§Using LESS CSS

LESS CSS is a dynamic stylesheet language. It allows greater flexibility in the way you write CSS files: including support for variables, mixins and more.

Compilable assets in Play must be defined in the app/assets directory. They are handled by the build process, and LESS sources are compiled into standard CSS files. The generated CSS files are distributed as standard resources into the same public/ folder as the unmanaged assets, meaning that there is no difference in the way you use them once compiled.

Note that managed resources are not copied directly into your application public folder, but maintained in a separate folder in target/scala-2.x.x/resources_managed.

For example a LESS source file at app/assets/stylesheets/main.less will be available as a standard resource at public/stylesheets/main.css.

LESS sources are compiled automatically during a compile command, or when you refresh any page in your browser while you are running in development mode. Any compilation errors will be displayed in your browser:

§Working with partial LESS source files

You can split your LESS source into several libraries, and use the LESS import feature.

To prevent library files from being compiled individually (or imported) we need them to be skipped by the compiler. To do this, partial source files must be prefixed with the underscore (_) character, for example: _myLibrary.less. To configure this behavior, see the Configuration section at the end of this page.

§Layout

Here is an example layout for using LESS in your project:

app
 └ assets
    └ stylesheets
       └ main.less
       └ utils
          └ _reset.less
          └ _layout.less    

With the following main.less source:

@import "utils/_reset.less";
@import "utils/_layout.less";

h1 {
    color: red;
}

The resulting CSS file will be compiled as public/stylesheets/main.css, and you can use this in your template as any regular public asset. A minified version will also be generated.

<link rel="stylesheet" href="@routes.Assets.at("stylesheets/main.css")">

<link rel="stylesheet" href="@routes.Assets.at("stylesheets/main.min.css")">

§Configuration

The default behavior of compiling every file that is not prepended by an underscore may not fit every project; for example if you include a library that has not been designed that way.

This can be configured in project/Build.scala by overriding the lessEntryPoints key. This key holds a PathFinder.

For example, to compile app/assets/stylesheets/main.less and nothing else:

 import play.Keys._
 
...

 val main = play.Project(appName, appVersion, appDependencies).settings(
   lessEntryPoints <<= baseDirectory(_ / "app" / "assets" / "stylesheets" ** "main.less")
 )

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