CSS Equivalent of the "if" statement

Question

Is there any way to use conditional statements in CSS?

Answer 1

This has been implemented in modern browsers as of 2023. The :has feature lets you implement an if [query matches an element] then [select some other element to apply CSS to].

Here is an example:

/*main.css*/
#contactForm {
  display: none;
}

/* if #showForm input is checked then make #contactForm visible */
:has(input#showForm:checked) #contactForm {
  display: block;
}

<!--index.html-->

<input id='showForm' type="checkbox">
<br>
<div id='contactForm'>
  <textarea name="" id="" cols="30" rows="10"></textarea>
</div>

Answer 2

To select between two values in pure CSS you can use folowing math trick

Pseudocod:

if( valueSel < th) 
   return valueA
else
   return valueB

Pseudocod:

selector = (sign(valueSel-th)+1)/2
return valueA * (1-selector) + valueB * selector

CSS:

.some-class {
    --valueSel: /* Some Value - predicate */;
    --th: /* Some Treshold */;
    --valueA: /* Result A */;
    --valueB: /* Result B */;
    --selector: calc(clamp(0,tan( clamp(-1,var(--valueSel) - th, 1) ),1));
    --result: calc( var(--valueA) * (1 - var(--selector) ) + var(--valueB) * var(--selector) );    
}

It can be extended to selecting colors via mix-color

Answer 3

You can use combination of jquery and css classes i.e. I want to change a font color of certain element depending on the color of the background:

CSS:

.h3DarkMode{
    color: lightgray;
}
.h3LightMode{
    color: gray;
}

HTML:

<h3 class="myText">My Text Here...</h3>

JQuery:

var toggleMode = localStorage.getItem("toggleMode");
if (toggleMode == "dark"){
$(".myText").removeClass("h3LightMode").addClass("h3DarkMode");
}else{
$(".myText").removeClass("h3DarkMode").addClass("h3LightMode");
}

Answer 4

While this feels like a bit of a hack, and may not work perfectly in all browsers, a method I have used recently combines the fact that CSS (at least in Chrome) seems to ignore invalid values set on properties, and we can set custom properties that fall back to their default value when invalid.

(Note: I haven't deeply tested this, so treat it as a hacky proof of concept/possible idea)

The following is written in SCSS, but it should work just as well in standard CSS:

.hero-image {
    // CSS ignores invalid property values
    //   When this var is set to an image URL, the browser will ignore it
    //   When this var isn't set, then we will use the default fallback for the var, which is 'none'
    display: var(--loading-page-background-image, none);

    // This part isn't directly relevant to my 'if' example, but shows how I was actually using this custom property normally
    background-image: var(--loading-page-background-image, none);
}

I'm setting the custom property from JavaScript / React, but it would likely work regardless of how you set it:

// 'true' case
const chosenLoaderUrl = "https://www.example.com/loader.png";

// 'false' case
//const chosenLoaderUrl = "";

// containerRef is just a reference to the div object, you could get this with
//   jquery or however you need. Since I'm in React, I used useRef() and attached 
//   that to my div
containerRef.current.style.setProperty(
  "--loading-page-background-image",
  `url(${chosenLoaderUrl})`
);

When chosenLoaderUrl is set to my url, that url is an invalid value for the display property, so it seems to get ignored.

When chosenLoaderUrl is set to an empty value, it falls back to the default value in my var() statement, so sets display to none

I'm not sure how 'generalisable' this concept it, but figured I would add it to the other suggestions here in case it is useful to anyone.

Answer 5

CSS has become a very powerful tool over the years and it has hacks for a lot of things javaScript can do

There is a hack in CSS for using conditional statements/logic.

It involves using the symbol '~'

Let me further illustrate with an example.

Let's say you want a background to slide into the page when a button is clicked. All you need to do is use a radio checkbox. Style the label for the radio underneath the button so that when the button is pressed the checkbox is also pressed.

Then you use the code below

.checkbox:checked ~ .background{
opacity:1
width: 100%
}

This code simply states IF the checkbox is CHECKED then open up the background ELSE leave it as it is.

Answer 6

Changing your css file to a scss file would allow you to do the trick. An example in Angular would be to use an ngClass and your scss would look like:

 .sidebar {
    height: 100%;
    width: 60px;

    &.is-open {
        width: 150px
    }
} 

Answer 7

I'd say the closest thing to "IF" in CSS are media queries, such as those you can use for responsive design. With media queries, you're saying things like, "If the screen is between 440px and 660px wide, do this". Read more about media queries here: http://www.w3schools.com/cssref/css3_pr_mediaquery.asp, and here's an example of how they look:

@media screen and (max-width: 300px) {
  body {
     background-color: lightblue;
  }
}

That's pretty much the extent of "IF" within CSS, except to move over to SASS/SCSS (as mentioned above).

