<ul class="unstyled centered">
  <li>
    <input class="styled-checkbox" id="styled-checkbox-1" type="checkbox" value="value1">
    <label for="styled-checkbox-1">Checkbox</label>
  </li>
  <li>
    <input class="styled-checkbox" id="styled-checkbox-2" type="checkbox" value="value2" checked>
    <label for="styled-checkbox-2">CSS Only</label>
  </li>
  <li>
    <input class="styled-checkbox" id="styled-checkbox-3" type="checkbox" value="value3" disabled>
    <label for="styled-checkbox-3">A disabled checkbox</label>
  </li>
  <li>
    <input class="styled-checkbox" id="styled-checkbox-4" type="checkbox" value="value4">
    <label for="styled-checkbox-4">Fourth option</label>
  </li>
</ul>

.styled-checkbox {
  position: absolute; // take it out of document flow
  opacity: 0; // hide it

  & + label {
    position: relative;
    cursor: pointer;
    padding: 0;
  }

  // Box.
  & + label:before {
    content: '';
    margin-right: 10px;
    display: inline-block;
    vertical-align: text-top;
    width: 20px;
    height: 20px;
    background: white;
  }

  // Box hover
  &:hover + label:before {
    background: #f35429;
  }
  
  // Box focus
  &:focus + label:before {
    box-shadow: 0 0 0 3px rgba(0, 0, 0, 0.12);
  }

  // Box checked
  &:checked + label:before {
    background: #f35429;
  }
  
  // Disabled state label.
  &:disabled + label {
    color: #b8b8b8;
    cursor: auto;
  }

  // Disabled box.
  &:disabled + label:before {
    box-shadow: none;
    background: #ddd;
  }

  // Checkmark. Could be replaced with an image
  &:checked + label:after {
    content: '';
    position: absolute;
    left: 5px;
    top: 9px;
    background: white;
    width: 2px;
    height: 2px;
    box-shadow: 
      2px 0 0 white,
      4px 0 0 white,
      4px -2px 0 white,
      4px -4px 0 white,
      4px -6px 0 white,
      4px -8px 0 white;
    transform: rotate(45deg);
  }
}

// Demo-only styles
// --------------

html {
  background: lightgray;
}

body {
  font-family: 'Source Sans Pro', sans-serif;
}

.unstyled {
  margin: 0;
  padding: 0;
  list-style-type: none;
}

li {
  margin: 20px 0;
}

.centered {
  width: 300px;
  margin: auto;
}

.title {
  text-align: center;
  color: rgb(69, 113, 236);
}

// Pure CSS custom checkboxes.

// Reference: https://css-tricks.com/snippets/css/custom-checkboxes-and-radio-buttons/
// and: http://www.456bereastreet.com/archive/201211/accessible_custom_checkboxes_and_radio_buttons/