discovered Sass. Yay, I can finally utilize variables!
$secondary-color: #999;
.subtitle {
color: $secondary-color;
}
.subtext {
color: $secondary-color;
}
This was all great. But then you have to deal with installing Sass to your project and the overhead of dealing with a preprocessor and compiling. And for a tiny a project, the effort of setting up Sass just doesn't make sense. So back to being a complain-y developer and tweeting a firestorm of how CSS is annoying...cause that's why Twitter was created right, it's a place for angry developers to vent 😅
Out of the way Sass, CSS is my hero 💪
CSS finally had enough of me sending it bad energy. So it introduced CSS variables. Now I can set a variable natively. No preprocessor, no extra installation, just plain CSS out of the box. Beautiful isn't it 😍
:root {
--secondary-color: #999;
}
.subtitle {
color: var(--secondary-color);
}
.subtext {
color: var(--secondary-color);
}
Can I complain about the awkward syntax 🤔 Sure...but gratitude is the way to happiness. So I'm going to soak in this variable heaven for a bit...until the next story time 😂
CSS Variable Syntax
1. Declaring a CSS variable
You prefix your variable name with 2 dashes, --
.
--variable-name: some-value;
2. Using the CSS variable
And to use it. You use pass your variable name into var()
.
css-property: var(--variable-name);
Scopes in CSS Variable
You can declare your CSS variable in the global scope, meaning it can be available throughout your entire app. Or you can just set the CSS variable in the local scope, where it's only available in the specific selector.
Global Scope
To declare it in the global scope, you first set your definition inside :root {}
.
:root {
--primary-color: #000;
}
h1 {
color: var(--primary-color);
}
Local Scope
To declare it in the local scope, you just define your variable inside your element block. And that variable is only available within that selector. If you tried to use is somewhere, it won't have any effect.
h2 {
--h2-color: #999;
color: var(--h2-color);
}
h3 {
/* No Effect */
color: var(--h2-color);
}
Examples
Let's go over some different ways you can have some fun defining CSS variables ✅
You can set multiple value
:root {
--margin: 10px 20px;
}
div {
margin: var(--margin);
}
You can build up values
This is handy when used it with calc()
. Are you sensing some cool dynamic sizing application with this. Ya, my spidy senses are tingling too! 🕷
:root {
--value: 5;
}
div {
padding: calc(var(--value) * 1px); /* 5px */
}
⚠️Note: You can not concatenate a unitless value with a unit. So this won't work:
:root {
--value: 5;
}
div {
padding: var(--value) px; /* ❌ will not give you 5px */
}
☝️If you're trying to build up values, you need to use css calc()
✅
You can reference variable in another definition
:root {
--border-width: 10px;
--border: var(--border-width) solid #000;
}
div {
border: var(--border);
}
After some testing, I found the order doesn't matter. You can reference a latter variable in an earlier definition. But coming from JavaScript where you should always use the variable after it's been defined, this seems a bit off to me 😅
/* This also works */
:root {
--border: var(--border-width) solid #000;
--border-width: 10px;
}
Overriding CSS Variable Values
The great thing is you can override the global value, so can set something unique to a specific context.
:root {
--default-color: pink;
}
.content {
/* Override the global css variable */
--default-color: green;
}
p {
color: var(--default-color);
}
<p>Default "Pink" color</p>
<div class="content">
<p>Overridden "Green" color</p>
</div>
Setting Fallback Value
What happens when you use a variable that has never been assigned 🤔
p {
color: var(--color);
}
The answer is NOTHING. Your app doesn't break. I guess that's nice. But if that seems a bit risque, you can set a Fallback Value.
p {
color: var(--color, pink);
}
<p>Pink color</p>
And if you do define it, the defined color will just take over.
p {
--color: black;
color: var(--color, pink);
}
<p>Black color</p>
Using CSS Variable in JavaScript
The best thing about using CSS variable instead of Sass variable, is that you can access it in JavaScript! And you know when JS joins the party, it's going to get crazy 😆
Let's go over the basics usage and see how we can retrieve and set our CSS variables.
Retrieve from inline style
If you set your CSS variable via inline style.
<p style="--color: red"></p>
Then you retrieve your value with getPropertyValue()
:
// Get our <p> element
const element = document.querySelector('p');
// Retrieve our CSS variable "--color"
element.style.getPropertyValue('--color'); // 'red'
Retrieve from inline or css file
If you set your CSS variable in your style tag or an external CSS file.
<style>
p {
--color: red;
}
</style>
Then you need to use this first getComputedStyle()
:
// Get our <p> element
const element = document.querySelector('p');
// Retrieve our CSS variable "--color"
getComputedStyle(element).getPropertyValue('--color'); // 'red'
And yes, you can also use this way to retrieve your inline style as well:
<p style="--color: red"></p>
// Get our <p> element
const element = document.querySelector('p');
// Retrieve our CSS variable "--color"
getComputedStyle(element).getPropertyValue('--color'); // 'red'
Setting a CSS Variable with JS
And to adjust your CSS variable, you just use setProperty
.
