.addevent-button {
  display: block;
  cursor: pointer;
}

.addevent-button ~ ul {
  position: absolute;
  visibility: hidden;
  opacity: 0;
  height: 0;
  width: 100%;
  margin: 0;
  padding: 0;
  list-style: none;
  z-index: 100;
  -webkit-transition: all 0.5s ease;
  -moz-transition: all 0.5s ease;
  -ms-transition: all 0.5s ease;
  -o-transition: all 0.5s ease;
  transition: all 0.5s ease;
}

.addevent-button.open ~ ul {
  height: auto;
  visibility: visible;
  opacity: 1;
  background-color: white;
}

.addevent-button.open ~ ul li {
  border-bottom: solid 1px rgba(0, 0, 0, 0.1);
}

.addevent-button.open ~ ul li:last-child,
.addevent-button.open ~ ul li:last-of-type {
  border-bottom: none;
}