.custom-tooltip.bs-tooltip-auto[data-popper-placement^=top] .tooltip-arrow::before,
.custom-tooltip.bs-tooltip-top .tooltip-arrow::before {
  border-top-color: #1da1f2; /* match background */
}

.custom-tooltip .tooltip-inner {
  background-color: #1da1f2; /* your blue background */
  color: #fff;
  padding: 12px 16px;
  border-radius: 8px;
  max-width: 300px;
}