<div class="cp_ipcheck12">
  <label><input type="checkbox" name="cpipr12">ネコ</label>
  <label><input type="checkbox" name="cpipr12">イヌ</label>
  <label><input type="checkbox" name="cpipr12">ウサギ</label>
</div>

.cp_ipcheck12 {
  margin: 6em 2em;
}
.cp_ipcheck12 label {
  display: flex;
  align-items: center;
  cursor: pointer;
}
/*通常時のチェックボックスの設定*/
.cp_ipcheck12 input[type="checkbox"] {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 22px;
  height: 22px;
  border: 2px solid #666666;
  cursor: pointer;
  transition: .5s ease;
  /*デフォルト値を無効に*/
  appearance: none;
  outline: none;
}
.cp_ipcheck12 input[type="checkbox"]:after {
  position: absolute;
  content: '';
  transform-origin: center center;
  transition: .5s ease;
  opacity: 0;
}
/*checked時の設定*/
.cp_ipcheck12 input[type="checkbox"]:checked {
  border-radius: 100%;
  background-color: #da3c41;
  border: 2px solid #da3c41;
}
.cp_ipcheck12 input[type="checkbox"]:checked:after {
  content: '✔︎';
  color: #ffffff;
  opacity: 1;
  transform: scale(1, 1);
  transition: opacity .5s ease;
}