// Get our <p> element
const element = document.querySelector('p');
// Set our "--color" variable to be "blue"
element.style.setProperty('--color', 'blue');
Simple Example
Let's put everything together and look at a simple example. Here we want to check our text color when the text is clicked.
<p style="--color:red; color: var(--color)"></p>
// Get our <p> element
const element = document.querySelector('p');
// On click, change text from "red" to "blue"
element.addEventListener('click', function() {
element.style.setProperty('--color', 'blue');
});
Retrieve Global CSS Variable from JavaScript
If you set your CSS variable in the global scope. To retrieve the value in JavaScript, you will have to go with the getComputedStyle
route, but instead of passing the element, you just pass in document.documentElement
. So something like this:
:root {
--color: red;
}
getComputedStyle(document.documentElement).getPropertyValue('--color'); // "red"
Browser Support
Beside party 💩 Internet Explorer, the rest of the browsers are all game!
Community Input
@lisovskyvlad: IE11 :( There's JS polyfill but on our experience, it makes ie11 so slow, it's hardly possible to use :(
@phillipkent: Still always wonder why can't we just assume IE11 users are clearly okay with a terrible experience? Lol
☝️This is my favorite response ever. I'm definitely going to use this whenever I get asked to fix something in IE. I'm a huge advocate of accoutability. But this is the only time I'll say, "It's you, not me" 😂
@lfdn: Some neat things you can do with css variables is easily control font sizes, spacings, colors on different viewports/pages. You could even do dark mode really easily by changing some css variables.
@jhildenbiddle: Those looking for IE/legacy support for CSS custom properties (i.e. "CSS variables") can check out css-vars-ponyfill. Forgive the self promotion (I am the author), but I thought it would be helpful for those still burdened--as I was not too long ago--with IE/legacy support.
Community Examples
@dillonheadley: css vars are awesome. Here are some cool things I've been using them for. Flexible container widths without having to overwrite the rule: CodePen
@azzcatdesign: I'm totally on board with CSS variables! I've got CodePens where I worked out responsive typography, spacers, and containers using global and scoped variables plu with calc(). Even took it further with HSL colors and abstracting the separate values to local variables for button colors. You can't do the same kind of color edits in CSS with variables as you can with SCSS ie: darken(\$color, 10%) but I've found I'm not missing SCSS variables for color, just organizing differently.
- CodePen: Layout Overlay with Container & Grid Modifiers
- CodePen: Type Variables: Responsive Scale Ratios
- CodePen: Spacing Variables (Fibonacci)
- CodePen: HSL Custom Properties for States
Resources
- MDN Web Docs: CSS Variables
- MDN Web Docs: Using CSS custom properties (variables)
- CSS Tricks: What is the difference between CSS variables and preprocessor variables?
- freeCodeCamp: Everything you need to know about CSS Variables
- flaviocopes: CSS Variables
- MDN Web Docs: getComputedStyle
Originally published at www.samanthaming.com
Thanks for reading ❤
Say Hello! Instagram | Twitter | Blog | SamanthaMing.com
Top comments (58)
Can I just add that if you use calc (or nested calc) and JavaScript update vars and CSS vars you can have it so one js update of a variable changes a lot of logic which can all be handled in the CSS. It's a very powerful workflow. In fact so much so I am writing a language like tailwind just for this workflow.
that's super cool! ...btw, do you mind explaining nested
calc
? 🙂Sure, it's not widely known or atleast it wasn't usefull to nest calc function given that before variables, values where essentially hard coded.
Okay this is a terrible example but it does illustrate how CSS can become config based and calc can do most of the work.
Oh cool!!! That’s super neat...I got to read this a few more time to understand it 😅...thanks so much for explaining it! Love learning new things ⭐️⭐️⭐️
Your not the only one, I found this out recently, didn't know calc was nestable, your most welcome.
Can you explain what the code snippet does, please. Or can you direct me to some articles in which it is elaborated your topic please.
I wasn't sure what specifically you wanted to know but, AFAIK, there are no specific posts on the topic, I may have one (I have hundreds of posts so it might take some time to find).
What does it do? its a simple implementation of a 12 column grid layout normally calculated via a pre-processor, what it does is not so important, how it does it is whats interesting here.
The short story is:
CSS is calculated by the browser, you might consider this "run-time" for css, at this point a few things are possible, bellow is a broken down list of the things I have use and what they do:
vw units:
100 vw
is the full viewport width as computed pixels, it is not 100% of the parent container.css variables:
--some-variable: red;
stores a value,var(--some-variable)
computes the valuecalc(): runtime maths such as
calc(100% + 20px)
which is cool, but you can also just add or subtract numbers and make calculations normally computed in css pre-processorsOh yes and lastly, I nested a calc() inside another calc to achieve complex maths
Thank you for the reply.
