The browser DOES NOT convert pre-processed
(LESS, SCSS, Compass) CSS rules.
You need to use a build script/compiler BEFORE linking a normal CSS file to your HTML. This process converts SCSS/LESS -> CSS for your browser to render.
You can use Webpack, Grunt, Gulp, or even desktop/GUI tools to do this.
You can also use a javascript parser to inject the final CSS into the page onLoad
but this has performance implications and IS NOT recommended.
solved How browsers will convert mixins to regular css [closed]