LESS CSS is a dynamic stylesheet language that extends CSS by adding features like variables, mixins, operations, and functions. It allows CSS stylesheets to be more modular and reusable by adding parametric mixins, nesting rules, and importing files. Key features include using variables to store colors and values, defining mixins to group repeated CSS declarations, performing mathematical operations on values, and modifying colors with functions. LESS files are compiled into regular CSS files for browsers to use.

1. START USING LESS CSS
By: Ali MasudianPour <masud.amp@gmail.com>
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2. WHAT IS LESS CSS
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Dynamic CSS
• Less is a “dynamic stylesheet language”
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LESS extends CSS with dynamic behavior such as variables, mixins, operations and
functions.
•
LESS runs on both the server-side (with Node.js and Rhino) or client-side (modern
browsers only)
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3. COMPILING IN BROWSER
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Less.js will perform AJAX requests to grab your Less files, will then process those files to
convert them into CSS, and finally inject the resulting CSS in the head of your document.
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There is a bad thing about it
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if the user‟s JavaScript is deactivated, it will not work!
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4. LET‟S START
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LESS codes are written into a file with .less extension
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Variables
• Less variables can be declared and used with the @ symbol.
• Example:
@white: #fff;
.class{
background-color:@white;
}
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5. LET‟S START
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In addition, we can assign a variable to another
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For instance:
•
•
@myDefaultColor:@white;
MIXINS
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With Less we can define “mixins”, which are something comparable to functions in other programming languages. In Less they‟re used
to group CSS instructions.
.Round{
-webkit-border-radius:9999px;
-moz-border-radius:9999px;
border-radius:9999px;
}
#shape1{
.Round;
}
That‟s really simple!
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6. PARAMETRIC MIXINS
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In LESS we can define parametric mixins. So we can send parameters through mixins
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Example:
@defaultRadius:30px;
.RoundedShape(@radius:@defaultRadius){
-webkit-border-radius:@radius;
-moz-border-radius:@radius;
border-radius:@radius;
}
•
What an incredible feature!
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7. PARAMETRIC MIXINS
.Round{
.RoundedShape(9999px);
}
.RoundedSquare(@radius:@defaultRadius){
.RoundedShape(@radius);
}
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8. OPERATIONS
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One other powerful feature of Less is the ability to use mathematical operations in your
stylesheets.
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You can add, subtract, multiply and divide values
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Example
@defaultShapesWidth:200px;
@borderSize:@defaultShapesWidth * 0.1;
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it also works for colors
@defaultThemeColor:@lightBlue;
@borderColor:@defaultThemeColor - #222;
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9. COLOR FUNCTIONS
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Less provides the following color functions:
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darken() and lighten(), which add some black or white
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saturate() and desaturate(), to make a color more colorful or more grayscale
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Fadein() and fadeout, to increase or reduce transparency
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Spin(), which modifies the hue of the color
• Examples:
@borderColor: desaturate(@defaultColor,100%)
@borderColor: darken(desaturate($defaultColort,100%),20%)
@defaultColor:spin(@mycolor1,100)
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10. NESTED RULES
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When designing a complex page using css, you often have to chain selectors to aim a particular element in the DOM, like
this:
#header h1{}
#main h1{}
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With LESS you can nest rules inside parent rules to mimic the DOM structure:
#header {
h1{}
}
.shape{
}
•
&:hover{background-color:@myColor;}
This & symbol represents the current selected elements. It is the equivalent of “THIS” in most programming language
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11. IMPORTING
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It is a very good practice to separate your rules into different files instead of having a
1000 lines file.
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Importing a file into another LESS is as simple as that:
• @import “file2.less”;
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You can even omit the .less extension and just declare:
• @import “file2”;
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12. MODIFY VARIABLES
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modifyVars enables modification of LESS variables in run-time.
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When called with new value, the LESS file is recompiled without reloading.
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Usage:
Less.modifyVars({
„@color1‟:‟red‟,
„@color2‟: „blue‟
});
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13. THANK YOU
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References:
• Lesscss.org
• Verekia.com
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