#LESS is more

1. Nested Selectors
2. Mixins
3. Functions
4. Colours

##LESS nests selectors

nav {
    width: 100%;
    height: 50px;
    float: left;
    ul {
        width: 100%;
        height: 100%;
        li {
            float: left
            width: 20%;
            margin: 10px 30px;
            &:first-child {
                margin: 0;
            }
            > a {
                width: auto;
                text-align: center;
            }
        }
    }
}

Becomes:

nav {
    width: 100%;
    height: 50px;
    float: left;
}
nav ul {
    width: 100%;
    height: 100%;
}
nav ul li {
    float: left
    width: 20%;
    margin: 10px 30px;
}
nav ul li:first-child {
    margin: 0;
}
nav ul li > a {
    width: auto;
    text-align: center;
}

##Mixins

.box-sizing () {
    -webkit-box-sizing: border-box;
    -moz-box-sizing:    border-box;
    box-sizing:         border-box;
}

.box {
    width: 20%;
    padding: 5px;
    .box-sizing.
}

Outputs:

.box {
    width: 20%;
    padding: 5px;
    -webkit-box-sizing: border-box;
    -moz-box-sizing:    border-box;
    box-sizing:         border-box;
}

---

They can also take in variables

.gradient(@start, @finish) {
    background-color: @start;
    background-image: -webkit-linear-gradient(top, @start, @finish);
    background-image:    -moz-linear-gradient(top, @start, @finish);
    background-image:     -ms-linear-gradient(top, @start, @finish);
    background-image:      -o-linear-gradient(top, @start, @finish);
    background-image:         linear-gradient(to bottom, @start, @finish);
}

header {
    .gradient(#333,#000);
}
body {
    .gradient(#000,#333);
}

Outputs:

header {
    background-color: #333333;
    background-image: -webkit-linear-gradient(top, #333333, #000000);
    background-image:    -moz-linear-gradient(top, #333333, #000000);
    background-image:     -ms-linear-gradient(top, #333333, #000000);
    background-image:      -o-linear-gradient(top, #333333, #000000);
    background-image:         linear-gradient(to bottom, #333333, #000000);
}
body {
    background-color: #000000;
    background-image: -webkit-linear-gradient(top, #000000, #333333);
    background-image:    -moz-linear-gradient(top, #000000, #333333);
    background-image:     -ms-linear-gradient(top, #000000, #333333);
    background-image:      -o-linear-gradient(top, #000000, #333333);
    background-image:         linear-gradient(to bottom, #000000, #333333);
}

---

Can have defaults:

.box-sizing (@type: border-box) {
    -webkit-box-sizing: @type;
    -moz-box-sizing:    @type;
    box-sizing:         @type;
}

.box {
    width: 20%;
    padding: 5px;
    .box-sizing.
}

Outputs:

.box {
    width: 20%;
    padding: 5px;
    -webkit-box-sizing: border-box;
    -moz-box-sizing:    border-box;
    box-sizing:         border-box;
}

##Functions

Can have mixins based on criteria:

.set-bg-color (@text-color) when (lightness(@text-color) >= 50%) { 
  background: black;
}
.set-bg-color (@text-color) when (lightness(@text-color) < 50%) { 
  background: #ccc;
}

body {
    color: #333;
    .set-bg-color(#333);
}

##Colours

LESS also has functions that work specifically with numbers.

###darken()

@color: #FFF;
body {
    background-color: darken(@color, 20%);
}

###lighten()

@color: #3F3F3F;
body {
    background-color: lighten(@color, 20%);
    color: darken(@color, 20%);
}