DO MORE.WRITE LESS.

Eugene Nor

SoftServe

What is LESS?

Less – preprocessor language that extends usual CSS to make it more readable and maintainable.

Outputs the code to pure CSS Adds semantic and structure to

stylesheets Makes coding slightly faster …and fun (most of the time)

Example

Less code:

@base: #f938ab;

@text: saturate(@base, 5%);

.shadow(@style, @c: #f5f5f5) {

-webkit-box-shadow: @style @c;

box-shadow: @style @c;

border: 1px solid @c;

}

.box {

color: @text;

div {

.shadow(0 0 5px, @base)

}

}

CSS output:

.box {

color: #fe33ac;

}

.box div {

-webkit-box-shadow: 0 0 5px #fdcdea;

box-shadow: 0 0 5px #fdcdea);

border: 1px solid #fdcdea);

}

Some history

Less was created in 2009 by Alexis Sellier, more commonly known as @cloudhead. Originally written in Ruby, it was then ported to JavaScript.

In May 2012 Alexis relinquished control and development over to a core team of contributors who now manage, fix and extend the language.

Less is maintained by a group of invaluable core contributors, with the massive support and involvement of our community. 

Installation & usage

Less can be used on command line as Node package (make sure you have NodeJS installed):

npm install less –g

After successful installation you can use it next ways:

$ lessc styles.less - this will output the compiled CSS to stdout

$ lessc styles.less > styles.css - will output CSS to file styles.css

$ lessc styles.less > styles.css –x - will output minified CSS

Installation & usage

Also it’s possible to use LESS as a Grunt task:

npm install grunt-contrib-less --save-dev

Gruntfile:

less: { development: { options: { paths: ["assets/css"] }, files: { "path/to/result.css": "path/to/source.less" } }

grunt.loadNpmTasks('grunt-contrib-less');

Installation & usage

Include it a script file for the browser (not recommended for production). Make sure you include your stylesheets before the script. You can add some options for convenient debugging.

<script>

less = {

env: "development",

async: false,

fileAsync: false,

poll: 1000,

functions: {},

relativeUrls: false,

rootpath: ":/a.com/“

};

</script>

<script src="less.js"></script>

<script>less.watch();</script> <!—This enables live browser reload-->

Nested rules

Less allows you to nest selectors one into another just the same as they are placed in HTML:

Less code:

#header { color: black;

.navigation { font-size: 12px; } .logo { width: 300px; } }

CSS output:

#header { color: black; }

#header .navigation { font-size: 12px; }

#header .logo { width: 300px; }

Variables

Define variables and refer to them in your rules. When defining a variable twice, the last definition of the

variable is used, searching from the current scope upwards (scopes work just like in JavaScript)

@var: 0; .class1 { @var: 1; .class { @var: 2; three: @var; @var: 3; } one: @var; }

@nice-blue: #5B83AD; @light-blue: @nice-blue + #111; #header { color: @light-blue; border-color: @nice-blue; }

Arithmetic

Any number, color or variable in Less can be operated:

@base: 5%; @filler: @base * 2; @other: @base + @filler; color: #888 / 4; background-color: @base-color + #111; height: 100% / 2 + @filler;

LESS understands units well:

@var: 1px + 5; //6px

Mixins

Mixins are a way of including ("mixing in") a bunch of properties from one rule-set into another rule-set

Definition:

.bordered { border-top: dotted 1px black; border-bottom: solid 2px black; }

.no-decoration { text-decoration: none; }

Usage:

#menu a { color: #111; .no-decoration; }

.post a { color: red; .bordered;}

Mixins without output

Mixin can be created without output to result style:

CSS output:

.my-mixin {

color: black;

}

.class {

color: black;

background-color: white;

}

Less code:

.my-mixin {

color: black;

}

.my-other-mixin() {

background-color: white;

}

.class {

.my-mixin;

.my-other-mixin;

}

This!

& symbol represents the current parent selector (such as this keyword in JavaScript)

CSS output:

button :hover { border: 1px solid red;}

Less code:

.my-hover-mixin() { &:hover { border: 1px solid red; }}

button { .my-hover-mixin();}

Parametric mixins

Pass parameters to mixins to make them more versatile. It’s possible to declare default values of parameters in

mixin definition.

Definition:

.border-radius(@radius: 10px) { -webkit-border-radius: @radius; -moz-border-radius: @radius; border-radius: @radius; }

Usage:

#header { .border-radius(4px); }

.button { .border-radius(6px); }

Mixin guards

Guards in Less are useful for conditional declaration of mixins Guards allows you to check value of a parameter as well as its

type

.mixin (@a) when (lightness(@a) >= 50%) { background-color: black; }

.mixin (@a) when (lightness(@a) < 50%) { background-color: white; }

.mixin (@a) { color: @a; }

.another-mixin (@a; @b: 0) when (isnumber(@b)) { ... }

.another-mixin (@a; @b: black) when (iscolor(@b)) { ... }

Return variables

All variables defined in a mixin are visible and can be used in caller's scope. This allows to create mixins that can be used almost like a functions

