Unable to style checkboxes HTML/CSS

I'm unable to do any styling whatsoever on some HTML checkboxes. Any css fails to change the appearance of the checkboxes:

HTML:

<input type="checkbox" id="checkbox-1-1" class="regular-checkbox" />
    <nput type="checkbox" id="checkbox-1-2" class="regular-checkbox" />
    <input type="checkbox" id="checkbox-1-3" class="regular-checkbox" />
    <input type="checkbox" id="checkbox-1-4" class="regular-checkbox" />

CSS:

.regular-checkbox {
  position: absolute;
  top: 0;
  left: 0;
  height: 25px;
  width: 25px;
  background-color: #eee;
}

Checkbox is unchanged. Can anyone tell me what I'm doing wrong here? I thought this was possible in CSS.