<button>click me</button>
<button class="unset">click me</button>
<button class="appearance--none">click me</button>
<button class="manually--reset">click me</button>

.unset {
  all: unset;
  outline: revert; /* keep this for keyboard focus */
}

.appearance--none {
  appearance: none;
}

.manually--reset {
  background: none;
  border: none;
  padding: 0;
}