<div class="container">
  <span class="custom-tooltip">
    ТУЛТИП
  </span>
  <button>НАВЕДИ НА МЕНЯ</button>
</div>

.container {
  margin: 5rem;
  position: relative;
}
.custom-tooltip {
  display: none;
  position: absolute;
  top: -20px;
  left: 0%;
}

.custom-tooltip:has(+ *:hover) {
  display: block;
  background: red;
}