How to conditionally load CSS and extend it using SASS/SCSS - css

Question

tl:dr version: is there a way to #extend a css class and not have the original class appear in my compiled css without changing all my css classes to %placeholder classes?
Short answer based on the below answers: it appears there is no way to do this unless you go through and convert the css to silent/placeholder classes e.g. convert .one{} to %one{} and even then that will cause problems with media queries.
I have a css file (lets call it "style.css") which contains 200+ CSS classes to style various elements like forms and buttons etc. What I want is to include some of those classes in a project and other classes from that file in other random projects/websites. With each new project I also want to give the classes random semantic class names of my choosing.
My preprocessor of choice when working with CSS is SCSS and I really need an answer that uses the power of SCSS.
Here is a quick example of what I'm talking about - loading css into a SCSS file and then extending that css with my own class names:
//style.css
.one {
color: red;
padding-top: 1px;
}
//style2.scss
#import "style.css";
.two {
#extend .one;
}
The problem here is that my SCSS file will compile to CSS and look like this:
//style2.css
.one {
color: red;
padding-top: 1px;
}
.two {
color: red;
padding-top: 1px;
}
But what I want to do is only include the second class, which I gave a special name.
I've tried a few ways of doing this but here's one example that does not work but is along the lines of what I was thinking I should be able to do:
A.) First, I grab the style.css file and chuck copy/paste it into a style.scss file.
B.) Second I wrap all the whole thing in a placeholder/silent class, like so:
//style.scss
%placeholder {
.one {
color: red;
padding-top: 1px;
}
}
C.) Then I import that SCSS file and try and extend a class of my choosing that is within the placeholder, like this:
//style2.scss
#import "style";
.two {
#extend .one;
}
When I try and compile this I get a blank css file (and rightly so for trying to be too tricky). The other thing I know is that you can't extend nested selectors so "#extend %placeholder .one;" is also out of the question.
My question is this: does anyone know of a way to import and then extend a css class so that the compiled result does not include the imported css?
The only other solution I can think of is to just delete the imported css from the top of my file before I let it out into the wild. But this is honestly less than ideal solution.
Thank you in advance to any answers :)

Answer 1

You're using placeholders incorrectly, the placeholder should simply be one, no need to wrap it. Try this:
// style.scss
%one {
color: red;
padding-top: 1px;
}
// style2.scss
#import "style";
.two {
#extend %one;
}
Note that there is an issue with this approach. While the outputted CSS is leaner than using a mixin (#include), you will not be able to use %one inside of any #media queries. Ie. this will not work:
// style2.scss
#import "style";
#media screen and (max-width:1024px) {
.two {
// This won't produce CSS as it's inside the media query
#extend %one;
}
}
The only way I'm aware to get around this is to use a mixin instead of a placeholder which will result in more CSS (if you use one more than once).
// style.scss
#mixin one() {
color: red;
padding-top: 1px;
}
// style2.scss
#import "style";
#media screen and (max-width:1024px) {
.two {
#include one();
}
}
I've detailed the difference in output between mixins and placeholder selectors on my blog if you're not aware.