.mentioner {
  position: relative;
}

.mentioner__composer {
  border-radius: 3px;
  padding: 10px;

  background-color: #F5F5F5;
  outline: none;
}

.mentioner__dropdown {
  max-width: 250px;
  position: absolute;

  &--hidden {
    display: none;
  }
}

.mentioner {
  position: relative;
}

.mentioner__composer {
  border-radius: 3px;
  padding: 10px;

  background-color: #F5F5F5;
  outline: none;
}

.mentioner__dropdown {
  max-width: 250px;
  position: absolute;
  z-index: 99999;

  &--hidden {
    display: none;
  }
}

Add an absurdly high z-index for the dropdown
Add an absurdly high z-index for the dropdown
