github.com/mithrandie/csvq@v1.18.1/docs/_sass/components/forms/_checkboxes.scss

/* Checkboxes
   ========================================================================== */

/* CUSTOM CSS CHECKBOXES */
form p {
  margin-bottom: 10px;
  text-align: left;
}

form p:last-child {
  margin-bottom: 0;
}

/* Remove default checkbox */
[type="checkbox"]:not(:checked),
[type="checkbox"]:checked {
  position: absolute;
  left: -9999px;
  opacity: 0;
}

// Checkbox Styles
[type="checkbox"] {
  // Text Label Style
  + label {
    position: relative;
    padding-left: 35px;
    cursor: pointer;
    display: inline-block;
    height: 25px;
    line-height: 25px;
    font-size: 1rem;

    -webkit-user-select: none; /* webkit (safari, chrome) browsers */
    -moz-user-select: none; /* mozilla browsers */
    -khtml-user-select: none; /* webkit (konqueror) browsers */
    -ms-user-select: none; /* IE10+ */
  }

  /* checkbox aspect */
  + label:before,
  &:not(.filled-in) + label:after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 18px;
    height: 18px;
    z-index: 0;
    border: 2px solid $radio-empty-color;
    border-radius: 1px;
    margin-top: 2px;
    transition: .2s;
  }

  &:not(.filled-in) + label:after {
    border: 0;
    transform: scale(0);
  }

  &:not(:checked):disabled + label:before {
    border: none;
    background-color: $input-disabled-color;
  }

  // Focused styles
  &.tabbed:focus + label:after {
    transform: scale(1);
    border: 0;
    border-radius: 50%;
    box-shadow: 0 0 0 10px rgba(0,0,0,.1);
    background-color: rgba(0,0,0,.1);
  }
}

[type="checkbox"]:checked {
  + label:before {
    top: -4px;
    left: -5px;
    width: 12px;
    height: 22px;
    border-top: 2px solid transparent;
    border-left: 2px solid transparent;
    border-right: $radio-border;
    border-bottom: $radio-border;
    transform: rotate(40deg);
    backface-visibility: hidden;
    transform-origin: 100% 100%;
  }

  &:disabled + label:before {
    border-right: 2px solid $input-disabled-color;
    border-bottom: 2px solid $input-disabled-color;
  }
}

/* Indeterminate checkbox */
[type="checkbox"]:indeterminate {
  +label:before {
    top: -11px;
    left: -12px;
    width: 10px;
    height: 22px;
    border-top: none;
    border-left: none;
    border-right: $radio-border;
    border-bottom: none;
    transform: rotate(90deg);
    backface-visibility: hidden;
    transform-origin: 100% 100%;
  }

  // Disabled indeterminate
  &:disabled + label:before {
    border-right: 2px solid $input-disabled-color;
    background-color: transparent;
  }
}

// Filled in Style
[type="checkbox"].filled-in {
  // General
  + label:after {
    border-radius: 2px;
  }

  + label:before,
  + label:after {
    content: '';
    left: 0;
    position: absolute;
    /* .1s delay is for check animation */
    transition: border .25s, background-color .25s, width .20s .1s, height .20s .1s, top .20s .1s, left .20s .1s;
    z-index: 1;
  }

  // Unchecked style
  &:not(:checked) + label:before {
    width: 0;
    height: 0;
    border: 3px solid transparent;
    left: 6px;
    top: 10px;

    -webkit-transform: rotateZ(37deg);
    transform: rotateZ(37deg);
    -webkit-transform-origin: 20% 40%;
    transform-origin: 100% 100%;
  }

  &:not(:checked) + label:after {
    height: 20px;
    width: 20px;
    background-color: transparent;
    border: 2px solid $radio-empty-color;
    top: 0px;
    z-index: 0;
  }

  // Checked style
  &:checked {
    + label:before {
      top: 0;
      left: 1px;
      width: 8px;
      height: 13px;
      border-top: 2px solid transparent;
      border-left: 2px solid transparent;
      border-right: 2px solid $input-background;
      border-bottom: 2px solid $input-background;
      -webkit-transform: rotateZ(37deg);
      transform: rotateZ(37deg);

      -webkit-transform-origin: 100% 100%;
      transform-origin: 100% 100%;
    }

    + label:after {
      top: 0;
      width: 20px;
      height: 20px;
      border: 2px solid $secondary-color;
      background-color: $secondary-color;
      z-index: 0;
    }
  }

  // Focused styles
  &.tabbed:focus + label:after {
    border-radius: 2px;
    border-color: $radio-empty-color;
    background-color: rgba(0,0,0,.1);
  }

  &.tabbed:checked:focus + label:after {
    border-radius: 2px;
    background-color: $secondary-color;
    border-color: $secondary-color;
  }

  // Disabled style
  &:disabled:not(:checked) + label:before {
    background-color: transparent;
    border: 2px solid transparent;
  }

  &:disabled:not(:checked) + label:after {
    border-color: transparent;
    background-color: $input-disabled-solid-color;
  }

  &:disabled:checked + label:before {
    background-color: transparent;
  }

  &:disabled:checked + label:after {
    background-color: $input-disabled-solid-color;
    border-color: $input-disabled-solid-color;
  }
}