Modify Alpha Opacity of Less Variable

Modify alpha opacity of LESS variable

The site documentation gives the answer:

background: fade(@blue, 20%);

The function name is fade not alpha according to that document.

How do I apply opacity to a CSS color variable?

You can't take an existing color value and apply an alpha channel to it. Namely, you can't take an existing hex value such as #f0f0f0, give it an alpha component and use the resulting value with another property.

However, custom properties allow you to convert your hex value into an RGB triplet for use with rgba(), store that value in the custom property (including the commas!), substitute that value using var() into an rgba() function with your desired alpha value, and it'll just work:

:root {
  /* #f0f0f0 in decimal RGB */
  --color: 240, 240, 240;
}

body {
  color: #000;
  background-color: #000;
}

#element {
  background-color: rgba(var(--color), 0.8);
}

<p id="element">If you can see this, your browser supports custom properties.</p>

Is it possible to change only the alpha of a rgba background colour on hover?

This is now possible with custom properties:

.brown { --rgb: 118, 76, 41; }
.green { --rgb: 51, 91, 11; }

a { display: block; position: relative; }
div { position: absolute; bottom: 0; background-color: rgba(var(--rgb), 0.8); }
a:hover div { background-color: rgba(var(--rgb), 1); }

To understand how this works, see How do I apply opacity to a CSS color variable?

If custom properties are not an option, see the original answer below.

---

Unfortunately, no, you'll have to specify the red, green and blue values again for each individual class:

a { display: block; position: relative; }

.brown { position: absolute; bottom: 0; background-color: rgba(118, 76, 41, 0.8); }
a:hover .brown { background-color: rgba(118, 76, 41, 1); }

.green { position: absolute; bottom: 0; background-color: rgba(51, 91, 11, 0.8); }
a:hover .green { background-color: rgba(51, 91, 11, 1); }

You can only use the inherit keyword alone as a value for the property, and even then the use of inherit isn't appropriate here.

Is it possible to assign opacity to a SCSS hex color variable, re using that variable?

Here you go...

WRONG:

$first-with-opacity: rgba($color: $first-color, alpha: 0.05);

CORRECT:

$first-with-opacity: rgba($first-color, 0.05);

LESSCSS method with IE FIlter Alpha Opacity CSS

In dotless, do this. (I would NOT recommend script tags - they are ugly, language specific and not supported by dotless).

.opacity (@opacity) {
    @opacityPercentage: @opacity * 100;
    opacity: @opacity;
    -ms-filter: ~"progid:DXImageTransform.Microsoft.Alpha(opacity=(@{opacityPercentage}))"; 
    filter: ~"alpha(opacity = (@{opacityPercentage}))";
}

in dotless 1.2.3 (when it is released in a couple of weeks, or github head, you should be able to do this...

.opacity (@opacity) {
    @opacityPercentage: @opacity * 100;
    opacity: @opacity;
    -ms-filter: progid:DXImageTransform.Microsoft.Alpha(opacity=(@opacityPercentage)); 
    filter: alpha(opacity = (@opacityPercentage));
}

and re: the comment from Mathletics, dotless is not "the worst compiler".. It matches less.js up to 1.1.5, soon to be 1.2.2 and many of the 600 bugs against less.js are fixed in dotless. You may have used dotless over 8 months ago, but things change and bugs are fixed... dotless also has better support for comments and variable scoping.

background opacity less mixin possible?

If I understand you correctly, then not in the sense that you are trying to do - @existing-bg would need to be able to assess the current BG colour at RUNTIME but essentially, we use LESS at compile time. The answer would be to put the colour (red) in a variable and supply the same variable in both places.

@existing: #ff0000;
div {
     background-colour: @existing;
}

.opacity {
     background-color: fade(@existing, 50%)
}

CSS opacity only to background color, not the text on it?

It sounds like you want to use a transparent background, in which case you could try using the rgba() function:

rgba(R, G, B, A)

R (red), G (green), and B (blue) can be either <integer>s or <percentage>s, where the number 255 corresponds to 100%. A (alpha) can be a <number> between 0 and 1, or a <percentage>, where the number 1 corresponds to 100% (full opacity).

RGBa example

background: rgba(51, 170, 51, .1)    /*  10% opaque green */ 
background: rgba(51, 170, 51, .4)    /*  40% opaque green */ 
background: rgba(51, 170, 51, .7)    /*  70% opaque green */ 
background: rgba(51, 170, 51,  1)    /* full opaque green */ 

A small example showing how rgba can be used.

As of 2018, practically every browser supports the rgba syntax.

Programmatically add opacity to a color in Typescript

Well, if you program it, it is ...

function addAlpha(color: string, opacity: number): string {
    // coerce values so ti is between 0 and 1.
    const _opacity = Math.round(Math.min(Math.max(opacity || 1, 0), 1) * 255);
    return color + _opacity.toString(16).toUpperCase();
}
addAlpha('FF0000', 1); // returns 'FF0000FF'
addAlpha('FF0000', 0.5); // returns 'FF000080'

Of course, you can improve this function by checking that color has the proper format, by using regular expressions.

---

Related Topics