But I was implying explanation of your nested calc function. It would be great if you could elaborate on that one as well please, if you don't mind of course.
developer.mozilla.org/en-US/docs/W...
CSS calc 'calculate' is built into CSS and can be nested, the full documention can be found above.
However nesting refers to the fact that calc exaluates to a unit so then
calc(calc(2px + 4px) + 4px)
10 pixels
But this is particularly useful for complex math with variables because variables can change in media query and stateful circumstances (:hover, :focus etc)
thanx
Thank you so much! I've always been a CSS advocate but since I discovered Sass and its variables and functions, I tend to neglect CSS... So, I'm excited to get back in tiny projects without preprocessor and, as you said, with JS in the party, it's going to get crazy 💯
I was that way for a long time, Sass become a must have for all my projects and I just bared with the burden of installing it even on the small apps 😓. No more! Now i can go native all the way. Very nice for sure! thumbs up to the CSS folks 👍
That feeling when you are developer for many years, though mostly not front-end, but doing UI chores for work or in own side-projects... And then suddenly learns such great news by lazily reading topics on DEV.
Thank you, Samantha! God bless your efforts on sharing such things to us, lazy people! :)
lol, awesome! so glad you found it helpful! 😆
for an even lazier experience, feel free to check out my twitter account. and you can skip reading the code notes completely 😆
I'll even include the link to make things easier 😂 twitter.com/samantha_ming
As far as I remember syntax in the following example is invalid:
We can not build up values in CSS the way it depicted in the example above,
we should always combine it with the
calc()
, like this:Great catch!!!! Let me fix that, thank you!!!! 💪
Thanks, Samantha!
I'm totally on board with CSS variables! I've got CodePens where I worked out responsive typography, spacers, and containers using global and scoped variables plu with
calc()
. Even took it further with HSL colors and abstracting the separate values to local variables for button colors. You can't do the same kind of color edits in CSS with variables as you can with SCSS ie:darken($color, 10%)
but I've found I'm not missing SCSS variables for color, just organizing differently.OH that's super cool! If you don't mind, can you send me the link to it? Would love to see how you organize your code with css variables 😄
Sure! Layout Overlay with Container & Grid Modifiers codepen.io/azzcatdesign/pen/PoovWmp; Type Variables: Responsive Scale Ratios codepen.io/azzcatdesign/pen/yLLWgbq; Spacing Variables (Fibonacci) codepen.io/azzcatdesign/pen/YzzbNQ...; and HSL Custom Properties for States codepen.io/azzcatdesign/pen/WNNBRj...
This is fantastic! Thanks for sharing! Let me add this to my code notes 👏
Yess CSS variables ftw. It's time to slowly get rid of scss. Other then nesting and some mixins it doesn't add a bunch of value now since css gets more of these features out of the box.
Some neat things you can do with css variables is easily control font sizes, spacings, colors on different viewports/pages. You could even do dark mode really easily by changing some css variables.
Dark mode is a huge beneficiary of CSS variable! let me add your input to my code notes! thanks for sharing 👏
css vars are awesome. Here's some cool things i've been using them for.
Flexible container widths without having to overwrite the rule:
Font styles management:
and declarative simple animations:
codepen.io/dillonbheadley/pen/oNXNyPa
fun stuff!
Thanks for sharing this @dillonheadley . Awesome work! It's always so helpful to see how people implement the tech in their own project. Let me link this in the code notes 👏
For sure! 👍🏼 Love your posts btw!
Here's one more to manage buttons with vars: codepen.io/dillonbheadley/pen/PoqWqxq
Your way of explaining things are funny and awesome.
Hahaha thanks! Finally someone actually said it’s funny! I failed as a stand up comic, so I’m practicing my routine in programming articles lol 😂
Such an amazing well written article @Samantha Ming! I 💕 your images and use of emoji is 👌.
Sadly I am in a company with crazy high IE usage. I get reports on occasion that things are broken.... Looks fine to me. $H!1! I forgot to double check IE, then am amazed at what seemingly simple things IE is missing.
Thank you for the kind words, glad you it helpful 😊
IE support 😖
@jhildenbiddle shared a polyfill he wrote that might help > dev.to/jhildenbiddle/comment/lmi3
Super thanks for the polyfill!! I will consider that. I had no idea such a core css feature could be polyfilled.
For now I have mostly settled on using styled components
Those looking for IE/legacy support for CSS custom properties (i.e. "CSS variables") can check out css-vars-ponyfill. Forgive the self promotion (I am the author), but I thought it would be helpful for those still burdened--as I was not too long ago--with IE/legacy support.
This is great John! Also thank you for being so transparent. I'll add it to my code notes in the community section 😊