FAB squircle gradiente

.btn-169 {
  width: 56px;
  height: 56px;
  display: inline-grid;
  place-items: center;
  color: #fff;
  background: linear-gradient(135deg,#f472b6,#a855f7 60%,#6366f1);
  border: 0;
  border-radius: 18px;
  cursor: pointer;
  box-shadow: 0 8px 22px -6px #a855f7aa;
  transition: transform .2s,box-shadow .2s,border-radius .2s
}
.btn-169:hover {
  transform: translateY(-2px) rotate(-4deg);
  border-radius: 22px;
  box-shadow: 0 12px 28px -6px #a855f7cc
}
.btn-169:focus-visible {
  outline: 3px solid #a855f7;
  outline-offset: 3px
}
.btn-169:active {
  transform: scale(.95);
  border-radius: 16px;
  box-shadow: 0 4px 10px -4px #a855f7aa
}

<button class="btn-169" aria-label="Compose"><svg width="22" height="22" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.2" stroke-linecap="round" stroke-linejoin="round"><path d="M4 20l4-1 10-10-3-3L5 16z"/></svg></button>