checkbox.css

/* Styles for hiding the native checkbox */
input[type='checkbox'].check-custom {
  top: 0;
  left: 0;
  width: 0;
  height: 0;
  opacity: 0;
  filter: alpha(opacity=0);
  position: absolute;
  visibility: hidden;
}

/* Styles for the basic appearance of the custom checkbox */
input[type='checkbox'].check-custom ~ .check-toggle {
  width: 1rem;
  height: 1rem;
  position: relative;
  display: inline-block;
  vertical-align: middle;
  border: 2px solid #969696;
  border-radius: 50%;
  cursor: pointer;
}

/* Styles for the hover state appearance of the custom checkbox */
input[type='checkbox'].check-custom:hover ~ .check-toggle {
  border-color: #4a4a4a;
}

/* Styles for the checked state appearance of the custom checkbox */
input[type='checkbox'].check-custom:checked ~ .check-toggle {
  border-color: #1785ff;
  background: #1785ff url(data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSIxNiIgaGVpZ2h0PSIxNiIgdmlld0JveD0iMCAwIDI0IDI0IiBmaWxsPSJub25lIiBzdHJva2U9IiNmZmZmZmYiIHN0cm9rZS13aWR0aD0iMyIgc3Ryb2tlLWxpbmVjYXA9InJvdW5kIiBzdHJva2UtbGluZWpvaW49InJvdW5kIj48cG9seWxpbmUgcG9pbnRzPSIyMCA2IDkgMTcgNCAxMiI+PC9wb2x5bGluZT48L3N2Zz4=) center no-repeat;
  background-size: 75%;
}