app/assets/stylesheets/custom_checkboxes.css
/**
 * @info Custom Imageless CSS Skinning for Checkboxes and Radiobuttons
 * @author Martin Ivanov
 * @web http://wemakesites.net
 * @blog http://acidmartin.wordpress.com/
 * @twitter https://twitter.com/wemakesitesnet
 */

:root .css3-radios label,
:root .css3-radios input[type="radio"] + span,
:root .css3-radios input[type="radio"] + span::before,
:root .css3-checkboxes label,
:root .css3-checkboxes input[type="checkbox"] + span,
:root .css3-checkboxes input[type="checkbox"] + span::before
{
    display: inline-block;
    vertical-align: middle;
}

:root label.css3-checkboxes
{
  margin-bottom: 0px;
}

:root .css3-radios,
:root .css3-checkboxes
{
    position: relative;
}

:root .css3-radios label *,
:root .css3-checkboxes label *
{
    cursor: pointer;
}

:root .css3-radios input[type="radio"],
:root .css3-checkboxes input[type="checkbox"]
{
    opacity: 0;
    position: absolute;
}

:root .css3-radios input[type="radio"] + span,
:root .css3-checkboxes input[type="checkbox"] + span
{
/*    color: #000;*/
}

:root .css3-radios input[type="radio"]:hover + span,
:root .css3-radios input[type="radio"]:focus + span,
:root .css3-checkboxes input[type="checkbox"]:hover + span,
:root .css3-checkboxes input[type="checkbox"]:focus + span
{
/*    color: #000000;*/
}

:root .css3-radios input[type="radio"]:focus + span,
:root .css3-checkboxes input[type="checkbox"]:focus + span
{
    border:1px dotted black;
    margin: -1px;
}


:root .css3-radios input[type="radio"]:hover:disabled + span,
:root .css3-radios input[type="radio"]:focus:disabled + span,
:root .css3-checkboxes input[type="checkbox"]:hover:disabled + span
:root .css3-checkboxes input[type="checkbox"]:focus:disabled + span
{
/*    color: #000;*/
}

:root .css3-radios label:hover span::before,
:root .css3-radios label:focus span::before,
:root .css3-checkboxes label:hover span::before
:root .css3-checkboxes label:focus span::before
{
    -moz-box-shadow: 0 0 2px #ccc;
    -webkit-box-shadow: 0 0 2px #ccc;
    box-shadow: 0 0 2px #ccc;
}

:root .css3-radios label:hover span,
:root .css3-radios label:focus span,
:root .css3-checkboxes label:hover span
:root .css3-checkboxes label:focus span
{
/*    color: #000;*/
}

:root .css3-radios input[type="radio"] + span::before,
:root .css3-checkboxes input[type="checkbox"] + span::before
{
    content: "";
    width: 18px;
    height: 18px;
    margin: 0 4px 2px 0;
    border: solid 2px #2c3e50;
    line-height: 14px;
    text-align: center;

    -moz-border-radius: 100%;
    -webkit-border-radius: 100%;
    border-radius: 100%;

    background: #fff;
}

:root .css3-radios input[type="radio"]:checked + span::before,
:root .css3-checkboxes input[type="checkbox"]:checked + span::before
{
    color: #000;
}

:root .css3-radios input[type="radio"]:disabled + span:before,
:root .css3-checkboxes input[type="checkbox"]:disabled + span:before
{
    -moz-opacity: .4;
    -webkit-opacity: .4;
    opacity: .4;
}

:root .css3-radios input[type="radio"]:disabled + span,
:root .css3-checkboxes input[type="checkbox"]:disabled + span
{
    cursor: default;
}

:root .css3-checkboxes input[type="checkbox"] + span::before
{
    -moz-border-radius: 4px;
    -webkit-border-radius: 4px;
    border-radius: 4px;
}

:root .css3-radios input[type="radio"]:checked + span::before
{
    content: "\2022";
    font-size: 24px;
}

:root .css3-checkboxes input[type="checkbox"]:checked + span::before
{
    content: "\2714";
    font-size: 24px;
    /*color: #000000;*/
}

/*
 * Modified Bootstrap code
 */

.radios,
.checkboxes {
  display: block;
  min-height: 21px;
  margin-bottom: 10px;
  vertical-align: middle;
}

.radios label,
.checkboxes label {
  display: inline;
  margin-bottom: 0;
  font-weight: normal;
  cursor: pointer;
  font-weight: bold;
}

.radios input[type="radio"],
.radio-inline input[type="radio"],
.checkboxes input[type="checkbox"],
.checkbox-inline input[type="checkbox"] {
  float: left;
}

.radios + .radio,
.checkboxes + .checkbox {
  margin-top: -5px;
}

.radio-inline,
.checkbox-inline {
  display: inline-block;
  padding-left: 20px;
  margin-bottom: 0;
  font-weight: normal;
  vertical-align: middle;
  cursor: pointer;
}

.radio-inline + .radio-inline,
.checkbox-inline + .checkbox-inline {
  margin-top: 0;
  margin-left: 10px;
}

input[type="radio"][disabled],
input[type="checkbox"][disabled],
.radio[disabled],
.radio-inline[disabled],
.checkboxes[disabled],
.checkbox-inline[disabled],
fieldset[disabled] input[type="radio"],
fieldset[disabled] input[type="checkbox"],
fieldset[disabled] .radio,
fieldset[disabled] .radio-inline,
fieldset[disabled] .checkboxes,
fieldset[disabled] .checkbox-inline {
  cursor: not-allowed;
}