Change opacity depending on viewport size

417 Views Asked by Jakub Janowski At 09 November 2022 at 21:14

I'm trying to change element's opacity based on how wide the browser's window is in a continuous manner. Ideally, I would like to get a unit-less value from calc by dividing current viewport's width by some constant, like this:

opacity: clamp(0.5, calc(100vw / 1000px), 1);

but calc doesn't allow dividing by a unit. Is there any other way to achieve this in CSS?

Original Q&A

There are 1 best solutions below

Mauro Aguilar On 09 November 2022 at 22:26

Unless you define some default opacities for different breakpoints using media queries I think you'd have to rely on js to achieve this. Seems like it is not possible to strip units in CSS unfortunately.

I was playing around with this in different ways and this was the closest behavior I could get:

btw you can do basic math expressions without calc function as per docs: https://developer.mozilla.org/en-US/docs/Web/CSS/clamp#parameters

var r = document.querySelector(':root');

function log() {
  var width = window.innerWidth;
  var opacity = getComputedStyle(document.body).opacity;
  r.style.setProperty('--vp-width', width);
  console.log(width, opacity);
}

window.addEventListener('resize', log);
log();

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html, body  {
  width: 100%;
  height: 100%;
}

body {
  opacity: clamp(0.5, var(--vp-width) / 1000, 1);
}

.content {
  background: black;
  height: 100%;
}

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div class="content"></div>
</body>
</html>

Note: This is definitely not the best way to change opacity dynamically using js!

Change opacity depending on viewport size

There are 1 best solutions below

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