FontAwesome is awesome if you need some quick icons somewhere. It’s easy to integrate and very flexible in usage. FontAwesome comes shipped with some CSS animations pre-defined (fa-spin, fa-pulse), but you can very easily extend it to have other helper classes, like this:

The following CSS Code was used for this:

.fa-beat {
  animation:fa-beat 5s ease infinite;
}
@keyframes fa-beat {
  0% {
    transform:scale(1);
  }
  5% {
    transform:scale(1.25);
  }
  20% {
    transform:scale(1);
  }
  30% {
    transform:scale(1);
  }
  35% {
    transform:scale(1.25);
  }
  50% {
    transform:scale(1);
  }
  55% {
    transform:scale(1.25);
  }
  70% {
    transform:scale(1);
  }
}

Attention: For cross-browser CSS animations you still need some vendor prefixes for older browsers. Check caniuse.com for detailed information.

Funktionsweise

Neben den entsprechenden Akkordion-Buttons befindet sich eine versteckte Checkbox.
Mithilfe des General sibling selectors (Allgemeiner Geschwister-Selektor) kann der Akkordion-Inhalt entsprechend dem Status der Checkbox verändert werden.

Also zum Beispiel:

.accordion-content {
  display:none;
}
input:checked ~ .accordion-content {
  display:block;
}