.average (@x, @y) { @average: ((@x + @y) / 2); }

div { .average (16px, 50px); //"call" the mixin padding: @average; //use its "return" value (33px)}

Merging rules

The merge feature allows for aggregating values from multiple properties

CSS output:

.myclass { box-shadow: inset 0 0 10px #555, 0 0 20px black; }

Less code:

.mixin() { box-shadow+: inset 0 0 10px #555; }

.myclass { .mixin(); box-shadow+: 0 0 20px black;}

Mixin libraries3L Mixins library

animate Library of CSS3 keyframe animations

Clearless Collection of mixins

CssEffects Collection of CSS style effects

Cssowl Mixin library

cube.less Animated 3D cube using only CSS

Hexagon Generate CSS hexagons with custom size and color

LESS Elements Set of mixins

LESS Hat Mixins library

LESS-bidi Set of mixins for creating bi-directional styling

media-query-to-type

Media Queries to Media Types with Less

More-Colors.lessVariables for easier color manipulation while you design in the browser

More.less Mixins, animations, shapes and more

Oban Collection of mixins

PrebootCollection of variables and mixins. The precursor to Bootstrap

Shape.LESS Collection of mixins for various shapes

tRRtoolbelt.less Mixins and functions for common actions

Bundles

Bundles are way to define a bunch of variables and mixins under one namespace

Usage:

#header a { color: orange; #bundle > .button; }

Definition:

#bundle { .button { display: block; border: 1px solid black; background-color: grey; &:hover { background-color: white; } } .tab { ... } .citation { ... } }

Functions

Less has a powerful set of a built-in functions and operations.

There are: Math functions: sqrt, pow, abs, sin, cos… String functions: escape, format, replace… List functions: length, extract... Color functions: mix, spin, lighten… And more…

Functions

Type checking operations are available:

isnumber isstring iscolor iskeyword isurl ispixel isem ispercentage isunit

For instance this is how isnumber works:

isnumber(#ff0); // false

isnumber(blue); // false

isnumber("string"); // false

isnumber(1234); // true

isnumber(56px); // true

isnumber(7.8%); // true

isnumber(keyword); // false

isnumber(url(...)); // false

Color operations

saturate(hsl(90%, 80%, 50%), 20%)

desaturate(hsl(90%, 80%, 50%), 20%)

lighten(hsl(90%, 80%, 50%), 20%)

darken(hsl(90%, 80%, 50%), 20%)

fade(hsl(90%, 80%, 50%), 10%)

spin(hsl(90%, 80%, 50%), 30)

greyscale(hsl(90%, 80%, 50%))

mix(#ff0000, #0000ff, 50%)

Less includes a lot of operations to make color operating quick and easy:

Color blending

multiply(#ff6600, #333333);

screen(#ff6600, #333333);

overlay(#ff6600, #333333);

softlight(#ff6600, #333333);

hardlight(#ff6600, #333333);

difference(#ff6600, #333333);

exclusion(#ff6600, #333333);

average(#ff6600, #333333);

negation(#ff6600, #333333);

You can easily blend colors in your rules with special functions:

@Import

@import keyword allows to Import styles from other style sheets. @import can be used in any line of file.

@import "foo"; // foo.less is imported @import "foo.less"; // foo.less is imported @import "foo.php"; // foo.php imported as a less file @import "foo.css"; // statement left in place, as-is

Less offers several extensions to the @import to provide more flexibility

Syntax: @import (option) "filename"; Options:

• reference: use a Less file but do not output it• inline: include the source file in the output but do not process it• less: treat the file as a Less file, no matter what the file extension• css: treat the file as a CSS file, no matter what the file extension• once: only include the file once (this is default behavior)• multiple: include the file multiple time

Tools & GUIs for LESS

Crunch! - Less editor for Windows and Mac.

Mixture - rapid prototyping and static site generation tool for designers and developers

SimpLESS - minimalistic Less compiler. Just drag, drop and compile.

Koala - cross-platform GUI application for compiling less, sass and coffeescript.

Prepros App -

free and open source app that can compile less, sass, stylus, jade, haml and much more.

WinLess - Less compiler with a set of options

LiveReload - live editor. CoffeeScript, SASS, Less and others just work.

Support in IDEs

LESS is supported by all popular editors and IDE’s (natively or with plugins help), including:

Visual Studio Eclipse Sublime Text 2 & 3 TextMate Vim NetBeans (built-in syntax highlighting) jetBrains WebStorm and PhpStorm (built-in support) CodeLobster (built-in syntax highlighting) Dreamweaver Notepad++ 6.x

LESS is used by:

Alternatives

Stylus - Expressive, dynamic, robust CSS

SASS - CSS with superpowers

Links

lesscss.org official LESS website

https://github.com/less/less.js GitHub repo

https://www.npmjs.org/package/grunt-contrib-less

Grunt plugin

http://winless.org/online-less-compiler

Online compiler

https://github.com/Asual/lesscss-engine

Java LESS port

http://www.dotlesscss.org .NET LESS port

http://crunchapp.net Crunch! editor website

http://learnboost.github.io/stylus/ Stylus website

http://sass-lang.com/ SASS website

Any questions?