Styling default checkbox using SASS.

HTML

<div class="custom-checkbox">
    <label>
        <input type="checkbox" name="">                                                   
        <span class="checkbox-icon"></span>
        <span class="checkbox-text">Select</span>
   </label>
</div>                 

Color Variables

$primary_color    : #000;
$fonts_1          : FontAwesome;

Mixins

@mixin transition($transition...){
  transition: $transition;
  -webkit-transition: $transition;
  -moz-transition: $transition;
  -ms-transition: $transition;
  -o-transition: $transition;
}

@mixin transform($transform...){
  transform: $transform;
  -webkit-transform: $transform;
  -moz-transform: $transform;
  -ms-transform: $transform;
  -o-transform: $transform;
}

SASS Structure

.custom-checkbox{
	position: relative;
	display: inline-block;
	min-height: 19px;
	padding: 0px 0px 0px 27px;

	label{
		margin: 0;
		padding: 0;
		display: block;
	}
	.checkbox-icon{
		width: 19px;
		height: 19px;
		display: block;
		background: lighten($primary_color, 95%);
		border: lighten($primary_color, 80%) 1px solid;
		position: absolute;
		top: 0px;
		left: 0px;
		text-align: center;

		&::before{
			content: "\f00c";
			font-family: $fonts_1;
			font-size: 13px;
			color: lighten($primary_color, 40%);
			display: block;

			opacity: 0;
			filter: alpha(opacity=0);

			@include transition(all ease 0.2s);
                        @include transform(translate(4px, 0px));
		}
	}
	input{
		display: none;

		&:checked + span.checkbox-icon{

			&::before{
				opacity:1;
				filter: alpha(opacity=100);

                               @include transform(translate(0px, 0px));
			}
		}
	}

	.checkbox-text{
		font-size: 14px;
		padding-top: 1px;
	}
}