LESS CSS set variables in media query?

I'm working on a iPad-specific website. To make my website work on both the retina display iPad and older versions of iPads, I want to set a variable in LESS CSS in media query like:

@media all and (max-width: 768px) {
    @ratio: 1;
}

@media all and (min-width: 769px) {
    @ratio: 2;  
}

So when you are setting anything in pixels, you can do

width: 100px * @ratio;

But I got a compile error saying @ratio is not defined. Is it possible to have a workaround to make it work? Thanks.

Solution 1:

It would be nice, but this is impossible to do like this.

LESS compiles your media queries to actual media queries, so at compile time there is no indication of which media query will be relevant to the browser.

After compile time you just have CSS not less so you can't have variables anymore.

You can do this instead but it isn't as elegant:

@base_width: 100px;

@media all and (max-width: 768px) {
    .something {
        width: @base_width;
    }
}

@media all and (min-width: 769px) {
    .something {
        width: @base_width * 2;
    }
}

Solution 2:

I know I'm late with my answer but someone may find this useful.

You can move your styles to a separate file

// styles.less
.foo {
  width: 100px * @ratio;
}

And then import the file multiple times after changing variables' values

// main.less
@ratio: 1; // initial value

@media all and (max-width: 768px) {
  @ratio: 1;
  @import (multiple) "styles";
}

@media all and (min-width: 769px) {
  @ratio: 2;
  @import (multiple) "styles";
}

Note that (multiple) is important here

Compiled code will look like this

// main.css
@media all and (max-width: 768px) {
  .foo {
    width: 100px;
  }
}
@media all and (min-width: 769px) {
  .foo {
    width: 200px;
  }
}