Analysis of CSS variables variable
This article mainly introduces the analysis of CSS variables, which has certain reference value. Now I share it with everyone. Friends in need can refer to the previous words
Since then, there are no variables in CSS. To use CSS variables, you can only use precompilers such as SASS or LESS. With the release of the new draft, defining and using variables directly in CSS is no longer a fantasy. This article will introduce CSS variables in detail
Basic usage
CSS variables are entities defined by CSS authors that contain specific values to be reused throughout the document. Use custom attributes to set variable names, and use specific var() to access
Compatibility: Mobile and IE browsers are not compatible
[Declaration of variables]
Variables must start with
--. For example, --example-variable: 20px means assigning 20px to the --example-varibale variable. You can place the statement declaring the variable within any element. If you want to set a global variable, you can set it to: root, body or html
:root{
--bgColor:#000;
}The variable declaration is just like the ordinary style declaration statement. You can also use the inline style
<body style="--bgColor:#000">
The variable declaration statement must be included in an element and cannot be placed randomly.
//错误 <style> --bgColor:#000; </style>
【Use variables】
Use the var() function to use variables, and can be used anywhere. For example: var(--example-variable) will return the value corresponding to --example-variable
<body style="--bgColor:#000;">
<p style="width: 100px;height: 100px;background-color: var(--bgColor)"></p> </body>The var() function also has an optional parameter, which is used to set the default value when the variable cannot obtain the value. When, the default value is used
<body>
<p style="width: 100px;height: 100px;background-color: var(--bgColor,pink)"></p> </body>Inheritance and cascading
Like ordinary style attributes, variable attributes also support inheritance and cascading. In the following example, the variable value of the body element is green, and the variable value of the p element is red; based on the principle of cascading, the final background color of the p element is red
<body style="--bgColor:green;">
<p style="width: 100px;height: 100px;--bgColor: red;background-color: var(--bgColor,pink)"></p> </body>Composition and calculation
【 Combination】
CSS variables can be used in combination
<style>.box{
--top:20%;
--left:30%;
width: 100px;
height: 100px;
background-image: url(img/24/xiaoshu.jpg);
background-position: var(--left) var(--top);}</style><p class="box"></p>However, CSS variables cannot be combined in the following forms. var(--color1)var(--color2) is not recognized by the browser. If separated, such as var(--color1) var(--color2), it will be parsed as #333 and cannot be recognized by the browser
<style>.box{
--color1:#;
--color2:333;
width: 100px;
height: 100px;
background-color: var(--color1)var(--color2);}</style><p class="box"></p>【Calculation】
Variables and ordinary styles The values are the same. In addition to combination, you can also use calc for calculation
<style>.box{
--borderWidth:2px;
width: 100px;
height: 100px;
background-color:lightblue;
border-left: calc(var(--borderWidth) * 2) solid black;}</style><p class="box"></p>JS
CSS variables can interact with JS. It should be noted that you can only use the getPropertyValue() and setProperty() methods, but not the style attribute
[style attribute]
<p id="box" style="--color:lightgreen;background-color: var(--color)"></p> <script> var oBox = document.getElementById('box'); console.log(oBox.style['--color']); //undefined</script>
[getPropertyValue()]
<p id="box" style="--color:lightgreen;background-color: var(--color)"></p> <script> var oBox = document.getElementById('box'); console.log(oBox.style.getPropertyValue('--color'));//'lightgreen'</script>
【setProperty()】
<style>#box{
--color:lightgreen;
background-color: var(--color);
width: 100px;
height: 100px;
display:inline-block;}</style><button id="btn" type="button">变浅蓝</button><p id="box"></p> <script>var oBox = document.getElementById('box');var oBtn = document.getElementById('btn');
oBtn.onclick = function(){
oBox.style.setProperty('--color','lightblue');
}</script>Not supported
One thing to note is that the variable is not supported!important
.box{
--color:red;
width: 100px;
height: 100px;
background-color:--color !important;
}</style><p class="box"></p>The chrome browser screenshot is as follows
Purpose
1. Maintainability
Maintaining a color scheme or size scheme in a web page means that some styles are used multiple times in the CSS file appear and are reused. When modifying a plan, whether it is adjusting a certain style or completely modifying the entire plan, it will become a complex problem, and simple search and replacement is not enough. At this time, CSS variables come in handy
:root{
--mainColor:#fc0;
}
.p1{
color:var(--mainColor);
}
.p2{
color:var(--mainColor);
}2. Semantic
The second advantage of variables is that the name itself contains semantic information. CSS files become readable and understandable. main-text-color is easier to understand than #fc0 in the document, especially when the same color appears in different files
3. More convenient implementation of @media media query
Generally, media queries are as follows
<style>.box{
width: 100px;
height: 100px;
padding: 20px;
margin: 10px;
background-color: red}@media screen and (max-width:600px) {
.box{
width: 50px;
height: 50px;
padding: 10px;
margin: 5px;
}}</style><p class="box"></p>However, if you use variables, you can streamline the code
<style>.box{
--base-size:10px;
width: calc(var(--base-size) * 10);
height: calc(var(--base-size) * 10);
padding: calc(var(--base-size) * 2);
margin: calc(var(--base-size) * 1);
background-color: red;}@media screen and (max-width:600px) {
.box{
--base-size:5px;
}}</style><p class="box"></p>The above is the entire content of this article, I hope it will be helpful to everyone's learning, more Please pay attention to the PHP Chinese website for related content!
Related recommendations:
Analysis of the positon attribute of CSSHow to set placeholder through css
The above is the detailed content of Analysis of CSS variables variable. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
Vue 3
Apr 02, 2025 pm 06:32 PM
It's out! Congrats to the Vue team for getting it done, I know it was a massive effort and a long time coming. All new docs, as well.
Building an Ethereum app using Redwood.js and Fauna
Mar 28, 2025 am 09:18 AM
With the recent climb of Bitcoin’s price over 20k $USD, and to it recently breaking 30k, I thought it’s worth taking a deep dive back into creating Ethereum
Can you get valid CSS property values from the browser?
Apr 02, 2025 pm 06:17 PM
I had someone write in with this very legit question. Lea just blogged about how you can get valid CSS properties themselves from the browser. That's like this.
Stacked Cards with Sticky Positioning and a Dash of Sass
Apr 03, 2025 am 10:30 AM
The other day, I spotted this particularly lovely bit from Corey Ginnivan’s website where a collection of cards stack on top of one another as you scroll.
A bit on ci/cd
Apr 02, 2025 pm 06:21 PM
I'd say "website" fits better than "mobile app" but I like this framing from Max Lynch:
Comparing Browsers for Responsive Design
Apr 02, 2025 pm 06:25 PM
There are a number of these desktop apps where the goal is showing your site at different dimensions all at the same time. So you can, for example, be writing
Using Markdown and Localization in the WordPress Block Editor
Apr 02, 2025 am 04:27 AM
If we need to show documentation to the user directly in the WordPress editor, what is the best way to do it?
Why are the purple slashed areas in the Flex layout mistakenly considered 'overflow space'?
Apr 05, 2025 pm 05:51 PM
Questions about purple slash areas in Flex layouts When using Flex layouts, you may encounter some confusing phenomena, such as in the developer tools (d...
