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Introduction to Less

This document describes the behavior of CSS pre-processor LESS.

Files import

In Shopsys Framework we implement Less by dividing styles into many Less components. Each component has its own file. Filename and component name are the same. We use @import command for joining all components contents into one compiled CSS file.

Here we can see syntax of @import command.

@import 'path/to/directory/component-filename.less';

Usage of @import command

The best way how to import all related files is to create one file, for example, named main.less. This file will contain only @import commands. Keep in mind where you place this file. Imported path depends on where this file is placed.

Unexpected behavior

There is one thing which you should keep in mind. When you try to import a file which does not exist in the given filepath, the compiler will try to find missing file in root directories of files, where is used @import.

Let us show this at the example. Assuming you have folder structure and files as it is shown below.

│── root-main.less
│── some-component.less
└─── B
    └── b-main.less
/** B/b-main.less */

@import "some-component.less";
/* some-component.less */

.some-component {
    color: red;
}
/* root-main.less */

@import "B/b-main.less";

Result CSS of this example will be.

.some-component {
    color: red;
}

As an explanation of this behavior, given in the example above, is that compiler is trying to find a file some-component.less firstly in the folder where is placed b-main.less, then in the directory of root-main.less. When it could not find required file in any directory, then it will throw an error during compiling.

Example 1 - Importing files from a current folder and its sub-folders

Let us have for this example following folder structure.

└── common
   └─── core
   |   └── variables.less
   └─── layout
   |   └── header.less
   │── helpers.less
   └── main.less

For importing of all files in folder common there will exist file main.less with the following code.

/* Import helper classes from current directory */
@import 'helpers.less';

/* Import all global variables from subdirectory core */
@import 'core/variables.less';

/* Import styles defined for header */
@import 'layout/header.less';

Example 2 - Importing files from another directory

Let us have for this example following folder structure.

└─── common
|   └─── core
|   |   └── variables.less
|   └─── layout
|   |   └── header.less
|   │── helpers.less
|   └── main.less
└─── domain2
    └─── core
    |   └── variables.less
    └─── layout
    |   └── footer.less
    └── main.less

We can see two files named main.less located in two different folders.

  • common/main.less will import only that type of files which defines common styles for all domains
  • domain2/main.less will import files which extend, add or modify styles for domain2

Now we want to extend styles for domain2 by changing default colors defined in core/variables.less and add styles for a footer. Code below shows up how would domain2/main.less look like.

@import '../common/main.less';

/* In order to extend, create or modify behavior of CSS
 * styles defined in directory common we have to import
 * styles related to domain2 after importing main.less
 * from directory common.
 */
@import 'core/variable.less';

@import 'layout/footer.less';