I think your best bet is to change your classes / IDs within the scripting language, and then treat each of the class/ID options in your CSS. For instance, in PHP, it might be something like:

<?php
  if( A > B ){
echo '<div class="option-a">';
} 
    else{
echo '<div class="option-b">';
}
?>

Then your CSS can be like

.option-a {
background-color:red;
}
.option-b {
background-color:blue;
}

Answer 8

CSS itself doesn't have conditional statements, but here's a hack involving custom properties (a.k.a. "css variables").

In this trivial example, you want to apply a padding based on a certain condition—like an "if" statement.

:root   { --is-big: 0; }

.is-big { --is-big: 1; }

.block {
  padding: calc(
    4rem * var(--is-big) +
    1rem * (1 - var(--is-big))
  );
}

So any .block that's an .is-big or that's a descendant of one will have a padding of 4rem, while all other blocks will only have 1rem. Now I call this a "trivial" example because it can be done without the hack.

.block {
  padding: 1rem;
}

.is-big .block,
.block.is-big {
  padding: 4rem;
}

But I will leave its applications to your imagination.

Answer 9

The @supports rule (92% browser support July 2017) rule can be used for conditional logic on css properties:

@supports (display: -webkit-box) {
    .for_older_webkit_browser { display: -webkit-box }
}

@supports not (display: -webkit-box) {
    .newer_browsers { display: flex } 
}

Answer 10

I would argue that you can use if statements in CSS. Although they aren't worded as such. In the example below, I've said that if the check-box is checked I want the background changed to white. If you want to see a working example check out www.armstrongdes.com. I built this for a client. Re size your window so that the mobile navigation takes over and click the nav button. All CSS. I think it's safe to say this concept could be used for many things.

     #sidebartoggler:checked + .page-wrap .hamb {
        background: #fff;
      }

// example set as if statement sudo code.

if (sidebaretoggler is checked == true) {
set the background color of .hamb to white;
}

Answer 11

There is no native IF/ELSE for CSS available. CSS preprocessors like SASS (and Compass) can help, but if you’re looking for more feature-specific if/else conditions you should give Modernizr a try. It does feature-detection and then adds classes to the HTML element to indicate which CSS3 & HTML5 features the browser supports and doesn’t support. You can then write very if/else-like CSS right in your CSS without any preprocessing, like this:

.geolocation #someElem {
   /* only apply this if the browser supports Geolocation */
}
.no-geolocation #someElem {
   /* only apply this if the browser DOES NOT support Geolocation */
}

Keep in mind that you should always progressively enhance, so rather than the above example (which illustrates the point better), you should write something more like this:

#someElem {
   /* default styles, suitable for both Geolocation support and lack thereof */
}
.geolocation #someElem {
   /* only properties as needed to overwrite the default styling  */
}

Note that Modernizr does rely on JavaScript, so if JS is disabled you wouldn’t get anything. Hence the progressive enhancement approach of #someElem first, as a no-js foundation.

Answer 12

No you can't do if in CSS, but you can choose which style sheet you will use

Here is an example :

<!--[if IE 6]>
Special instructions for IE 6 here
<![endif]-->

will use only for IE 6 here is the website where it is from http://www.quirksmode.org/css/condcom.html , only IE has conditional comments. Other browser do not, although there are some properties you can use for Firefox starting with -moz or for safari starting with -webkit. You can use javascript to detect which browser you're using and use javascript if for whatever actions you want to perform but that is a bad idea, since it can be disabled.

Answer 13

Your stylesheet should be thought of as a static table of available variables that your html document can call on based on what you need to display. The logic should be in your javascript and html, use javascript to dynamically apply attributes based on conditions if you really need to. Stylesheets are not the place for logic.

Answer 14

css files do not support conditional statements.

If you want something to look one of two ways, depending on some condition, give it a suitable class using your server side scripting language or javascript. eg

<div class="oh-yes"></div>
<div class="hell-no"></div>

Answer 15

No. But can you give an example what you have in mind? What condition do you want to check?

Maybe Sass or Compass are interesting for you.

Quote from Sass:

Sass makes CSS fun again. Sass is CSS, plus nested rules, variables, mixins, and more, all in a concise, readable syntax.

Answer 16

The only conditions available in CSS are selectors and @media. Some browsers support some of the CSS 3 selectors and media queries.

You can modify an element with JavaScript to change if it matches a selector or not (e.g. by adding a new class).