Useful Mixins used in CSS

These are the mixins that come with the Static Website Boilerplate found here, they are a work in progress as I add to them when necessary.

mixins.scss

// Clear after floats
@mixin clearfix {
  zoom: 1;

  &:before,
  &:after {
    content: "\0020";
    display: block;
    height: 0;
    overflow: hidden;
  }

  &:after {
    clear: both;
  }
}

// Apply clearfix to this classes by default
.clearfix,
.group {
  @include clearfix;
}


// Responsive mixins
@mixin responsive($res) {
  @media screen and (min-width: $res) {
    @content;
  }
}

@mixin mobilefirst($res) {
  @media screen and (min-width: $res) {
    @content;
  }
}


// Slightly lighten a color
@function tint($color, $percentage) {
  @return mix(white, $color, $percentage);
}


// Slightly darken a color
@function shade($color, $percentage) {
  @return mix(black, $color, $percentage);
}


// Responsive ratio
@mixin responsive-ratio($x,$y, $pseudo: false) {
  $padding: unquote( ( $y / $x ) * 100 + '%' );
  @if $pseudo {
      &:before {
          @include pseudo($pos: relative);
          width: 100%;
          padding-top: $padding;
      }
  } @else {
      padding-top: $padding;
  }
}


// CSS triangles
@mixin css-triangle($color, $direction, $size: 6px, $position: absolute, $round: false){
  @include pseudo($pos: $position);
  width: 0;
  height: 0;
  @if $round {
      border-radius: 3px;
  }
  @if $direction == down {
      border-left: $size solid transparent;
      border-right: $size solid transparent;
      border-top: $size solid $color;
      margin-top: 0 - round( $size / 2.5 );
  } @else if $direction == up {
      border-left: $size solid transparent;
      border-right: $size solid transparent;
      border-bottom: $size solid $color;
      margin-bottom: 0 - round( $size / 2.5 );
  } @else if $direction == right {
      border-top: $size solid transparent;
      border-bottom: $size solid transparent;
      border-left: $size solid $color;
      margin-right: -$size;
  } @else if  $direction == left {
      border-top: $size solid transparent;
      border-bottom: $size solid transparent;
      border-right: $size solid $color;
      margin-left: -$size;
  }
}


//Placeholders
@mixin input-placeholder {
  &.placeholder { @content; }
  &:-moz-placeholder { @content; }
  &::-moz-placeholder { @content; }
  &:-ms-input-placeholder { @content; }
  &::-webkit-input-placeholder { @content; }
}


// Gradient
@mixin background-gradient($start-color, $end-color, $orientation) {
  background: $start-color;

  @if $orientation == 'vertical' {
    background: -webkit-linear-gradient(top, $start-color, $end-color);
    background: linear-gradient(to bottom, $start-color, $end-color);
  } @else if $orientation == 'horizontal' {
    background: -webkit-linear-gradient(left, $start-color, $end-color);
    background: linear-gradient(to right, $start-color, $end-color);
  } @else {
    background: -webkit-radial-gradient(center, ellipse cover, $start-color, $end-color);
    background: radial-gradient(ellipse at center, $start-color, $end-color);
  }
}
//Usage:
//$start-color, $end-color, $orientation - vertical/horizontal/radial
.foo {
  @include background-gradient(red, black, 'vertical');
}


//Animation mixin setup
@mixin keyframes($animation-name) {
  @-webkit-keyframes #{$animation-name} {
      @content;
  }
  @-moz-keyframes #{$animation-name} {
      @content;
  }
  @-ms-keyframes #{$animation-name} {
      @content;
  }
  @-o-keyframes #{$animation-name} {
      @content;
  }
  @keyframes #{$animation-name} {
      @content;
  }
}
@mixin animation($str) {
-webkit-animation: #{$str};
-moz-animation: #{$str};
-ms-animation: #{$str};
-o-animation: #{$str};
animation: #{$str};
}
//Usage
// Define animation name, and properties
@include keyframes(fade-out) {
0% { opacity: 1; }
90% { opacity: 0; }
}
// Add animation to element
.element {
width: 100px;
height: 100px;
background: black;
@include animation('fade-out 5s 3');
}


// Retina Images
@mixin image-2x($image, $width, $height) {
  @media (min--moz-device-pixel-ratio: 1.3),
         (-o-min-device-pixel-ratio: 2.6/2),
         (-webkit-min-device-pixel-ratio: 1.3),
         (min-device-pixel-ratio: 1.3),
         (min-resolution: 1.3dppx) {
    background-image: url($image);
    background-size: $width $height;
  }
}
//Usage
div.logo {
  background: url("logo.png") no-repeat;
  @include image-2x("logo2x.png", 100px, 25px);
}


// Cross Browser Opacity
@mixin opacity($opacity) {
  opacity: $opacity;
  $opacity-ie: $opacity * 100;
  filter: alpha(opacity=$opacity-ie); //IE8
}


// Box Shadow
@mixin boxshadow($horiz, $vert, $blur, $color) {
    box-shadow: $horiz $vert $blur $color;
}


// Inner Shadow
@mixin innershadow($horiz, $vert, $blur, $color) {
    box-shadow: inset $horiz $vert $blur $color;
}


// Drop Shadow
@mixin drop-shadow($color: fade-out(#000, 0.6), $size: 3px, $vertical-offset: 0px, $horizontal-offset: 0px) {
  box-shadow: $horizontal-offset $vertical-offset $size $color;
  -webkit-box-shadow: $horizontal-offset $vertical-offset $size $color;
  -moz-box-shadow: $horizontal-offset $vertical-offset $size $color;
}
@mixin drop-shadow-inset($color: fade-out(#000, 0.6), $size: 3px, $vertical-offset: 0px, $horizontal-offset: 0px) {
  box-shadow: inset $horizontal-offset $vertical-offset $size $color;
  -webkit-box-shadow: inset $horizontal-offset $vertical-offset $size $color;
  -moz-box-shadow: inset $horizontal-offset $vertical-offset $size $color;
}
@mixin drop-shadow-no() {
  box-shadow: none;
  -webkit-box-shadow: none;
  -moz-box-shadow: none;
}

/// Allows you to pass it arguments to easily output a
/// light or dark color of your choosing based on the
/// lightness of another color.
///
/// @param {Color} $background-color
/// @param {Color} $light-color [config-get('contrasting-color-light')]
/// @param {Color} $dark-color [config-get('contrasting-color-dark')]
///
/// @return {Color}
@function contrasting-color($background-color, $light-color: config-get("contrasting-color-light"), $dark-color: config-get("contrasting-color-dark")) {
  @if is-light($background-color) {
    @return $dark-color;
  } @else {
    @return $light-color;
  }
}