Freedom-Loader/public/styles/button/checkbox.css

/* From Uiverse.io by bociKond */ 
/* Hide the default checkbox */
.checkbox-mp3 input {
  position: absolute;
  opacity: 0;
  cursor: pointer;
  height: 0;
  width: 0;
}

.checkbox-mp3 {
  display: block;
  position: relative;
  cursor: pointer;
  font-size: 1.5rem;
  user-select: none;
}

/* Create a custom checkbox */
.checkmark {
  --clr: #0B6E4F;
  position: relative;
  top: 0;
  left: 0;
  height: 1.3em;
  width: 1.3em;
  background-color: #ccc;
  border-radius: 50%;
  transition: 300ms;
}

/* When the checkbox is checked, add a blue background */
.checkbox-mp3 input:checked ~ .checkmark {
  background-color: var(--clr);
  border-radius: .5rem;
  animation: pulse 500ms ease-in-out;
}

/* Create the checkmark/indicator (hidden when not checked) */
.checkmark:after {
  content: "";
  position: absolute;
  display: none;
}

/* Show the checkmark when checked */
.checkbox-mp3 input:checked ~ .checkmark:after {
  display: block;
}

/* Style the checkmark/indicator */
.container .checkmark:after {
  left: 0.45em;
  top: 0.25em;
  width: 0.25em;
  height: 0.5em;
  border: solid #E0E0E2;
  border-width: 0 0.15em 0.15em 0;
  transform: rotate(45deg);
}

@keyframes pulse {
  0% {
    box-shadow: 0 0 0 #0B6E4F90;
    rotate: 20deg;
  }

  50% {
    rotate: -20deg;
  }

  75% {
    box-shadow: 0 0 0 10px #0B6E4F60;
  }

  100% {
    box-shadow: 0 0 0 13px #0B6E4F30;
    rotate: 0;
  }
}